Jacobson G R, Saraceni-Richards C
Department of Biology, Boston University, Massachusetts 02215.
J Bioenerg Biomembr. 1993 Dec;25(6):621-6. doi: 10.1007/BF00770249.
The bacterial phosphoenolpyruvate-dependent carbohydrate phosphotransferase system (PTS) consists of several proteins whose primary functions are to transport and phosphorylate their substrates. The complexity of the PTS undoubtedly reflects its additional roles in chemotaxis to PTS substrates and in regulation of other metabolic processes in the cell. The PTS permeases (Enzymes II) are the membrane-associated proteins of the PTS that sequentially recognize, transport, and phosphorylate their specific substrates in separate steps, and the Escherichia coli mannitol permease is one of the best studied of these proteins. It consists of two cytoplasmic domains (EIIA and EIIB) involved in mannitol phosphorylation and an integral membrane domain (EIIC) which is sufficient to bind mannitol, but which transports mannitol at a rate that is dependent on phosphorylation of the EIIA and EIIB domains. Recent results show that several residues in a hydrophilic, 85-residue segment of the EIIC domain are important for the binding, transport, and phosphorylation of mannitol. This segment may be at least partially exposed to the cytoplasm of the cell. A model is proposed in which this region of the EIIC domain is crucial in coupling phosphorylation of the EIIB domain to transport through the EIIC domain of the mannitol permease.
细菌磷酸烯醇丙酮酸依赖性碳水化合物磷酸转移酶系统（PTS）由几种蛋白质组成，其主要功能是转运底物并使其磷酸化。PTS的复杂性无疑反映了它在对PTS底物的趋化作用以及细胞内其他代谢过程调控中的额外作用。PTS通透酶（酶II）是PTS的膜相关蛋白，它们在不同步骤中依次识别、转运并磷酸化其特定底物，大肠杆菌甘露醇通透酶就是这些蛋白中研究得较为透彻的一种。它由两个参与甘露醇磷酸化的胞质结构域（EIIA和EIIB）和一个完整的膜结构域（EIIC）组成，EIIC足以结合甘露醇，但其转运甘露醇的速率取决于EIIA和EIIB结构域的磷酸化。最近的研究结果表明，EIIC结构域中一个85个残基的亲水区段中的几个残基对甘露醇的结合、转运和磷酸化至关重要。该片段可能至少部分暴露于细胞的细胞质中。本文提出了一个模型，其中EIIC结构域的这一区域在将EIIB结构域的磷酸化与通过甘露醇通透酶的EIIC结构域的转运相偶联方面起着关键作用。
