当一个自己喜欢的碳来源存在时，细菌会利用一个被称为“碳分解代谢物抑制”(CCR) 的系统来使在对自己不太喜欢的碳来源的利用中所涉及的蛋白的合成和活动停止。在大肠杆菌中，葡萄糖特定的磷酸转移酶系统 enzyme IIA (EIIAGlc)是这一控制系统的核心；当环境中有葡萄糖时，其他糖（如麦芽糖）的运输便会被停止。这篇论文报告了结合到MalFGK2麦芽糖运输蛋白上的一个EIIAGlc的X-射线晶体结构。该结构显示，两个EIIAGlc分子结合到该麦芽糖运输蛋白的胞质ATP酶亚单元上，在一个朝里的构形中使其稳定，阻止发生ATP水解所需的结构重排，同时也阻止麦芽糖的运输。（生物谷Bioon.com）
生物谷推荐英文摘要：
Nature doi:10.1038/nature12232
Carbon catabolite repression of the maltose transporter revealed by X-ray crystallography
Shanshuang Chen, Michael L. Oldham, Amy L. Davidson& Jue Chen
Efficient carbon utilization is critical to the survival of microorganisms in competitive environments. To optimize energy usage,bacteria have developed an integrated control system to preferentially uptake carbohydrates that support rapid growth. The availability of a preferred carbon source, such as glucose, represses the synthesis and activities of proteins necessary for the transport and metabolism of secondary carbon sources. This regulatory phenomenon is defined as carbon catabolite repression. In enteric bacteria, the key player of carbon catabolite repression is a component of the glucose-specific phosphotransferase system, enzyme IIA (EIIAGlc）.It is known that unphosphorylated EIIAGlc binds to and inhibits a variety of transporters when glucose is available. However, understanding the underlying molecular mechanism has been hindered by the complete absence of structures for any EIIAGlc–transporter complexes. Here we present the 3.9 A crystal structure of Escherichia coli EIIAGlc in complex with the maltose transporter, an ATP-binding cassette (ABC) transporter. The structure shows that two EIIA Glc molecules bind to the cytoplasmic ATPase subunits, stabilizing the transporter in an inward-facing conformation and preventing the structural rearrangements necessary for ATP hydrolysis. We also show that the half-maximal inhibitory concentrations of the fulllength EIIAGlc and an amino-terminal truncation mutant differ by 60-fold, consistent with the hypothesis that the amino-terminal region, disordered in the crystal structure, functions as a membrane anchor to increase the effective EIIAGlc concentration at the membrane.Together these data suggest a model of how the central regulatoryprotein EIIAGlc allosterically inhibits maltose uptake in E. coli.
