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Title: Conserved Glu40 and Glu433 of the biotin carboxylase domain of yeast pyruvate carboxylase I isoenzyme are essential for the association of tetramers
Authors: Sarawut Jitrapakdee
Katharina H. Surinya
Abdussalam Adina-Zada
Steven W. Polyak
Cvetan Stojkoski
Roger Smyth
Grant W. Booker
W. Wallace Cleland
Paul V. Attwood
John C. Wallace
Mahidol University
University of Adelaide
University of Western Australia
University of Wisconsin Madison, Institute for Enzyme Research
Keywords: Biochemistry, Genetics and Molecular Biology
Issue Date: 11-Sep-2007
Citation: International Journal of Biochemistry and Cell Biology. Vol.39, No.11 (2007), 2120-2134
Abstract: The native form of pyruvate carboxylase is an α4tetramer but the tetramerisation domain of each subunit is currently unknown. To identify this domain we co-expressed yeast pyruvate carboxylase 1 isozyme (Pyc1) with an N-terminal myc tag, together with constructs encoding either the biotin carboxylase (BC) domain or the transcarboxylase-biotin carboxyl carrier domain (TC-BCC), each with an N-terminal 9-histidine tag. From tag-affinity chromatography experiments, the subunit contacts within the tetramer were identified to be primarily located in the 55 kDa BC domain. From modelling studies based on known structures of biotin carboxylase domains and subunits we have predicted that Arg36 and Glu433 and Glu40 and Lys426, respectively, are involved pairwise in subunit interactions and are located on opposing subunits in the putative subunit interface of Pyc1. Co-expression of mutant forms with wild type Pyc1 showed that the R36E mutation had no effect on the interaction of these subunits with those of wild type Pyc1, while the E40R, E433R and R36E:E433R mutations caused severe loss of interaction with wild type Pyc1. Ultracentrifugal analysis of these mutants when expressed and purified separately indicated that the predominant form of E40R, E433R and R36R:E433R mutants is the monomer, and that their specific activities are less than 2% of the wild type. Studies on the association state and specific activity of the R36E mutant at different concentrations showed it to be much more susceptible to tetramer dissociation and inactivation than the wild type. Our results suggest that Glu40 and Glu433 play essential roles in subunit interactions.
ISSN: 13572725
Appears in Collections:Scopus 2006-2010

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