Domain Structure and Conformation of Histidine−Proline-Rich Glycoprotein,

• DOI: 10.1021/bi952061t
• Publication Date: 2002-07-26T05:13:40Z
• Authors: Dorin-Bogdan Borza; Fred M. Tatum; William T. Morgan
• Keywords: Polyproline helix; Random coil

The complete primary structure of rabbit plasma histidine−proline-rich glycoprotein (HPRG), also known as histidine-rich glycoprotein, was determined by a combination cDNA and peptide sequencing. Limited proteolysis with plasmin yielded three disulfide-linked fragments that were further purified. Reduction the disulfide bonds dithiothreitol under nondenaturing conditions releases central, domain, which contains 15 tandem repeats pentapeptide [H/P][H/P]PHG. N-terminal fragment (295 amino acids), consisting two cystatin-like modules, is bound to proline-rich C-terminal (105 acids) via buried bond whose reduction requires prior denaturation. Far-UV circular dichroism spectra revealed β-sheet some α-helix, polyproline-II helix, random coil in secondary N-terminal, domains, respectively. modular architecture HPRG suggests it may have several independent binding sites its biological role be bring or more ligands together. 34 53 histidine residues HPRG, binds heparin has an isoelectric point 7.15 relatively high apparent pKa (7.0) residues, thus probably mediates interaction between heparin, strikingly sensitive pH range 7.0−7.4 [Peterson et al. (1987) J. Biol. Chem. 262, 7567−7574]. Solvent perturbation second-derivative UV spectroscopy changes environment tryptophan upon lowering pH. This transition had midpoint at 6.0 required bridging domain N/C fragment. data are consistent mutual repulsion protonated region causing conformational change transmitted rest molecule bond.