Crystal structures of the BlaI repressor from Staphylococcus aureus and its complex with DNA:: Insights into transcriptional regulation of the bla and mec operons
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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DOI：
10.1128/jb.187.5.1833-1844.2005
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发表时间：
2005-03-01
影响因子：
3.2
通讯作者：
Archer, GL
中科院分区：
文献类型：
--
作者：
Safo, MK;Zhao, QX;Archer, GL
14-kDa BlaI蛋白抑制blaZ（编码β-内酰胺酶的基因）的转录。它与MecI同源，后者调节编码青霉素结合蛋白PBP 2a的基因mecA的表达。这些基因介导葡萄球菌对β-内酰胺类抗生素的耐药性。这两种阻遏物都可以结合bla或mec DNA启动子-操纵子序列。受调节的抗性基因通过受体介导的阻遏物裂解而被激活。当β-内酰胺抗生素结合传感器-换能器信号分子BlaRI或MecR 1的膜外传感器时，诱导裂解。来自金黄色葡萄球菌的BlaI的晶体结构，无论是游离形式还是与32 bp DNA的mec操作符的复合物，已分别确定为2.0和2.7埃分辨率。MecI的结构，也在自由的形式和复杂的bla运营商，以前已经报道。这两种阻遏物形成同源二聚体，每个单体由一个N-末端DNA结合结构域和一个C-末端二聚化结构域组成。与mec操作符复合的BlaI的结构显示了在mec和bla靶标之间保守的蛋白质-DNA界面。识别螺旋α 3与保守的TACA/TGTA DNA结合基序特异性相互作用。BlaI和可能的MecI二聚体以上下排列的方式与mec DNA双螺旋的相对面结合，而MecI和可能的BlaI二聚体与bla启动子-操纵基因DNA的相同DNA面结合。这是由于mec和bla DNA结合位点的不同间隔。此外，二聚体蛋白质的灵活性可能使C-末端蛋白水解切割位点更容易接近时，阻遏物结合到DNA比当他们在溶液中，这表明，诱导级联涉及绑定，而不是免费的阻遏物。
The 14-kDa BlaI protein represses the transcription of blaZ, the gene encoding P-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 P-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 P-lactam antibiotics bind the extramembrane sensor of the sensor-transducer signaling molecules, BlaRI 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-Angstrom 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.