Andrews FH, Rogers MP, Paul LN, McLeish MJ. Perturbation of the monomer-monomer interfaces of the benzoylformate decarboxylase tetramer.
Biochemistry 2014;
53:4358-67. [PMID:
24956165 PMCID:
PMC4215898 DOI:
10.1021/bi500081r]
[Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
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The X-ray structure of benzoylformate
decarboxylase (BFDC) from Pseudomonas putida ATCC
12633 shows it to be a tetramer.
This was believed to be typical of all thiamin diphosphate-dependent
decarboxylases until recently when the structure of KdcA, a branched-chain
2-keto acid decarboxylase from Lactococcus lactis, showed it to be a homodimer. This lent credence to earlier unfolding
experiments on pyruvate decarboxylase from Saccharomyces cerevisiae that indicated that it might be active as a dimer. To investigate
this possibility in BFDC, we sought to shift the equilibrium toward
dimer formation. Point mutations were made in the noncatalytic monomer–monomer
interfaces, but these had a minimal effect on both tetramer formation
and catalytic activity. Subsequently, the R141E/Y288A/A306F variant
was shown by analytical ultracentrifugation to be partially dimeric.
It was also found to be catalytically inactive. Further experiments
revealed that just two mutations, R141E and A306F, were sufficient
to markedly alter the dimer–tetramer equilibrium and to provide
an ∼450-fold decrease in kcat.
Equilibrium denaturation studies suggested that the residual activity
was possibly due to the presence of residual tetramer. The structures
of the R141E and A306F variants, determined to <1.5 Å resolution,
hinted that disruption of the monomer interfaces will be accompanied
by movement of a loop containing Leu109 and Leu110. As these residues
contribute to the hydrophobicity of the active site and the correct
positioning of the substrate, it seems that tetramer formation may
well be critical to the catalytic activity of BFDC.
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