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PDBsum entry 2v6a
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Oxidoreductase
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PDB id
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2v6a
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Contents |
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(+ 2 more)
467 a.a.
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(+ 2 more)
140 a.a.
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References listed in PDB file
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Key reference
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Title
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Structural analysis of altered large-Subunit loop-6/carboxy-Terminus interactions that influence catalytic efficiency and co2/o2 specificity of ribulose-1,5-Bisphosphate carboxylase/oxygenase.
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Authors
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S.Karkehabadi,
S.Satagopan,
T.C.Taylor,
R.J.Spreitzer,
I.Andersson.
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Ref.
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Biochemistry, 2007,
46,
11080-11089.
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PubMed id
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Note: In the PDB file this reference is
annotated as "TO BE PUBLISHED". The citation details given above have
been manually determined.
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Abstract
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The loop between alpha-helix 6 and beta-strand 6 in the alpha/beta-barrel of
ribulose-1,5-bisphosphate carboxylase/oxygenase plays a key role in
discriminating between CO2 and O2. Genetic screening in Chlamydomonas
reinhardtii previously identified a loop-6 V331A substitution that decreases
carboxylation and CO2/O2 specificity. Revertant selection identified T342I and
G344S substitutions that restore photosynthetic growth by increasing
carboxylation and specificity of the V331A enzyme. In numerous X-ray crystal
structures, loop 6 is closed or open depending on the activation state of the
enzyme and the presence or absence of ligands. The carboxy terminus folds over
loop 6 in the closed state. To study the molecular basis for catalysis, directed
mutagenesis and chloroplast transformation were used to create T342I and G344S
substitutions alone. X-ray crystal structures were then solved for the V331A,
V331A/T342I, T342I, and V331A/G344S enzymes, as well as for a D473E enzyme
created to assess the role of the carboxy terminus in loop-6 closure. V331A
disturbs a hydrophobic pocket, abolishing several van der Waals interactions.
These changes are complemented by T342I and G344S, both of which alone cause
decreases in CO2/O2 specificity. In the V331A/T342I revertant enzyme, Arg339
main-chain atoms are displaced. In V331A/G344S, alpha-helix 6 is shifted. D473E
causes disorder of the carboxy terminus, but loop 6 remains closed. Interactions
between a transition-state analogue and several residues are altered in the
mutant enzymes. However, active-site Lys334 at the apex of loop 6 has a normal
conformation. A variety of subtle interactions must be responsible for catalytic
efficiency and CO2/O2 specificity.
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