A disulfide bridge allows for site-selective binding in liver bile acid binding protein thereby stabilising the orientation of key amino acid side chains.
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 GCDA [corrected] and GCA [corrected] 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.
Laboratorio NMR, ISMAC-CNR, Via Bassini 15, 20133 Milano, Italy.
Simona
S
Tomaselli
Michael
M
Assfalg
Katiuscia
K
Pagano
Clelia
C
Cogliati
Serena
S
Zanzoni
Henriette
H
Molinari
Laura
L
Ragona
D000596:Amino Acids / Q000737:chemistry*; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry*; D006801:Humans; D008099:Liver / Q000737:chemistry*; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular
D000596:Amino Acids; D002352:Carrier Proteins; D004220:Disulfides; D008562:Membrane Glycoproteins; C037643:bile acid binding proteins