A Disulfide Bridge Allows for Site-Selective Binding in Liver Bile Acid Binding Protein Thereby Stabilising the Orientation of Key Amino Acid Side Chains

作者：Tomaselli Simona; Assfalg Michael; Pagano Katiuscia; Cogliati Clelia; Zanzoni Serena; Molinari Henriette^*; Ragona Laura

来源：Chemistry - A European Journal, 2012, 18(10): 2857-2866.

DOI：10.1002/chem.201102203

• heterotypic complexes
• molecular recognition
• NMR spectroscopy
• proteins
• site selectivity

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 SS link between adjacent strands changes the conformation of three key residues, which function as hot-spot mediators of molecular discrimination. The favoured ?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.

• 出版日期2012-3