1] State Key Laboratory of Biomembrane and Membrane Biotechnology, School of Life Sciences, Tsinghua University, Beijing, China. [2] Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China.
1] Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing, China. [2] Ministry of Education Key Laboratory of Protein Science, School of Life Sciences, Tsinghua University, Beijing, China.
Nat Struct Mol Biol. 2015 Mar;22(3):238-41. doi: 10.1038/nsmb.2975. Epub 2015 Feb 16.
Bacteria use vitamin C (L-ascorbic acid) as a carbon source under anaerobic conditions. The phosphoenolpyruvate-dependent phosphotransferase system (PTS), comprising a transporter (UlaA), a IIB-like enzyme (UlaB) and a IIA-like enzyme (UlaC), is required for the anaerobic uptake of vitamin C and its phosphorylation to L-ascorbate 6-phosphate. Here, we present the crystal structures of vitamin C-bound UlaA from Escherichia coli in two conformations at 1.65-Å and 2.35-Å resolution. UlaA forms a homodimer and exhibits a new fold. Each UlaA protomer consists of 11 transmembrane segments arranged into a 'V-motif' domain and a 'core' domain. The V motifs form the interface between the two protomers, and the core-domain residues coordinate vitamin C. The alternating access of the substrate from the opposite side of the cell membrane may be achieved through rigid-body rotation of the core relative to the V motif.
细菌在厌氧条件下将维生素 C（L-抗坏血酸）用作碳源。依赖磷酸烯醇丙酮酸的磷酸转移酶系统（PTS），包括一个转运蛋白（UlaA）、一个 IIB 样酶（UlaB）和一个 IIA 样酶（UlaC），是厌氧摄取维生素 C 及其磷酸化为 L-抗坏血酸 6-磷酸所必需的。在这里，我们展示了来自大肠杆菌的与维生素 C 结合的 UlaA 的两种构象的晶体结构，分辨率分别为 1.65-Å 和 2.35-Å。UlaA 形成同源二聚体并呈现出新的折叠。每个 UlaA 原蛋白由 11 个跨膜片段组成，排列成“V 型结构域”和“核心”结构域。V 型结构域形成两个原蛋白之间的界面，而核心结构域残基则与维生素 C 配位。底物通过细胞膜的相对侧的交替进入可能是通过核心相对于 V 型结构域的刚体旋转来实现的。
