From the Biochemistry-Electrochemistry Research Unit, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand,
From the Biochemistry-Electrochemistry Research Unit, Institute of Science, Suranaree University of Technology, Nakhon Ratchasima 30000, Thailand.
J Biol Chem. 2018 Apr 6;293(14):5150-5159. doi: 10.1074/jbc.RA117.001012. Epub 2018 Feb 14.
Periplasmic solute-binding proteins in bacteria are involved in the active transport of nutrients into the cytoplasm. In marine bacteria of the genus , a chitooligosaccharide-binding protein (CBP) is thought to be the major solute-binding protein controlling the rate of chitin uptake in these bacteria. However, the molecular mechanism of the CBP involvement in chitin metabolism has not been elucidated. Here, we report the structure and function of a recombinant chitooligosaccharide-binding protein from , namely CBP, expressed in Isothermal titration calorimetry revealed that CBP strongly binds shorter chitooligosaccharides ((GlcNAc) , where = 2, 3, and 4) with affinities that are considerably greater than those for glycoside hydrolase family 18 and 19 chitinases but does not bind longer ones, including insoluble chitin polysaccharides. We also found that VhCBP comprises two domains with flexible linkers and that the domain-domain interface forms the sugar-binding cleft, which is not long extended but forms a small cavity. (GlcNAc) bound to this cavity, apparently triggering a closed conformation of CBP. Trp-363 and Trp-513, which stack against the two individual GlcNAc rings, likely make a major contribution to the high affinity of CBP for (GlcNAc) The strong chitobiose binding, followed by the conformational change of CBP, may facilitate its interaction with an active-transport system in the inner membrane of species.
细菌周质溶质结合蛋白参与营养物质的主动运输进入细胞质。在属的海洋细菌中，壳寡糖结合蛋白（CBP）被认为是控制这些细菌壳聚糖摄取速率的主要溶质结合蛋白。然而，CBP 参与壳聚糖代谢的分子机制尚未阐明。在这里，我们报告了表达的重组来源于的壳寡糖结合蛋白（CBP）的结构和功能， 等离了体滴定量热法显示 CBP 强烈结合较短的壳寡糖（（GlcNAc） ，其中 = 2、3 和 4），亲和力明显大于糖苷水解酶家族 18 和 19 壳聚糖酶，但不结合较长的壳寡糖，包括不溶性壳聚糖多糖。我们还发现 VhCBP 由两个具有柔性接头的结构域组成，并且结构域-结构域界面形成糖结合裂缝，该裂缝没有被长延伸，而是形成一个小空腔。（GlcNAc）结合到这个空腔中，显然触发了 CBP 的封闭构象。与两个单独的 GlcNAc 环堆叠的色氨酸 363 和色氨酸 513 可能对 CBP 对（GlcNAc）的高亲和力做出了重大贡献。强烈的二糖结合，随后是 CBP 的构象变化，可能有助于其与物种内膜中的主动运输系统相互作用。
