當(dāng)一個自己喜歡的碳來源存在時,，細(xì)菌會利用一個被稱為“碳分解代謝物抑制”(CCR) 的系統(tǒng)來使在對自己不太喜歡的碳來源的利用中所涉及的蛋白的合成和活動停止。在大腸桿菌中,，葡萄糖特定的磷酸轉(zhuǎn)移酶系統(tǒng) enzyme IIA (EIIAGlc)是這一控制系統(tǒng)的核心,；當(dāng)環(huán)境中有葡萄糖時，其他糖（如麥芽糖）的運輸便會被停止,。這篇論文報告了結(jié)合到MalFGK2麥芽糖運輸?shù)鞍咨系囊粋€EIIAGlc的X-射線晶體結(jié)構(gòu),。該結(jié)構(gòu)顯示，兩個EIIAGlc分子結(jié)合到該麥芽糖運輸?shù)鞍椎陌|(zhì)ATP酶亞單元上，在一個朝里的構(gòu)形中使其穩(wěn)定,，阻止發(fā)生ATP水解所需的結(jié)構(gòu)重排,，同時也阻止麥芽糖的運輸。（生物谷Bioon.com）
生物谷推薦英文摘要：
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.
