Publication: Coordinating role of His216 in MgATP binding and cleavage in pyruvate carboxylase
Issued Date
2014-02-18
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15204995
00062960
00062960
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2-s2.0-84894285445
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Mahidol University
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SCOPUS
Bibliographic Citation
Biochemistry. Vol.53, No.6 (2014), 1051-1058
Suggested Citation
Abdussalam Adina-Zada, Sarawut Jitrapakdee, John C. Wallace, Paul V. Attwood Coordinating role of His216 in MgATP binding and cleavage in pyruvate carboxylase. Biochemistry. Vol.53, No.6 (2014), 1051-1058. doi:10.1021/bi4016814 Retrieved from: https://repository.li.mahidol.ac.th/handle/123456789/33300
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Title
Coordinating role of His216 in MgATP binding and cleavage in pyruvate carboxylase
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Abstract
His216 is a well-conserved residue in pyruvate carboxylases and, on the basis of structures of the enzyme, appears to have a role in the binding of MgATP, forming an interaction with the 3′-hydroxyl group of the ribose ring. Mutation of this residue to asparagine results in a 9-fold increase in the Kmfor MgATP in its steady-state cleavage in the absence of pyruvate and a 3-fold increase in the Kmfor MgADP in its steady-state phosphorylation by carbamoyl phosphate. However, from single-turnover experiments of MgATP cleavage, the Kdof the enzyme·MgATP complex is essentially the same in the wild-type enzyme and H216N. Direct stopped-flow measurements of nucleotide binding and release using the fluorescent analogue FTP support these observations. However, the first-order rate constant for MgATP cleavage in the single-turnover experiments in H216N is only 0.75% of that for the wild-type enzyme, and thus, the MgATP cleavage step is rate-limiting in the steady state for H216N but not for the wild-type enzyme. Close examination of the structure of the enzyme suggested that His216 may also interact with Glu218, which in turn interacts with Glu305 to form a proton relay system involved in the deprotonation of bicarbonate. Single-turnover MgATP cleavage experiments with mutations of these two residues resulted in kinetic parameters similar to those observed in H216N. We suggest that the primary role of His216 is to coordinate the binding of MgATP and the deprotonation of bicarbonate in the reaction to form the putative carboxyphosphate intermediate by participation in a proton relay system involving Glu218 and Glu305. © 2014 American Chemical Society.