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PDBsum entry 3e3f
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References listed in PDB file
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Key reference
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Title
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Evidence for a bicarbonate "escort" site in haemophilus influenzae beta-Carbonic anhydrase .
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Authors
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R.S.Rowlett,
K.M.Hoffmann,
H.Failing,
M.M.Mysliwiec,
D.Samardzic.
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Ref.
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Biochemistry, 2010,
49,
3640-3647.
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PubMed id
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Abstract
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The Haemophilus influenzae beta-carbonic anhydrase (HICA) allosteric site
variants V47A and G41A were overexpressed and purified to homogeneity. These
variants have k(cat)/K(m) values similar to that of the wild-type enzyme and
exhibit a similar dramatic decrease in catalytic activity at pH <8.0.
However, both HICA-G41A and -V47A were serendipitously found to bind sulfate ion
or bicarbonate ion near pairs of Glu50 and Arg64 residues located on the
dimerization interface. In the case of HICA-V47A, bicarbonate ions
simultaneously bind to both the dimerization interface and the allosteric sites.
For HICA-G41A, two of 12 chains in the asymmetric unit bind bicarbonate ion
exclusively at the dimerization interface, while the remaining 10 chains bind
bicarbonate ion exclusively at the allosteric site. We propose that the new
anion binding site along the dimerization interface of HICA is an "escort" site
that represents an intermediate along the ingress and egress route of
bicarbonate ion to and from the allosteric binding site, respectively. The
structural evidence for sulfate binding at the escort site suggests that the
mechanism of sulfate activation of HICA is the result of sulfate ion competing
for bicarbonate at the escort site, preventing passage of bicarbonate from the
bulk solution to its allosteric site.
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