Biomedical subjects

Gregg B Fields

Publications and source records attributed to Gregg B Fields.

At least 19 recordsLinked to original sources

PubMed2006

The roles of substrate thermal stability and P2 and P1' subsite identity on matrix metalloproteinase triple-helical peptidase activity and collagen specificity.

The hydrolysis of collagen (collagenolysis) is one of the committed steps in extracellular matrix turnover. Within the matrix metalloproteinase (MMP) family distinct preferences for collagen types are seen. The substrate determinants that may guide these specificities are unknown. In this study, we have utilized 12 triple-helical substrates in combination with 10 MMPs to better define the contributions of substrate sequence and thermal stability toward triple helicase activity and collagen specificity. In general, MMP-13 was found to be distinct from MMP-8 and MT1-MMP(Delta279-523), in that enhanced substrate thermal stability has only a modest effect on activity, regardless of sequence. This result correlates to the unique collagen specificity of MMP-13 compared with MMP-8 and MT1-MMP, in that MMP-13 hydrolyzes type II collagen efficiently, whereas MMP-8 and MT1-MMP are similar in their preference for type I collagen. In turn, MMP-1 was the least efficient of the collagenolytic MMPs at processing increasingly thermal stable triple helices and thus favors type III collagen, which has a relatively flexible cleavage site. Gelatinases (MMP-2 and MMP-9(Delta444-707)) appear incapable of processing more stable helices and are thus mechanistically distinct from collagenolytic MMPs. The collagen specificity of MMPs appears to be based on a combination of substrate sequence and thermal stability. Analysis of the hydrolysis of triple-helical peptides by an MMP mutant indicated that Tyr(210) functions in triple helix binding and hydrolysis, but not in processing triple helices of increasing thermal stabilities. Further exploration of MMP active sites and exosites, in combination with substrate conformation, may prove valuable for additional dissection of collagenolysis and yield information useful in the design of more selective MMP inhibitors.

Amino Acid Sequence↗

PubMed2005

A novel conotoxin framework with a helix-loop-helix (Cs alpha/alpha) fold.

Venomous predatory animals, such as snakes, spiders, scorpions, sea anemones, and cone snails, produce a variety of highly stable cystine-constrained peptide scaffolds as part of their neurochemical strategy for capturing prey. Here we report a new family of four-cystine, three-loop conotoxins (designated framework 14). Three peptides of this family (flf14a-c) were isolated from the venom of Conus floridanus floridensis, and one (vil14a) was isolated from the venom of Conus villepinii, two worm-hunting Western Atlantic cone snail species. The primary structure for these peptides was determined using Edman degradation sequencing, and their cystine pairing was assessed by limited hydrolysis with a combination of CNBr and chymotrypsin under nonreducing, nonalkylating conditions in combination with MALDI-TOF MS analysis of the resulting peptidic fragments. CD spectra and nanoNMR spectroscopy of these conotoxins directly isolated from the cone snails revealed a highly helical secondary structure for the four conotoxins. Sequence-specific nanoNMR analysis at room temperature revealed a well-defined helix-loop-helix tertiary structure that resembles that of the Cs alpha/alpha scorpion toxins kappa-hefutoxin, kappa-KTx1.3, and Om-toxins, which adopt a stable three-dimensional fold where the two alpha-helices are linked by the two disulfide bridges. One of these conotoxins (vil14a) has a Lys/Tyr dyad, separated by approximately 6A, which is a conserved structural feature in K(+) channel blockers. The presence of this framework in scorpions and in cone snails indicates a common molecular imprint in the venom of apparently unrelated predatory animals and suggests a common ancestral genetic origin.

Amino Acid Sequence↗

PubMed2005

Polypeptide chains containing D-gamma-hydroxyvaline.

Life has an unexplained and distinct l-homochirality. Proteins typically incorporate only l-amino acids into their sequences. In the present study, d-Val and d-gamma-hydroxyvaline (d-Hyv; V) have been found within ribosomally expressed polypeptide chains. Four conopeptides were initially isolated, gld-V/gld-V'from the venom of Conus gladiator and mus-V/mus-V' from the venom of Conus mus. Their complete sequences (gld-V/gld-V' = Ala-Hyp-Ala-Asn-Ser-d-Hyv-Trp-Ser and mus-V/mus-V' = Ser-Hyp-Ala-Asn-Ser-d-Hyv-Trp-Ser) were determined by a combination of nano/pico-NMR and MS/MS methods. The amino acid triad that contains the gamma-hydroxylated residue, Ser-d-Hyv-Trp, is a novel structural motif that is stabilized by specific interactions between the d-amino acid and its neighboring l-counterparts. These interactions inhibit lactonization, a peptide backbone scission process that would normally be initiated by gamma-hydroxylated residues. Conopeptides possessing the Ser-d-Hyv-Trp motif have been termed gamma-hydroxyconophans. We have also isolated analogous conopeptides (gld-V and mus-V) containing d-Val instead of d-Hyv; these are termed conophans. gamma-Hydroxyconophans and conophans are particularly atypical because (i) they are not constrained as most conopeptides, (ii) they are extremely short in length, (iii) they have a high content of hydroxylated residues, and (iv) their sequences have no close match with other peptides in sequence databases. Their modifications appear to be part of a novel hyperhydroxylation mechanism found within the venom of cone snails that enhances neuronal targeting. The finding of d-Val and d-Hyv within this family of peptides suggests the existence of a corresponding d-stereospecific enzyme capable of d-Val oxidation.

Amino Acid Sequence↗

PubMed2004

Matrix metalloproteinase triple-helical peptidase activities are differentially regulated by substrate stability.

Matrix metalloproteinases (MMPs) are involved in physiological remodeling as well as pathological destruction of tissues. The turnover of the collagen triple-helical structure has been ascribed to several members of the MMP family, but the determinants for collagenolytic specificity have not been identified. The present study has compared the triple-helical peptidase activities of MMP-1 and MMP-14 (membrane-type 1 MMP; MT1-MMP). The ability of each enzyme to efficiently hydrolyze the triple helix was quantified using chemically synthesized fluorogenic triple-helical substrates that, via addition of N-terminal alkyl chains, differ in their thermal stabilities. One series of substrates was modeled after a collagenolytic MMP consensus cleavage site from types I-III collagen, while the other series had a single substitution in the P(1)' subsite of the consensus sequence. The substitution of Cys(4-methoxybenzyl) for Leu in the P(1)' subsite was greatly favored by MMP-14 but disfavored by MMP-1. An increase in substrate triple-helical thermal stability led to the decreased ability of the enzyme to cleave such substrates, but with a much more pronounced effect for MMP-1. Increased thermal stability was detrimental to enzyme turnover of substrate (k(cat)), but not binding (K(M)). Activation energies were considerably lower for MMP-14 hydrolysis of triple-helical substrates compared with MMP-1. Overall, MMP-1 was found to be less efficient at processing triple-helical structures than MMP-14. These results demonstrate that collagenolytic MMPs have subtle differences in their abilities to hydrolyze triple helices and may explain the relative collagen specificity of MMP-1.

Amino Acid Sequence↗

PubMed2004

Differential modulation of human melanoma cell metalloproteinase expression by alpha2beta1 integrin and CD44 triple-helical ligands derived from type IV collagen.

Tumor cell binding to components of the basement membrane is well known to trigger intracellular signaling pathways. Signaling ultimately results in the modulation of gene expression, facilitating metastasis. Type IV collagen is the major structural component of the basement membrane and is known to be a polyvalent ligand, possessing sequences bound by the alpha1beta1, alpha2beta1, and alpha3beta1 integrins, as well as cell surface proteoglycan receptors, such as CD44/chondroitin sulfate proteoglycan (CSPG). The role of alpha2beta1 integrin and CD44/CSPG receptor binding on human melanoma cell activation has been evaluated herein using triple-helical peptide ligands incorporating the alpha1(IV)382-393 and alpha1(IV)1263-1277 sequences, respectively. Gene expression and protein production of matrix metalloproteinases-1 (MMP-1), -2, -3, -13, and -14 were modulated with the alpha2beta1-specific sequence, whereas the CD44-specific sequence yielded significant stimulation of MMP-8 and lower levels of modulation of MMP-1, -2, -13, and -14. Analysis of enzyme activity confirmed different melanoma cell proteolytic potentials based on engagement of either the alpha2beta1 integrin or CD44/CSPG. These results are indicative of specific activation events that tumor cells undergo upon binding to select regions of basement membrane collagen. Based on the present study, triple-helical peptide ligands provide a general approach for monitoring the regulation of proteolysis in cellular systems.

Amino Acid Sequence↗

PubMed2004

Collagenase unwinds triple-helical collagen prior to peptide bond hydrolysis.

Breakdown of triple-helical interstitial collagens is essential in embryonic development, organ morphogenesis and tissue remodelling and repair. Aberrant collagenolysis may result in diseases such as arthritis, cancer, atherosclerosis, aneurysm and fibrosis. In vertebrates, it is initiated by collagenases belonging to the matrix metalloproteinase (MMP) family. The three-dimensional structure of a prototypic collagenase, MMP-1, indicates that the substrate-binding site of the enzyme is too narrow to accommodate triple-helical collagen. Here we report that collagenases bind and locally unwind the triple-helical structure before hydrolyzing the peptide bonds. Mutation of the catalytically essential residue Glu200 of MMP-1 to Ala resulted in a catalytically inactive enzyme, but in its presence noncollagenolytic proteinases digested collagen into typical 3/4 and 1/4 fragments, indicating that the MMP-1(E200A) mutant unwinds the triple-helical collagen. The study also shows that MMP-1 preferentially interacts with the alpha2(I) chain of type I collagen and cleaves the three alpha chains in succession. Our results throw light on the basic mechanisms that control a wide range of biological and pathological processes associated with tissue remodelling.

Amino Acid Sequence↗

PubMed2004

Catalytic- and ecto-domains of membrane type 1-matrix metalloproteinase have similar inhibition profiles but distinct endopeptidase activities.

Membrane type 1-matrix metalloproteinase (MT1-MMP/MMP-14) is a major collagenolytic enzyme that plays a vital role in development and morphogenesis. To elucidate further the structure-function relationship between the human MT1-MMP active site and the influence of the haemopexin domain on catalysis, substrate specificity and inhibition kinetics of the cdMT1-MMP (catalytic domain of MT1-MMP) and the ecto domain DeltaTM-MT1-MMP (transmembrane-domain-deleted MT1-MMP) were compared. For substrate 1 [Mca-Pro-Leu-Gly-Leu-Dpa-Ala-Arg-NH(2), where Mca stands for (7-methoxycoumarin-4-yl)acetyl- and Dpa for N -3-(2,4-dinitrophenyl)-L-2,3-diaminopropionyl], the activation energy E (a) was determined to be 11.2 and 12.2 kcal/mol (1 cal=4.184 J) for cdMT1-MMP and DeltaTM-MT1-MMP respectively, which is consistent with k (cat)/ K (M) values of 7.37 and 1.46x10(4) M(-1).s(-1). The k (cat)/ K (M) values for a series of similar single-stranded peptide substrates were determined and found to correlate with a slope of 0.17 for the two enzyme forms. A triple-helical peptide substrate was predicted to have a k (cat)/ K (M) of 0.87x10(4) M(-1).s(-1) for DeltaTM-MT1-MMP based on the value for cdMT1-MMP of 5.12x10(4) M(-1).s(-1); however, the actual value was determined to be 2.5-fold higher, i.e. 2.18x10(4) M(-1).s(-1). These results suggest that cdMT1-MMP is catalytically more efficient towards small peptide substrates than DeltaTM-MT1-MMP and the haemopexin domain of MT1-MMP facilitates the hydrolysis of triple-helical substrates. Diastereomeric inhibitor pairs were utilized to probe further binding similarities at the active site. Ratios of K (i) values for the inhibitor pairs were found to correlate between the enzyme forms with a slope of 1.03, suggesting that the haemopexin domain does not significantly modify the enzyme active-site structure.

Binding Sites↗

PubMed2004

Contributions of the MMP-2 collagen binding domain to gelatin cleavage. Substrate binding via the collagen binding domain is required for hydrolysis of gelatin but not short peptides.

Two matrix metalloproteinases, MMP-2 and MMP-9, contain each three fibronectin type II-like modules, which form their collagen binding domains (CBDs). The contributions of CBD substrate interactions to the catalytic activities of these gelatinases have attracted special interest. Recombinant (r) CBDs retain collagen binding properties and deletions of CBDs in these MMPs reduce activities on collagen and elastin. We have characterized further the requirement of the CBD for MMP-2 cleavage of gelatin. The analyses used intact rMMP-2 and rCBD to eliminate any confounding effects that might result from structural perturbations in rMMP-2 induced by deletion of the approximately 20 kDa internal CBD. In protein-protein binding assays, 2% DMSO disrupted gelatin interactions of both rCBD and rMMP-2. At this concentration, DMSO also reduced the gelatinolytic activity by approximately 70%, pointing to a central role of CBD-substrate interactions during MMP-2 cleavage of gelatin. Subsequently, soluble rCBD was determined to competitively inhibit gelatin binding of unmodified rMMP-2 to gelatin by 73% and to reduce the MMP-2 degradation of gelatin by 70-80%. The residual gelatin cleavage that was not inhibited even by molar excess rCBD could be accounted for by degradation of short substrate molecules. Indeed, rCBD inhibited rMMP-2 cleavage of an 11 amino acid collagen-like peptide substrate (NFF-1) by less than 10%. These observations were confirmed with enzyme extracts from experimental tumors in mice. In the presence of rCBD, approximately 65% of the MMP-derived gelatinolytic activity was eliminated. Together, these results demonstrate that the CBD is absolutely required for MMP-2 cleavage of full-length collagen alpha-chains, but not for short protein fragments such as those generated by hydrolysis of gelatin.

Animals↗

PubMed2004

Development of a solid-phase assay for analysis of matrix metalloproteinase activity.

Proteases play fundamentally important roles in normal physiology and disease pathology. Methods for detection of active proteolysis may greatly aid in the diagnosis of disease progression, and suggest modes of therapeutic intervention. Most assays for proteolytic potential are limited by a lack of specificity and/or quantification. We have developed a solid-phase activity assay for members of the matrix metalloproteinase (MMP) family that is specific and can be used to quantify active enzyme concentration. The assay has two principal components: a capture antibody that immobilizes the MMP without perturbing the enzyme active site, and a fluorescence resonance energy transfer substrate for monitoring proteolysis at low enzyme concentrations. The assay was standardized for MMP-1, MMP-3, MMP-13, and MMP-14. The efficiency of the assay was found to be critically dependent upon the quality of the antibodies, the use of substrates exhibiting high specific activities for the enzymes, and enzyme samples that are fresh. The assay was applied to studies of constitutive and induced MMP activity in human melanoma cells. Analysis of several melanoma cell lines, and comparison with prior studies, correlated higher constitutive MMP-13 activity with higher levels of the cell surface receptor CD44. Ligands to two different melanoma cell surface receptors (the alpha2beta1 integrin or CD44) were found to induce different proteolytic profiles, suggesting that the extracellular matrix can modulate melanoma invasion. Overall, the solid-phase MMP activity assay was found to be valuable for analysis of protease activity in cellular environments. The solid-phase assay is suitably flexible to allow studies of virtually any proteolytic enzyme for which appropriate substrates and antibodies are available.

Amino Acid Sequence↗

PubMed2003

Regulation of collagenase activities of human cathepsins by glycosaminoglycans.

Cathepsin K, a lysosomal papain-like cysteine protease, forms collagenolytically highly active complexes with chondroitin sulfate and represents the most potent mammalian collagenase. Here we demonstrate that complex formation with glycosaminoglycans (GAGs) is unique for cathepsin K among human papain-like cysteine proteases and that different GAGs compete for the binding to cathepsin K. GAGs predominantly expressed in bone and cartilage, such as chondroitin and keratan sulfates, enhance the collagenolytic activity of cathepsin K, whereas dermatan, heparan sulfate, and heparin selectively inhibit this activity. Moreover, GAGs potently inhibit the collagenase activity of other cysteine proteases such as cathepsins L and S at 37 degrees C. Along this line MMP1-generated collagen fragments in the presence of GAGs are stable against further degradation at 28 degrees C by all cathepsins but cathepsin K, whereas thermal destabilization at 37 degrees C renders the fragments accessible to all cathepsins. These results suggest a novel mechanism for the regulation of matrix protein degradation by GAGs. It further implies that cathepsin K represents the only lysosomal collagenolytic activity under physiologically relevant conditions.

Animals↗

PubMed2003

Induction of endothelial cell activation by a triple helical alpha2beta integrin ligand, derived from type I collagen alpha1(I)496-507.

Endothelial cell activation involves the elevated expression of cell adhesion molecules, chemoattractants, chemokines, and cytokines. These expression profiles may be regulated by integrin-mediated cell signaling pathways. In the current study, an alpha2beta1 integrin triple helical peptide ligand derived from type I collagen residues alpha1(I)496-507 was examined for induction of human aortic endothelial cell (HAEC) activation. In addition, a "miniextracellular matrix" composed of a mixture of the alpha1(I)496-507 ligand and a second, alpha-helical ligand incorporating the endothelial cell proliferating region of SPARC (secreted protein acidic and rich in cysteine) was studied for induction of HAEC activation. Following HAEC adhesion to alpha1(I)496-507, mRNA expression of E-selectin-1, vascular and intercellular cell adhesion molecules-1, and monocytic chemoattractant protein-1 was stimulated, whereas that of endothelin-1 was inhibited. Enzyme-linked immunosorbent assay analysis demonstrated that E-selectin-1 and monocytic chemoattractant protein-1 expression was also stimulated, whereas endothelin-1 protein expression diminished. Engagement of the alpha2beta1 integrin initiated a HAEC response similar to that of tumor necrosis factor-alpha-induced HAECs but was not sufficient to induce an inflammatory response. Addition of the SPARC119-122 region had only a slight effect on HAEC activation. Other cell-extracellular matrix interactions appear to be required to elicit an inflammatory response. The alpha2beta1 integrin specific triple helical peptide ligand described herein represents a more general in vitro model system by which gene expression and protein production profiles induced by binding to a single cellular receptor type can be quantified.

Aorta↗

PubMed2003

Analysis of matrix metalloproteinase triple-helical peptidase activity with substrates incorporating fluorogenic L- or D-amino acids.

The consequences of improper regulation of collagen turnover include diseases such as tumor cell metastasis and arthritis. Several fluorogenic triple-helical peptide (fTHP) substrates have been constructed presently to examine collagenolytic behavior. These substrates incorporate L- or D-2-amino-3-(7-methoxy-4-coumaryl)propionic acid (Amp) or L- or D-2-amino-3-(6,7-dimethoxy-4-coumaryl)propionic acid (Adp) as the fluorophore and N-2,4-dinitrophenyl (Dnp) as the quencher. The desired sequences were C6-(Gly-Pro-Hyp)5-Gly-Pro-[Amp/Adp]-Gly-Pro-Gln-Gly approximately Leu-Arg-Gly-Gln-Lys(Dnp)-Gly-Val-Arg-(Gly-Pro-Hyp)5-NH2. All four fTHPs formed stable triple-helices. Matrix metalloproteinase-2 (MMP-2) rates of hydrolysis for all fTHPs were considerably more rapid than corresponding MMP-1 rates. Evaluation of individual kinetic parameters indicated that MMP-2 bound to the fTHPs more efficiently than MMP-1. Comparison to a triple-helical substrate incorporating the same sequence but with a different fluorophore [Lys((7-methoxycoumarin-4-yl)acetyl); Lys(Mca)] demonstrated that the shorter side chain of Amp or Adp was better tolerated by MMP-1 and MMP-2. Adp may well be the fluorophore of choice for fTHPs, as (a) fTHPs incorporating Adp were obtained in significantly higher yields than the Amp-containing fTHPs, (b) Adp has a larger Stokes shift than either Amp or Lys(Mca) and thus has less chance of self-quenching, (c) Adp has a relatively high quantum yield, (d) the Adp/Dnp pair is compatible with multiwell plate reader formats, and (e) MMPs better tolerate Adp than Lys(Mca).

Amino Acid Sequence↗

PubMed2003

Angiogenesis in collagen I requires alpha2beta1 ligation of a GFP*GER sequence and possibly p38 MAPK activation and focal adhesion disassembly.

Angiogenesis depends on proper collagen biosynthesis and cross-linking, and type I collagen is an ideal angiogenic scaffold, although its mechanism is unknown. We examined angiogenesis using an assay wherein confluent monolayers of human umbilical vein endothelial cells were overlain with collagen in a serum-free defined medium. Small spaces formed in the cell layer by 2 h, and cells formed net-like arrays by 6-8 h and capillary-like lumens by 24 h. Blocking of alpha2beta1, but not alpha1 or alpha(v)beta3 integrin function halted morphogenesis. We found that a triple-helical, homotrimeric peptide mimetic of a putative alpha2beta1 binding site: alpha1(I)496-507 GARGERGFP*GER (where single-letter amino acid nomenclature is used, P* = hydroxyproline) inhibited tube formation, whereas a peptide carrying another putative site: alpha1(I)127-138 GLP*GERGRP*GAP* or control peptides did not. A chemical inhibitor of p38 mitogen-activated protein kinase (p38 MAPK), SB202190, blocked tube formation, and p38 MAPK activity was increased in collagen-treated cultures, whereas targeting MAPK kinase (MEK), focal adhesion kinase (FAK), or phosphatidylinositol 3-kinase (PI3K) had little effect. Collagen-treated cells had fewer focal adhesions and 3- to 5-fold less activated FAK. Thus capillary morphogenesis requires endothelial alpha2beta1 integrin engagement of a single type I collagen integrin-binding site, possibly signaling via p38 MAPK and focal adhesion disassembly/FAK inactivation.

Binding Sites↗

PubMed2003

Selective hydrolysis of triple-helical substrates by matrix metalloproteinase-2 and -9.

The role of proteases in the tumor cell invasion process is multifaceted. Members of the matrix metalloproteinase (MMP) family have been implicated in primary and metastatic tumor growth, angiogenesis, and degradation of extracellular matrix (ECM) components. Differentiating between the up-regulation of MMP production and the presence of activated MMPs can be difficult but may well dictate which MMPs are critical to invasion. Because the hydrolysis of collagens is one of the committed steps in ECM turnover, we have investigated selective MMP action on collagenous substrates as a means to evaluate active MMPs. Two triple-helical peptide (THP) models of the MMP-9 cleavage site in type V collagen, alpha1(V)436-450 THP and alpha1(V)436-447 fTHP, were hydrolyzed by MMP-2 and MMP-9 at the Gly-Val bond, analogous to the bond cleaved by MMP-9 in the corresponding native collagen. Kinetic analyses showed k(cat)/K(m) values of 14,002 and 5,449 s(-1)m(-1) for MMP-2 and -9 hydrolysis of alpha1(V)436-447 fTHP, respectively. These values, along with individual k(cat) and K(m) values, are comparable with collagen hydrolysis by MMP-2 and -9. Neither THP was hydrolyzed by MMP-1, -3, -13, or -14. alpha1(V)436-447 fTHP and a general fluorogenic THP were used to screen for triple-helical peptidase activity in alpha(2)beta(1) integrin-stimulated melanoma cells. Binding of the alpha(2)beta(1) integrin resulted in the production of substantial triple-helical peptidase activity, the majority (>95%) of which was non-MMP-2/-9. THPs were found to provide highly selective substrates for members of the MMP family and can be used to evaluate active MMP production in cellular systems.

Circular Dichroism↗

PubMed2003

Melanoma cell CD44 interaction with the alpha 1(IV)1263-1277 region from basement membrane collagen is modulated by ligand glycosylation.

Invasion of the basement membrane is believed to be a critical step in the metastatic process. Melanoma cells have been shown previously to bind distinct triple-helical regions within basement membrane (type IV) collagen. Additionally, tumor cell binding sites within type IV collagen contain glycosylated hydroxylysine residues. In the present study, we have utilized triple-helical models of the type IV collagen alpha1(IV)1263-1277 sequence to (a) determine the melanoma cell receptor for this ligand and (b) analyze the results of single-site glycosylation on melanoma cell recognition. Receptor identification was achieved by a combination of methods, including (a) cell adhesion and spreading assays using triple-helical alpha1(IV)1263-1277 and an Asp(1266)Abu variant, (b) inhibition of cell adhesion and spreading assays, and (c) triple-helical alpha1(IV)1263-1277 affinity chromatography with whole cell lysates and glycosaminoglycans. Triple-helical alpha1(IV)1263-1277 was bound by melanoma cell CD44/chondroitin sulfate proteoglycan receptors and not by the collagen-binding integrins or melanoma-associated proteoglycan. Melanoma cell adhesion to and spreading on the triple-helical alpha1(IV)1263-1277 sequence was then compared for glycosylated (replacement of Lys(1265) with Hyl(O-beta-d-galactopyranosyl)) versus non-glycosylated ligand. Glycosylation was found to strongly modulate both activities, as adhesion and spreading were dramatically decreased due to the presence of galactose. CD44/chondroitin sulfate proteoglycan did not bind to glycosylated alpha1(IV)1263-1277. Overall, this study (a) is the first demonstration of the prophylactic effects of glycosylation on tumor cell interaction with the basement membrane, (b) provides a rare example of an apparent unfavorable interaction between carbohydrates, and (c) suggests that sugars may mask "cryptic sites" accessible to tumor cells with cell surface or secreted glycosidase activities.

Amino Acids↗

PubMed2002

Modulation of triple-helical stability and subsequent melanoma cellular responses by single-site substitution of fluoroproline derivatives.

Collagen is a multifunctional protein, serving as a structural scaffold and a modulator of cellular responses. Prior work has identified distinct regions from several collagen types that promote cell adhesion, spreading, migration, and signal transduction. One of these regions, alpha1(IV)1263-1277 from type IV collagen, mediates these responses via melanoma cell CD44-chondrotin sulfate proteoglycan receptors. In the study presented here, we have used a triple-helical model of alpha1(IV)1263-1277 to evaluate (a) conformational stability and (b) cellular responses based on single-site incorporation of trans-4-fluoro-L-proline (trans-Flp) or cis-4-fluoro-L-proline (cis-Flp) for trans-4-hydroxy-L-proline (trans-Hyp). The structural effects of cis-Flp and trans-Flp substitution were studied by circular dichroism and NMR spectroscopies. The peptide containing a single trans-Flp instead of trans-Hyp was slightly more thermally stable than the parent peptide (T(m) = 37 vs 34 degrees C), while the peptide containing cis-Flp was considerably less stable than the parent peptide (T(m) = 30 degrees C). Melanoma cell adhesion and spreading were examined under conditions where the trans-Hyp-, trans-Flp-, and cis-Flp-containing ligands were approximately 15, <10, and approximately 65% denatured, respectively. Adhesion to each of the three ligands was remarkably sensitive to the respective ligand conformation, with EC(50) values of approximately 2.5, approximately 0.35, and >5.0 microM for the trans-Hyp-, trans-Flp-, and cis-Flp-containing ligands, respectively. Melanoma cell spreading was quantitated over a ligand concentration range of 0.01-50 microM and, in a fashion similar to adhesion, was more extensive on the trans-Flp ligand than on the trans-Hyp ligand. Very low levels of spreading were observed with the cis-Flp-containing ligand at all concentrations tested. Melanoma cell adhesion to and spreading on the three ligands suggested the dramatic biological consequence of even subtle changes in relative triple-helical content. Such subtle changes may model those occurring in the basement membrane during the tumor cell invasion process, and thus provide mechanistic insight into this stage of metastasis.

Amino Acid Sequence↗

PubMed2002

Matrix metalloproteinases and collagen catabolism.

The matrix metalloproteinase (MMP)/matrixin family has been implicated in both normal tissue remodeling and a variety of diseases associated with abnormal turnover of extracellular matrix components. The mechanism by which MMPs catabolize collagen (collagenolysis) is still largely unknown. Substrate flexibility, MMP active sites, and MMP exosites all contribute to collagen degradation. It has recently been demonstrated that the ability to cleave a triple helix (triple-helical peptidase activity) can be distinguished from the ability to cleave collagen (collagenolytic activity). This suggests that the ability to cleave a triple helix is not the limiting factor for collagenolytic activity-the ability to properly orient and potentially destabilize collagen is. For the MMP family, the catalytic domain can unwind and cleave a triple-helical structure, while the C-terminal hemopexin-like domain appears to be responsible for properly orienting collagen and destabilizing it to some degree. It is also possible that exosites within the catalytic and/or C-terminal hemopexin-like domain may exclude some MMPs from cleaving collagen. Overall, it appears that many proteases of distinct mechanisms possess triple-helical peptidase activity, and that convergent evolution led to a few proteases possessing collagenolytic activity. Proper orientation and distortion of the triple helix may be the key factor for collagenolysis.

Carbohydrate Sequence↗

PubMedDate not supplied

Characterization of peptide-amphiphiles possessing cellular activation sequences.

Numerous approaches have been described for modifying biomaterials to incorporate extracellular matrix components. "Peptide-amphiphiles", whereby monoalkyl hydrocarbon chains are covalently linked to peptide sequences, have been shown previously to (a) form specific molecular architecture with enhanced stability and (b) promote cell adhesion, spreading, and signaling. The present study has examined the use of chimeric peptide-amphiphiles for inducing protein-like structures and peptide-amphiphile mixtures for enhancing surface bioactivity. The alpha-helical propensity of a 21 residue peptide, incorporating the SPARC(119-122) angiogenesis-inducing sequence and either unmodified or acylated with a C(6), C(10), C(14), C(16), C(18), C(18:1), or C(18:1-OH) monoalkyl hydrocarbon chain, has been examined. Peptide and peptide-amphiphile structures were characterized by circular dichroism and one- and two-dimensional NMR spectroscopic techniques. The 21 residue peptide alone does not form a distinct structure in solution, whereas N-terminal acylation by monoalkyl hydrocarbon chains results in the 21 residue peptide-amphiphile adopting a predominantly alpha-helical structure in solution. The thermal stability of the alpha-helix increases with increasing hydrocarbon chain length. The SPARC(119-122) peptide-amphiphiles were then screened for promotion of endothelial cell adhesion and spreading. The greatest activity was achieved by using a mixture of the alpha-helical SPARC(119-122) peptide-amphiphile, a triple-helical peptide-amphiphile incorporating the alpha2beta1 integrin binding site from type I collagen, and a pseudolipid. The pseudolipid is most likely required for a spatial distribution of the peptide-amphiphiles that allows for optimal cellular interactions. Overall, we have found that incorporation of bioactive sequences within peptide-amphiphiles results in the induction of an ordered structure of the bioactive sequence and that mixtures of peptide-amphiphiles can be used to promote endothelial cell behaviors comparable to extracellular matrix components.

Amino Acid Sequence↗