Ligation tunes protein reactivity in an ancient haemoglobin: kinetic evidence for an allosteric mechanism in Methanosarcina acetivorans protoglobin |
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Authors: | Abbruzzetti Stefania Tilleman Lesley Bruno Stefano Viappiani Cristiano Desmet Filip Van Doorslaer Sabine Coletta Massimo Ciaccio Chiara Ascenzi Paolo Nardini Marco Bolognesi Martino Moens Luc Dewilde Sylvia |
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Affiliation: | Dipartimento di Fisica, Università degli Studi di Parma, Parma, Italy. |
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Abstract: | Protoglobin from Methanosarcina acetivorans (MaPgb) is a dimeric globin with peculiar structural properties such as a completely buried haem and two orthogonal tunnels connecting the distal cavity to the solvent. CO binding to and dissociation from MaPgb occur through a biphasic kinetics. We show that the heterogenous kinetics arises from binding to (and dissociation from) two tertiary conformations in ligation-dependent equilibrium. Ligation favours the species with high binding rate (and low dissociation rate). The equilibrium is shifted towards the species with low binding (and high dissociation) rates for the unliganded molecules. A quantitative model is proposed to describe the observed carbonylation kinetics. |
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