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PDBsum entry 1sd6
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DNA binding protein
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PDB id
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1sd6
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Crystal structures of the blai repressor from staphylococcus aureus and its complex with DNA: insights into transcriptional regulation of the bla and mec operons.
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Authors
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M.K.Safo,
Q.Zhao,
T.P.Ko,
F.N.Musayev,
H.Robinson,
N.Scarsdale,
A.H.Wang,
G.L.Archer.
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Ref.
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J Bacteriol, 2005,
187,
1833-1844.
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PubMed id
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Abstract
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The 14-kDa BlaI protein represses the transcription of blaZ, the gene encoding
beta-lactamase. It is homologous to MecI, which regulates the expression of
mecA, the gene encoding the penicillin binding protein PBP2a. These genes
mediate resistance to beta-lactam antibiotics in staphylococci. Both repressors
can bind either bla or mec DNA promoter-operator sequences. Regulated resistance
genes are activated via receptor-mediated cleavage of the repressors. Cleavage
is induced when beta-lactam antibiotics bind the extramembrane sensor of the
sensor-transducer signaling molecules, BlaR1 or MecR1. The crystal structures of
BlaI from Staphylococcus aureus, both in free form and in complex with 32 bp of
DNA of the mec operator, have been determined to 2.0- and 2.7-A resolutions,
respectively. The structure of MecI, also in free form and in complex with the
bla operator, has been previously reported. Both repressors form homodimers,
with each monomer composed of an N-terminal DNA binding domain of winged
helix-turn-helix topology and a C-terminal dimerization domain. The structure of
BlaI in complex with the mec operator shows a protein-DNA interface that is
conserved between both mec and bla targets. The recognition helix alpha3
interacts specifically with the conserved TACA/TGTA DNA binding motif. BlaI and,
probably, MecI dimers bind to opposite faces of the mec DNA double helix in an
up-and-down arrangement, whereas MecI and, probably, BlaI dimers bind to the
same DNA face of bla promoter-operator DNA. This is due to the different spacing
of mec and bla DNA binding sites. Furthermore, the flexibility of the dimeric
proteins may make the C-terminal proteolytic cleavage site more accessible when
the repressors are bound to DNA than when they are in solution, suggesting that
the induction cascade involves bound rather than free repressor.
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