title: Population shift vs induced fit: the case of bovine seminal ribonuclease swapping dimer.
abstract: Bovine seminal ribonuclease (BS-RNase) is a unique member of the pancreatic-like ribonuclease superfamily. This enzyme exists as two conformational isomers with distinctive biological properties. The structure of the major isomer is characterized by the swapping of the N-terminal segment (MxM BS-RNase). In this article, the crystal structures of the ligand-free MxM BS-RNase and its complex with 2'-deoxycitidylyl(3',5')-2'-deoxyadenosine derived from isomorphous crystals have been refined. Interestingly, the comparison between this novel ligand-free form and the previously published sulfate-bound structure reveals significant differences. In particular, the ligand-free MxM BS-RNase is closer to the structure of MxM BS-RNase productive complexes than to the sulfate-bound form. These results reveal that MxM BS-RNase presents a remarkable flexibility, despite the structural constraints of the interchain disulfide bridges and the swapping of the N-terminal helices. These findings have important implications to the ligand binding mechanism of MxM BS-RNase. Indeed, a population shift rather than a substrate-induced conformational transition may occur in the MxM BS-RNase ligand binding process.
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Napoli Federico II, Via Cynthia, 80126 Napoli, Italy.
authors.forename: Antonello
authors.initials: A
authors.lastname: Merlino
authors.forename: Luigi
authors.initials: L
authors.lastname: Vitagliano
authors.forename: Filomena
authors.initials: F
authors.lastname: Sica
authors.forename: Adriana
authors.initials: A
authors.lastname: Zagari
authors.forename: Lelio
authors.initials: L
authors.lastname: Mazzarella
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D018360:Crystallography, X-Ray; D019281:Dimerization; D004722:Endoribonucleases / Q000737:chemistry*; D008958:Models, Molecular; D020836:Protein Structure, Quaternary
chemical_list: D004722:Endoribonucleases; C032523:ribonuclease SPL