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J Greer

Publications and source records attributed to J Greer.

At least 37 records · Page 2Linked to original sources
PubMed1988

New inhibitors of human renin that contain novel Leu-Val replacements. Examination of the P1 site.

Stereoselective syntheses of several nonpeptide sulfidoethanol fragments that function as Leu10-Val11 (P1-P1') scissile bond replacements in human angiotensinogen are presented. These fragments are prepared from a variety of amino acids with formal P1 side chains varying in size and lipophilicity by converting them to their corresponding N-protected aminoalkyl epoxide 5 followed by ring opening with isopropyl mercaptan. The coupling of these fragments to either Boc-Phe-Ala-OH or Boc-Phe-His-OH produces inhibitors of human renin, 6 and 7, respectively, which are compared to a series of dipeptide-aldehyde inhibitors, 4, by molecular modeling and biochemical methods. Qualitatively, histidine-containing (P2) inhibitors 7 possess greater inhibitory potency than their corresponding alanine (P2) analogues 6, which are more potent than the corresponding aldehydic inhibitors from series 4. Within a given series, inhibitors with the cyclohexylmethyl P1 side chain are more potent than the benzyl analogues, which in turn are more potent than cyclohexyl or isobutyl derivatives. Inhibitors with parger P1 side chains (e.g. adamantylmethyl and benzhydryl) are much less active. The inhibitory potency of these compounds against human renin is discussed in terms of specific interactions with the enzyme.

Amino Acid Sequence↗
PubMed1988

Secondary structure of complement component C3a anaphylatoxin in solution as determined by NMR spectroscopy: differences between crystal and solution conformations.

Two-dimensional 1H NMR investigations were used to locate elements of regular secondary structure in the human complement protein C3a (the des-Arg77 derivative) in solution. The results were compared to a refined crystal structure based on the 3.2-A resolution structure of des-Arg77-C3a [Huber, R., Scholze, H., Paques, E. P. & Deisenhofer, J. (1980) Hoppe-Seyler's Z. Physiol. Chem. 361, 1389-1399]. In excellent agreement with the x-ray data, helices occur in the regions of residues 17-28 and 36-43 in solution. In contrast to the x-ray data, where a third long helix was found from residue 47 to residue 73, the solution data show a shorter helix in the region from residue 47 to residue 66, followed by a transition range at positions 67-70, leading into a six-residue carboxyl-terminal peptide in dynamic random coil conformation. At the amino terminus, a well-defined helix is observed in solution for the residues 8-15 region, which, like the carboxyl terminus, gradually changes to dynamic random coil toward the end of the polypeptide chain. This is at variance with the x-ray data as well, in which residues 13-15 are nonhelical and no electron density could be assigned to the first 12 residues due to disorder.

Anaphylatoxins↗
PubMed1987

Renin inhibitors. Dipeptide analogues of angiotensinogen incorporating transition-state, nonpeptidic replacements at the scissile bond.

A series of dipeptide analogues of angiotensinogen have been prepared and evaluated for their ability to inhibit the aspartic proteinase renin. The compounds were derived from the renin substrate by replacing the scissile amide bond with a transition-state mimic and by incorporating bioisosteric replacements for the Val-10 amide bond. Analogue 21a exhibited an IC50 of 7.6 nM against purified human renin, showed high specificity for this enzyme, and produced a hypotensive response in anesthetized, salt-depleted cynomolgus monkeys.

Angiotensinogen↗
PubMed1986

Peptide analogues of angiotensinogen. Effect of peptide chain length on renin inhibition.

Renin inhibition was evaluated for a series of peptide analogues of angiotensinogen with different chain lengths. Systematic deletion of amino acid residues from the hexapeptide BocPheHisLeuR-ValIleHisOCH3 showed that the presence of residues at the N-terminal Phe and His positions was essential for efficient enzyme-inhibitor binding whereas the C-terminal Ile and His residues were much less important. Synthesis of a tetrapeptide analogue shortened at the C-terminus and containing modified side chains produced a potent inhibitor of renin which demonstrated hypotensive activity in a salt depleted monkey.

Amino Acid Sequence↗
PubMed1986

Comparative structural anatomy of the complement anaphylatoxin proteins C3a, C4a and C5a.

The anaphylatoxins are a family of proteins produced during the course of complement activation as the result of cleavage by specific serine proteases. These proteins are involved in a variety of biological functions, including inflammation. Comparative modeling techniques have been used to produce structures for C4a and C5a from the crystal structure of C3a. All three structures have conserved interior residues but very different external side chains and surface shapes and properties. Comparison of the anaphylatoxin structures and of the sequence conservation among different species suggests possible locations for their receptor binding sites and for their specificity residues which permit regulated proteolytic cleavage from precursor.

Amino Acid Sequence↗
PubMed1985

Model structure for the inflammatory protein C5a.

The complement cleavage product C5a is a potent stimulant of inflammatory processes; thus, inhibition of C5a activity is of therapeutic interest. The three-dimensional structure of the major portion of C5a was modeled from the homologous C3a crystal structure by comparative modeling techniques. The model shows that core residues of C5a are completely conserved, while external residues differ from C3a. Even though the amino-terminal 12 residues of C3a are disordered in the crystal, this sequence in C5a may form an amphipathic helix. The distribution of species sequence differences in the complete C5a structure suggests a possible receptor binding site.

Amino Acid Sequence↗
PubMed1984

Structure of haptoglobin and the haptoglobin-hemoglobin complex by electron microscopy.

The human serum protein, haptoglobin, forms a stable, irreversible complex with hemoglobin. Haptoglobin is composed of two H chains, which are connected via two smaller L chains to give a protein of 85,000 Mr. In the complex, each H chain binds an alpha beta dimer of hemoglobin for a total molecular weight of 150,000. The scanning transmission electron microscope has been used to derive new information about the shape and structure of haptoglobin and hemoglobin, and about their relative orientation in the complex. The micrographs of negatively stained images show that haptoglobin has the shape of a barbell with two spherical head groups, which are the H chains. These are connected by a thin filament with a central knob, which corresponds to the L chains. The overall length of the molecule is about 124(+/- 8) A and the interhead distance is 87 (+/- 7) A. In the haptoglobin-hemoglobin complex, the head groups are ellipsoidal and under optimal staining conditions bilobal . Thus, the alpha beta dimers are binding to the H chains, but off the long axis of the barbell by 127 degrees in a trans configuration. This angle considerably restricts the region on the surface of the H chain structure that can contain the hemoglobin binding site. The interhead group distance for complex is 116.5(+/- 6.3) A or 30 A greater than for haptoglobin. The N terminus of the beta chain was located on the trans off-axis configured barbell structure of complex by using a hemoglobin that was crosslinked between the alpha beta dimers in the region of the beta N terminus. The distances and angles that are measured on the micrographs for the native and crosslinked complex molecules permit the directions of two of the alpha beta dimer ellipsoid axes to be assigned. Taken together, these data provide an approximate relative orientation for the binding of the alpha beta dimer to the H chain of haptoglobin.

Binding Sites↗
PubMed1984

Structure and assembly of haptoglobin polymers by electron microscopy.

Haptoglobin (Hp) consists of light (L) and heavy (H) chains, the latter of which combine with hemoglobin alpha beta dimers to form a highly stable complex. Human haptoglobin assembles as HL units that occur in two allelic forms; HL1 , which is monovalent, and HL2 , which is divalent. As a result, three phenotypic forms exist in the human population: Hp1-1, the homozygous form in which the monovalent HL1 unit occurs as a dimer; Hp2-2, the homozygous form of the divalent HL2 unit, which gives a series of polymers; and the heterozygous Hp2-1 form, which gives a different series of polymers. We have investigated the structures and assembly properties of these two haptoglobin polymeric series in their complexes with hemoglobin using high-resolution scanning transmission electron microscopy. Polymers of complex are composed of ellipsoidal or bilobal head groups, which are the H alpha beta subunits connected by thin filament-like structures, which are the L chains. Polymers of size up to pentamers can be identified easily by counting the number of head groups in the molecule. Complex 2-1 and complex 2-2 trimers were studied extensively. The differences in detailed morphology show that while the 2-1 trimer is a linear polymer, the 2-2 trimer is a closed circular molecule. The micrograph images suggest that complex 2-2 tetramers and pentamers, and perhaps higher forms may also be cyclic. The structure of the L2 subunit of haptoglobin is shown to be composed of two domains, which may be similar in structure to the single domain of the monovalent L1 chain. The two L2 domains are connected by a hinge that has quite limited flexibility. Using these structural models, assembly characteristics and structural properties of the trimers and tetramers of complex 2-1 and complex 2-2 are described.

Biopolymers↗
PubMed1984

Photocephalometry: errors of projection and landmark location.

A method called photocephalometry was recently described for the possible soft-tissue evaluation of orthognathic surgery patients by the superimposition of coordinated cephalographs and photographs. A grid analysis was performed to determine the accuracy of the superimposition method. In addition, the reliability of landmark identification was analyzed by the method error of Baumrind and Frantz, using three replicates of twelve patients' photographs. Comparison of twenty-one grid intervals showed that the magnification of the photographic image for any given grid plane is not correlated to that of the radiographic image. Accurate comparisons between soft- and hard-tissue anatomy by simply superimposing the images are not feasible because of the difference in the enlargement factors between the photographs and x-ray films. As was noted by Baumrind and Frantz, a wide range exists in the variability of estimating the location of landmarks. Sixty-six percent of the lateral photographic landmarks and 57% of the frontal landmarks had absolute mean errors for all twelve patients that were less than or equal to 2.0 mm. In general, the envelope of error for most landmarks was not circular. Although the photocephalometric apparatus as described by Hohl and colleagues does not yield the desired quantitative correlation between hard and soft tissues, valuable quantitative information on soft tissue can be easily obtained with the standardization and replication possible with the camera setup and enlarged photographs.

Adult↗
PubMed1984

Preparation and properties of nickel hemoglobin.

Hemoglobin A reconstituted with nickel protoporphyrin IX (NiHbA) has been prepared and characterized. Kinetics of its reaction with p-mercuribenzoate and with haptoglobin, absorption and circular dichroism spectra, and x-ray crystallographic properties have been investigated as probes of its structural conformation. The results suggest that NiHbA exists in a structure that is similar to the deoxy, or T-state of HbA. It is proposed that NiHbA and its derivatives may serve as a useful model for future studies of hemoglobin allosteric changes.

Crystallization↗
PubMed1983

Hemoglobin-binding site on haptoglobin probed by selective proteolysis.

Selective proteolysis has been used to delineate the hemoglobin-binding site on haptoglobin heavy chain. Haptoglobin was cleaved specifically by plasmin, trypsin, chymotrypsin, staphylococcal protease, and thermolysin. Haptoglobin-hemoglobin complex was treated with these enzymes to determine which sites were protected from cleavage by the hemoglobin. The modified haptoglobins were tested for changes in their hemoglobin and hemoglobin alpha chain-binding properties. The sites of proteolytic cleavage were identified from the newly generated NH2 termini by automated Edman degradation amino acid-sequencing techniques. The results suggest that residues 128 through 131, 136 and 137, as well as 9 and 10 of the heavy chain may be involved in the binding of hemoglobin. On the other hand, residues 159 and 160, which lie in the 17-residue additional loop that is unique to haptoglobin among its homologous serine protease family, and residues 73 and 74, which lie close to the carbohydrate-binding residues, appear to be remote from the hemoglobin-binding site.

Amino Acid Sequence↗
PubMed1980

Model for haptoglobin heavy chain based upon structural homology.

A model has been constructed for haptoglobin heavy chain by using the known sequence homology to the mammalian serine proteases. The three-dimensional structures for three serine proteases, chymotrypsin, trypsin, and elastase, were compared and the structural features that are conserved in all three were extracted. The haptoglobin heavy chain sequence was aligned to the sequences of the three serine proteases by maximizing sequence homology in the regions of conserved structure. The resulting alignment shows that haptoglobin heavy chain must be very closely homologous to these proteases in structure as well as in sequence. Coordinates were derived for the heavy chain by using the homologous structures. The problems associated with these coordinates are outlined and methods for solving them are indicated. The features of the haptoglobin heavy chain structure are described. Implications of the structure for the very strong interaction between this subunit and hemoglobin are discussed.

Amino Acid Sequence↗
PubMed1978

Macromolecular shape and surface maps by solvent exclusion.

A quantitative function equivalent to the "molecular" surface proposed by F. M. Richards [(1977) Annu. Rev. Biophys. Bioeng. 6, 151--176] is defined by the closest approach of solvent spheres to a macromolecule. The function can be used to visualize surface topography, polarity, and charge either as a three-dimensional net or by mapping onto a plane; to calculate surface areas; and to demarcate complementary sites in contacts between subunits. Applications to shape-specific recognition in protein structure and aggregation are discussed.

Methemoglobin↗