Akiyama Nobuhiko, Takeda Kazuki, Miki Kunio
Department of Chemistry, Kyoto University, Sakyo-ku, Japan.
J Mol Biol. 2009 Sep 25;392(3):559-65. doi: 10.1016/j.jmb.2009.07.043. Epub 2009 Jul 22.
Lactate is utilized in many biological processes, and its transport across biological membranes is mediated with various types of transporters. Here, we report the crystal structures of a lactate-binding protein of a TRAP (tripartite ATP-independent periplasmic) secondary transporter from Thermus thermophilus HB8. The folding of the protein is typical for a type II periplasmic solute-binding protein and forms a dimer in a back-to-back manner. One molecule of l-lactate is clearly identified in a cleft of the protein as a complex with a calcium ion. Detailed crystallographic and biochemical analyses revealed that the calcium ion can be removed from the protein and replaced with other divalent cations. This characterization of the structure of a protein binding with calcium lactate makes a significant contribution to our understanding of the mechanisms by which calcium and lactate are accommodated in cells.
乳酸参与多种生物过程，其跨生物膜的转运由多种类型的转运蛋白介导。在此，我们报道了嗜热栖热菌HB8的一种TRAP（三部分ATP非依赖性周质）次级转运蛋白的乳酸结合蛋白的晶体结构。该蛋白的折叠对于II型周质溶质结合蛋白来说是典型的，并以背对背的方式形成二聚体。在蛋白的裂隙中清晰地鉴定出一分子L-乳酸与一个钙离子形成的复合物。详细的晶体学和生化分析表明，钙离子可从蛋白中去除并被其他二价阳离子取代。这种与乳酸钙结合的蛋白结构特征，对我们理解细胞中钙和乳酸的容纳机制有重要贡献。
