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A Disulfide Bridge Allows for Site‐Selective Binding in Liver Bile Acid Binding Protein Thereby Stabilising the Orientation of Key Amino Acid Side Chains
Author(s) -
Tomaselli Simona,
Assfalg Michael,
Pagano Katiuscia,
Cogliati Clelia,
Zanzoni Serena,
Molinari Henriette,
Ragona Laura
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102203
Subject(s) - side chain , hydrogen bond , histidine , glycocholic acid , chemistry , intramolecular force , stereochemistry , binding site , ligand (biochemistry) , disulfide bond , amino acid , biochemistry , bile acid , crystallography , molecule , receptor , organic chemistry , cholic acid , polymer
The presence of a disulfide bridge in liver bile acid binding protein (L‐BABP/S‐S) allows for site‐selective binding of two bile acids, glycochenodeoxycholic (GCDA) and glycocholic acid (GCA), differing only in the presence of a hydroxyl group. The protein form devoid of the disulfide bridge (L‐BABP) binds both bile salts without discriminating ability. We investigate the determinants of the molecular recognition process in the formation of the heterotypic L‐BABP/S‐S complex with GCA and GCDA located in the superficial and inner protein sites, respectively. The comparison of the NMR spectroscopy structure of heterotypic holo L‐BABP/S‐S, the first reported for this protein family, with that of the homotypic L‐BABP complex demonstrates that the introduction of a S–S link between adjacent strands changes the conformation of three key residues, which function as hot‐spot mediators of molecular discrimination. The favoured χ 1 rotameric states (t, g + and g − for E99, Q100 and E109 residues, respectively) allow the onset of an extended intramolecular hydrogen‐bond network and the consequent stabilisation of the side‐chain orientation of a buried histidine, which is capable of anchoring a specific ligand.