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Biomedical subjects

M F Rohde

Publications and source records attributed to M F Rohde.

At least 37 records · Page 2Linked to original sources
PubMed1995

CD14: physical properties and identification of an exposed site that is protected by lipopolysaccharide.

Soluble CD14 (sCD14) is a 55-kDa serum protein that binds lipopolysaccharide (LPS) and mediates LPS-dependent responses in a variety of cells. Using recombinant sCD14 expressed in Chinese hamster ovary (CHO) cells, we examined the structural characteristics of sCD14 and sCD14.LPS complexes. The circular dichroism and fluorescence spectra of the sCD14 indicate that it contains substantial beta-sheet (40%) and a well-defined tertiary structure with the tryptophan residues located in environments with different degrees of hydrophobicity and solvent exposure. The spectra of the sCD14.LPS complex are identical within experimental error to the uncomplexed sCD14. Changes in surface accessibility upon LPS binding were examined using limited proteolysis with endoproteinase Asp-N. This analysis revealed that aspartic acid residues at amino acids 57, 59, and 65 are susceptible to cleavage by Asp-N, while the same residues are protected from proteolytic cleavage in the sCD14.LPS complex. These results suggest that a region including amino acids 57 to 64 is involved in LPS binding by sCD14.

Amino Acid Sequence↗
PubMed1994

Structural requirements for addition of O-linked carbohydrate to recombinant erythropoietin.

To define the structural requirements for addition of O-linked glycosylation in vivo, recombinant erythropoietin (rEPO) variants were constructed. Thirty-three independent Ser or Thr substitutions were constructed and examined to see which were subject to O-linked carbohydrate addition. Variants with Thr mutations at positions 123 and 125, but not elsewhere, contained additional carbohydrate, which suggests that several positions around the existing O-linked glycosylation site (Ser126), but not elsewhere, contain the necessary information for O-linked carbohydrate addition. Two forms of the Thr125 variant were identified. One form was glycosylated only at residue 125, and a second form was glycosylated at both Thr125 and Ser126, the normal O-glycosylation site. We have also found that glycosylation is less efficient when rEPO is improperly folded and that prolines at -1 and +1 relative to the O-glycosylation site enhance glycosylation.

Amino Acid Sequence↗
PubMed1994

Characterization of disulfide linkages in platelet-derived growth factor AA.

Intermolecular and intramolecular disulfide linkages of recombinant human platelet-derived growth factor A chain dimer were determined by chemical methods including selective reduction-alkylation, peptide isolation, or detection of diphenylthiohydantoin derivative of cystine from Edman reactions. Cys-37 and Cys-46 were selectively reduced with reducing agents under native conditions and revealed to be involved in intermolecular bridges. Other disulfide linkages including Cys-10-Cys-54, Cys-43-Cys-91, and Cys-47-Cys-93 form intramolecular bridges. The disulfide structure is homologous to that of platelet-derived growth factor B chain dimer.

Alkylation↗
PubMed1994

A set of endoplasmic reticulum proteins possessing properties of molecular chaperones includes Ca(2+)-binding proteins and members of the thioredoxin superfamily.

The major proteins in the lumen of the endoplasmic reticulum (ER) are thought to function in Ca2+ sequestration or as "molecular chaperones" in the folding and assembly of membrane or secreted proteins. Based on the ability of many chaperones to bind selectively to unfolded proteins and to dissociate from them upon ATP hydrolysis, we developed an affinity chromatography method to isolate proteins with these characteristics from pancreatic or liver ER. Seven ER proteins bound selectively to denatured protein columns and were specifically eluted by ATP (10(-6) M) but not by a nonhydrolyzable ATP analog. These proteins were identified with antibodies and microsequencing as the ER chaperone BiP (grp78), grp94, calreticulin, a novel 46-kDa protein that binds azido-ATP, as well as three members of the thioredoxin superfamily: protein-disulfide isomerase, ERp72, and a previously reported 50-kDa protein (p50). This set of seven proteins bound to and was eluted with ATP from a variety of denatured proteins, including histone, gelatin, alpha fetoprotein, thyroglobulin, lysozyme, casein, and IgG. The release of grp94, protein-disulfide isomerase, ERp72, calreticulin, and p50 was stimulated by Ca2+ in the presence of ATP. These proteins thus appear to function as Ca(2+)-dependent chaperones, which may account for the Ca2+ and ATP requirement for protein folding in the ER.

Adenosine Triphosphate↗
PubMed1994

Direct assignment of disulfide bonds by Edman degradation of selected peptide fragments.

Disulfide linkages in peptides or proteins were analyzed by automated gas-phase Edman sequencing performed in minimized reducing agents. If cystine linkage was regulated at the same position in two peptides during peptide preparation, the diphenylthiohydantoin derivative of cystine was significantly recovered by Edman reaction. In contrast, when the crosslinked half cystines were present at different positions in the peptides, the derivative could be poorly detected. Upon direct sequence analysis of intact bovine insulin, the PTH derivatives of cystine from both Cys-A7 and Cys-B7 were significantly released after Edman cycle 7 and gave approximately 20% recovery of common PTH amino acids. However, Cys-A11 linked to Cys-A6 was poorly detectable after Edman cycle 11. For general use of this method, proteins need to be subjected to several sets of proteolytic or chemical cleavages in the hope that at least one of the fragments will have cystine linkage at the same position. This method was applied to several fragments of platelet-derived growth factor B chain and brain-derived neurotrophic factor.

Acetylation↗
PubMed1993

Covalent dimerization of recombinant human interferon-gamma.

An apparently nonreducible covalent dimer has been consistently observed as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). These studies endeavor to understand the nature of this covalent dimerization. Amino acid sequence analysis of a recombinant human interferon-gamma stored for 2 years showed a major sequence starting with the intact N-terminal methionine and a minor sequence corresponding to the C-terminal seven amino acids of the intact protein. Moreover, when the same material was analyzed by gel filtration in the presence of 8 M urea, a minor peak corresponding to the dimer was observed prior to the monomer peak. Reducing and nonreducing SDS-PAGE also showed a minor band corresponding to a dimer. These results suggest that the reactions of C-terminal processing and dimerization have occurred during storage. Reverse-phase chromatography of stored, unfractionated material showed three peaks. Mass spectral analysis of the first, second, and third peaks gave molecular weights of 16,900, 16,100, and 33,000. Since no major cleavage was observed in the N-terminal region of the protein, the observed masses suggest that the first peak corresponds to residues 1 to 144 (a full-length molecule), the second peak to residues 1 to 137 (des 7 interferon-gamma), and the third peak to a dimer. Calculation of theoretical molecular weight from the amino acid sequence suggests that this dimer corresponds to some combination of the intact protein and des 7 protein. Tryptic peptide maps in conjunction with sequence and mass analyses identified a new tryptic peptide in the map of the dimer corresponding to residue 133 to 137 followed by residues 1 to 7. The conclusion is recombinant methionyl human interferon-gamma undergoes a specific cleavage at the C-terminal side of residue 137 phenylalanine, and a conventional peptide bond was formed between residues 137 and 1 methionine.

Amino Acid Sequence↗
PubMed1993

Peptide mapping and evaluation of glycopeptide microheterogeneity derived from endoproteinase digestion of erythropoietin by affinity high-performance capillary electrophoresis.

High-performance capillary electrophoresis (HPCE) has been employed to characterize the peptide map of recombinant human erythropoietin (rHuEPO) expressed from Chinese hamster ovary (CHO) cells. The methodology employs an ion pairing agent, 100 mM heptanesulfonic acid in 40 mM sodium phosphate buffer, pH 2.5, to increase peptide resolution, to decrease analyte wall interactions, and to evaluate glycopeptide microheterogeneity. The total tryptic map is segregated into two regions, nonglycosylated and glycosylated peptides. Reproducibility of the peptide map is excellent; the map results in baseline separation of 16 tryptic peptides and one doublet peak composed of two peptides (resolution 0.22). The map furthermore allows for the evaluation of the microheterogeneity associated with the three rHuEPO glycopeptides. At least 12 glycopeptide forms were separated in the initial peptide map. Peptides were identified by Edman sequencing, and the glycopeptides were further subjected to Dionex anion-exchange chromatography. To simplify the level of complexity associated with the glycopeptides, much of the characterization employed asialoglycopeptides and employed several endoproteolytic diagnosis. The relative percent distribution for each purified asialoglycopeptide was calculated to define the level of complexity and to tentatively assign a known structure to the HPCE peak. The level of structural complexity of the asialoglycopeptides appears to increase from the simplest O-linked form to the more complex N83, N38, and N24 glycosylation positions, respectively. HPCE evaluation of glycopeptide microheterogeneity appears to be simpler, faster, and just as sensitive as other more frequently employed methods for glycopeptide characterizations.

Animals↗
PubMed1993

Disulfide bonds in recombinant human platelet-derived growth factor BB dimer: characterization of intermolecular and intramolecular disulfide linkages.

Interchain cystines of PDGF-BB dimer were characterized by Edman reaction and by SDS-PAGE analysis on the protein which was chemically cleaved at Trp-40. It was found that Cys-43 has a key role in dimer formation, asymmetrically cross-linked to a cysteine residue of another identical subunit. The remaining cystines participate in the intramolecular disulfide linkages. Pepsin digestion of PDGF-BB dimer generated several small peptides and one ubiquitous Cys-containing peptide. Sequence analyses of several Cys-containing peptides indicated the existence of three intramolecular disulfide linkages including Cys-16--Cys-60, Cys-49--Cys-97, and Cys-53--Cys-99. Two interchain disulfide bonds of Cys-43--Cys-52 between two subunits were deduced from the partial reduction and alkylation of PDGF-BB. This study provides chemically determined disulfide linkages of PDGF-BB.

Acetylation↗
PubMed1993

Recombinant human erythropoietin (rHuEPO): cross-linking with disuccinimidyl esters and identification of the interfacing domains in EPO.

Several amino groups of recombinant human erythropoietin are selectively cross-linked by specific cross-linkers including disuccinimidyl suberate or dithiobis(succinimidyl propionate). Intramolecular cross-linkings are obtained without significant change of the protein conformation using appropriate concentrations (0.2 mM) of the cross-linkers, which possess an 11-12-A length of a spacer between two reacting groups. Intramolecularly cross-linked peptides obtained suggest that several amino groups in erythropoietin (EPO) are positioned at a distance of near 12 A in the solution state. These interfacing amino groups include Lys 20-Lys 154, Lys 45-Lys 140, Lys 52-Lys 154, Lys 52-Lys 140, and Ala 1-Lys 116. A comparison of the cross-linking results between nonglycosylated EPO and glycosylated EPO suggests that both proteins retain high similarity regarding protein conformation. These results fit a structural model similar to that of human growth hormone, in which four alpha-helical bundles and a long stretch of beta-sheet structure are involved in the active protein.

Amino Acid Sequence↗
PubMed1993

Sites of iodination in recombinant human brain-derived neurotrophic factor and its effect on neurotrophic activity.

Recombinant human brain-derived neurotrophic factor (BDNF) is now under extensive investigation because of its potential clinical applications. Radioactively labeled proteins are usually required to study receptor binding and pharmacokinetic properties of proteins. This study was undertaken to see if iodination affects the biological and conformational properties of a recombinant BDNF. BDNF was iodinated using a stoichiometric amount of nonradioactive cold NaI to minimize multiple iodinations. Of the four tyrosines present in BDNF--Tyr-52, Tyr-54, Tyr-63, and Tyr-86--only Tyr-63 and Tyr-86 were iodinated under the experimental conditions used. Iodination of Tyr-63 resulted in modification without alteration of the biological activity, whereas iodination of Tyr-86 resulted in a molecule with highly compromised biological activity. Similar inactivation was observed if both Tyr-63 and Tyr-86 were iodinated. These modified proteins exhibited conformation and dimerization apparently identical to those of the native protein, as demonstrated by analytical ultracentrifugation, gel filtration, light scattering, and circular dichroism. From these results, we concluded that Tyr-52 and Tyr-54 are not accessible to the reagent and are probably buried in the hydrophobic core, whereas Tyr-63 and Tyr-86 are exposed on the surface of the molecule; of the two exposed residues, only Tyr-86 contributes to the biological activity.

Amino Acid Sequence↗
PubMed1993

Isolation and characterization of three recombinant human granulocyte colony stimulating factor His-->Gln isoforms produced in Escherichia coli.

This report demonstrates that three variant isoforms of recombinant methionyl human granulocyte colony stimulating factor are present in small quantities in the crude preparation solubilized from Escherichia coli inclusion bodies. These isoforms were separated from the main form of the factor during purification and further isolated by a series of cationic exchange chromatographic separations. They exhibit full in vitro biological activity and have slightly lower pI's. Structural characterization of the intact proteins and their isolated peptides by sequence determination and mass spectrometric analysis revealed that they are methionyl granulocyte colony stimulating factors having a His-->Gln replacement at sequence position 53, 157, or 171, respectively. The specific His-->Gln change suggests the occurrence of mistranslation during protein synthesis. These variant forms are chromatographically separable during purification and are not detectable in the final purified form of the factor.

Amino Acid Sequence↗
PubMed1993

Mutation of Arg55/56 to Leu55/Ala56 in insulin-like growth factor-I results in two forms different in disulfide structure and native conformation but similar under reverse-phase conditions.

Folding of recombinant human insulin-like growth factor-I (IGF-I) results in two distinct species as resolved by reversed-phase high-performance liquid chromatography (RP-HPLC). The earlier eluting peak (PI) has a nonnative disulfide structure, while the later eluting peak (PII) assumes the native disulfide structure. This folding problem causes a lower yield and requires expensive RP-HPLC separation. In contrast, IGF-II folds mainly into a single form with all three disulfide bonds correctly formed. Sequence comparison of the two molecules revealed that IGF-I has arginine at residues 55 and 56, while IGF-II has alanine and leucine, respectively, at these positions. Two analogs of IGF-I, IGF-I (Ala55/Leu56) and IGF-I (Leu56), behave similarly to IGF-II upon refolding and RP-HPLC; that is, a single peak eluted from the RP-HPLC column. However, when the peaks isolated by RP-HPLC were subjected to hydrophobic interaction chromatography, circular dichroism, and peptide mapping, they were found to be a mixture of PI and PII. It was then concluded that factors other than just these two residues contribute to correct folding of IGF-II and that the PI and PII of the above two IGF-I mutants assume different conformation at neutral pH but similar conformation under the RP-HPLC condition.

Alanine↗
PubMed1993

The effect of the platelet-derived glycosaminoglycan serglycin on in vitro proplatelet-like process formation.

The formation of proplatelet-like processes on megakaryocytes cultured in vitro has been shown to be inhibited by prothrombin, found residually in human serum, which is converted in culture to thrombin. This study reports that another factor found in human serum will counter this inhibition and permit proplatelet-like process formation to occur in vitro even in the presence of inhibitory concentrations of thrombin. The factor was purified from human platelet lysates and identified by amino acid sequence analysis as the proteoglycan serglycin. A similar, if not identical, factor was found at elevated levels in the plasma of thrombocytopenic rabbits. Serglycin probably functions as a proplatelet potentiator by virtue of a tendency to complex with thrombin. Thrombin in complex with serglycin retains its enzymatic properties, but is apparently sterically hindered from interacting with the megakaryocyte cell surface. In preliminary studies, the in vivo administration of serglycin in mice resulted in an increased number of circulating platelets when given in combination with interleukin-6 (IL-6).

Amino Acid Sequence↗
PubMed1993

Recombinant human brain-derived neurotrophic factor (rHuBDNF). Disulfide structure and characterization of BDNF expressed in CHO cells.

Three disulfide linkages of recombinant human brain-derived neurotrophic factor (BDNF) were determined by peptide sequence analysis and characterized by mass spectrometry. The three disulfide bonds for BDNF expressed in Chinese hamster ovary cells include Cys-13-Cys-80, Cys-58-Cys-109 and Cys-68-Cys-111, and the disulfide structure was homologous to that of nerve growth factor.

Amino Acid Sequence↗
PubMed1992

Cloning and characterization of a gene encoding extracellular metalloprotease from Streptomyces lividans.

The prt gene, encoding a protease (Prt) from Streptomyces lividans TK24, was cloned and sequenced. An S. lividans host with plasmid-borne prt secreted 200 micrograms/ml of a 22-kDa Prt into the culture medium. Prt is classified as a metalloprotease since its activity is significantly inhibited by 1,10-phenanthroline or EDTA. The region upstream from prt codes for an incomplete open reading frame (ORF) oriented opposite to prt. This ORF has a strong similarity to a gene family (lysR) whose members regulate the transcription of structural genes required for either biosynthesis or degradation.

Amino Acid Sequence↗
PubMed1992

Induced resistance of trypsin to sodium dodecylsulfate upon complex formation with trypsin inhibitor.

The stabilities of trypsin and soybean trypsin inhibitor in sodium dodecylsulfate (SDS) were examined by SDS-polyacrylamide gel electrophoresis (PAGE). Both samples contained several bands, all of which migrated to positions corresponding to the appropriate molecular weight or less, even when the samples were unheated, suggesting that both the trypsin and trypsin inhibitor are susceptible to SDS-induced denaturation. When they were mixed together prior to addition of SDS-PAGE sample buffer (1% SDS), a new smearing band appeared which corresponded to a molecular weight of around 46,000, suggesting that these proteins form a stable complex in SDS. This was confirmed by electroblotting and sequence analysis, which indicated that this band contains both the trypsin and inhibitor sequences. At a fixed concentration of the inhibitor, increasing concentrations of the trypsin resulted in an increase in the intensity of the complex band. When the mixture was heated for 10 min in 1% SDS, the complex band disappeared in a temperature-dependent manner. The melting temperature determined under the experimental conditions used was about 35 degrees C. Similar results were obtained with Bowman-Birk trypsin inhibitor, except that the complex with the above inhibitor had a higher melting temperature, around 41 degrees C, suggesting that the Bowman-Birk inhibitor/trypsin complex is more stable than the soybean inhibitor/trypsin complex.

Electrophoresis, Polyacrylamide Gel↗
PubMed1992

Circular dichroism of reduced and oxidized recombinant human epidermal growth factor.

To further elucidate the role of the disulfide bonds in determining the protein folding of recombinant human epidermal growth factor (r-HuEGF) we studied the structure of reduced and oxidized r-HuEGF using circular dichroism (CD). The far UV CD spectrum of reduced r-HuEGF in 10 mM sodium phosphate pH 3.0 is very different from that of the oxidized molecule. The spectrum of the reduced molecule consists of a plateau from 225 to 200 nm, consistent with the presence of alpha-helix, beta-sheet, and unordered structure. The addition of the alpha-helix inducer trifluoroethanol to the reduced molecule resulted in an enhancement of alpha-helix, at the apparent expense of beta-sheet, while the oxidized molecule was unaffected by the presence of this reagent. Secondary structure predictions based on the amino acid sequence of EGF correlate most closely with the structure of the reduced molecule. From these results, it appears that the r-HuEGF has a more regular secondary structure in the absence of the disulfide bonds than in their presence. This suggests that the folding of EGF occurs by destroying the regular secondary structure that was present in the reduced state, and that the structure of the native molecule is dictated largely by disulfide bonding.

Circular Dichroism↗