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  • Title: Population shift vs induced fit: the case of bovine seminal ribonuclease swapping dimer.
    Author: Merlino A, Vitagliano L, Sica F, Zagari A, Mazzarella L.
    Journal: Biopolymers; 2004 Apr 15; 73(6):689-95. PubMed ID: 15048772.
    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.
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