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PDBsum entry 1uzh
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Contents |
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(+ 2 more)
465 a.a.
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(+ 2 more)
122 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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Chimeric small subunits influence catalysis without causing global conformational changes in the crystal structure of ribulose-1,5-Bisphosphate carboxylase/oxygenase.
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Authors
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S.Karkehabadi,
S.R.Peddi,
M.Anwaruzzaman,
T.C.Taylor,
A.Cederlund,
T.Genkov,
I.Andersson,
R.J.Spreitzer.
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Ref.
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Biochemistry, 2005,
44,
9851-9861.
[DOI no: ]
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PubMed id
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Abstract
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Comparison of subunit sequences and X-ray crystal structures of
ribulose-1,5-bisphosphate carboxylase/oxygenase indicates that the loop between
beta-strands A and B of the small subunit is one of the most variable regions of
the holoenzyme. In prokaryotes and nongreen algae, the loop contains 10
residues. In land plants and green algae, the loop is comprised of approximately
22 and 28 residues, respectively. Previous studies indicated that the longer
betaA-betaB loop was required for the assembly of cyanobacterial small subunits
with plant large subunits in isolated chloroplasts. In the present study,
chimeric small subunits were constructed by replacing the loop of the green alga
Chlamydomonas reinhardtii with the sequences of Synechococcus or spinach. When
these engineered genes were transformed into a Chlamydomonas mutant that lacks
small-subunit genes, photosynthesis-competent colonies were recovered,
indicating that loop size is not essential for holoenzyme assembly. Whereas the
Synechococcus loop causes decreases in carboxylation V(max), K(m)(O(2)), and
CO(2)/O(2) specificity, the spinach loop causes complementary decreases in
carboxylation V(max), K(m)(O(2)), and K(m)(CO(2)) without a change in
specificity. X-ray crystal structures of the engineered proteins reveal
remarkable similarity between the introduced betaA-betaB loops and the
respective loops in the Synechococcus and spinach enzymes. The side chains of
several large-subunit residues are altered in regions previously shown by
directed mutagenesis to influence CO(2)/O(2) specificity. Differences in the
catalytic properties of divergent Rubisco enzymes may arise from differences in
the small-subunit betaA-betaB loop. This loop may be a worthwhile target for
genetic engineering aimed at improving photosynthetic CO(2) fixation.
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