Structure and substrate specificity of an SspB ortholog: Design implications for AAA plus adaptors
Structure and substrate specificity of an SspB ortholog: Design implications for AAA plus adaptors
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DOI：
10.1016/j.str.2007.08.008
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发表时间：
2007-10-01
期刊：
影响因子：
5.7
通讯作者：
Baker, Tania A.
中科院分区：
文献类型：
--
作者：
Chien, Peter;Grant, Robert A.;Baker, Tania A.
AAA+蛋白酶通常由调节蛋白质周转的空间和时间控制的衔接子调节。新月柄杆菌是一种α-变形杆菌，其需要通过AAA+ ClpXP蛋白酶降解蛋白质以进行细胞周期进程，并且含有结合ssrA标记的蛋白质并将其靶向ClpXP的衔接子（SspB α）。在这里，我们确定的标签结合特异性和晶体结构的SspBa。尽管序列同源性差，但总体SspB α折叠类似于来自其他细菌的直系同源物。然而，几个结构特征是特定于SsplB α亚家族，包括二聚化界面，优化ssrA标签递送的结合表面，以及标签结合凹槽中的残基，其充当底物识别的选择性守门人。这些残基的突变扩大了特异性，产生了一个混杂的适配器，识别扩展的底物库。这些结果突出了衔接子介导的底物识别的一般特征，并阐明了衔接子功能的设计原则。
AAA+ proteases are frequently regulated by adaptors that modulate spatial and temporal control of protein turnover. Caulobacter crescentus is an alpha-proteobacterium which requires protein degradation by the AAA+ ClpXP protease for cell-cycle progression, and contains an adaptor (SspB alpha) that binds ssrA-tagged proteins and targets them to CIpXP. Here we determine the tag-binding specificity and crystal structure of SspBa. Despite poor sequence homology, the overall SspB alpha fold resembles orthologs from other bacteria. However, several structural features are specific to the SsplB alpha subfamily, including the dimerization interface, binding surfaces optimized for ssrA-tag delivery, and residues in the tag-binding groove that act as selectivity gatekeepers for substrate recognition. Mutagenesis of these residues broadens specificity, creating a promiscuous adaptor that recognizes an expanded substrate repertoire. These results highlight general features of adaptor-mediated substrate recognition and shed light on design principles that underlie adaptor function.