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J Greer

Publications and source records attributed to J Greer.

At least 73 records · Page 4Linked to original sources
PubMed1982

Hemoglobin binding site and its relationship to the serine protease-like active site of haptoglobin.

Haptoglobin forms a stable, irreversible complex with hemoglobin. The H chain of haptoglobin, which is the subunit that binds hemoglobin, shows strong sequence homology with the serine protease family. This raises the question of whether hemoglobin binds to the protease-like active site pocket of H chain as the protease inhibitors do with serine proteases. This question can be tested by binding proflavin and thionin to haptoglobin because these dyes are known to interact specifically with serine proteases at the peptide binding site. A single, specific binding site, characteristic of the serine proteases, was found for haptoglobin with association constants for proflavin or 1.4 x 10(3) at pH 7.1 and 8.2 x 10(3) at pH 9.5 and for thionin of 3.5 x 10(3) at pH 7.1. In order to confirm that these dyes are indeed binding to the specificity pocket of haptoglobin, competition experiments with classical serine protease substrates and inhibitors were performed. The results showed that trypsin-specific substrates and inhibitors did compete with proflavin binding, as expected from the homology, and that reagents of a chymotryptic specificity did not. When the dye titrations were performed on haptoglobin-hemoglobin complex, the same binding constants were obtained as for haptoglobin alone. This demonstrates that the active site-like region of haptoglobin and the hemoglobin binding site are mutually exclusive and do not interact in any way.

Binding Sites↗
PubMed1982

Nature of the riboflavin interaction with the immunoglobulin IgGGAR: analogue binding studies.

The human immunoglobulin IgGGAR has been shown to bind riboflavin both in vivo and in vitro with a high binding constant [Farhangi & Osserman (1976), New Engl. J. Med. 294, 177-183; Chang et al. (1981b), Biochemistry 20, 2916-2921; Chang et al. (1981a), Biochemistry 20, 2922-2926] and, therefore, represents a natural human antibody hapten complex. In this study, the parts of the riboflavin molecule which are in intimate contact with the binding pocket have been identified, using a variety of riboflavin analogues. The binding constants of IgGGAR for these flavins were measured by fluorescence spectroscopy. The relative affinities indicate that the pyrimidine edge of the isoalloxazine interacts intimately with the combining site, particularly around N-3. The ribityl side chain and the dimethylbenzene edge of the flavin ring are not critical to the binding interaction and are probably exposed to solvent. Analogues of riboflavin with altered electronic structures have somewhat lowered affinities for IgGGAR, suggesting that the isoalloxazine ring forms stacking interactions. Comparison with other known flavin-binding proteins shows that IgGGAR binds riboflavin in a new way that is different from the sites in other proteins. The isoalloxazine ring binds similarly to the FMN-binding proteins; however, unlike virtually all the other proteins, the ribityl side chain is not essential to binding.

Antibodies, Monoclonal↗
PubMed1981

Haptoglobin-hemoglobin complex. Subunit interaction probed by cross-linking.

Haptoglobin-hemoglobin complex has been cross-linked using the bifunctional reagent 1,5-difluoro-2,4-dinitrobenzene. Sodium dodecyl sulfate-acrylamide gel electrophoresis indicated that specific cross-linking was obtained between haptoglobin H chain and a hemoglobin chain. The cross-linked complex was reduced and denatured, and the cross-linked subunits were separated from the unreacted haptoglobin and hemoglobin chains by molecular sieve chromatography. Peptide analysis on the purified cross-linked subunits showed that haptoglobin H chain was cross-linked to hemoglobin beta chain only. This result indicates that the H and beta chains are in close proximity in the haptoglobin-hemoglobin complex.

Amino Acids↗
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↗