清华大学生命科学学院施一公教授领导的研究组合作解析了甲酸（formate）通道FocA的高分辨率结构，研究结果11月25日以Article的形式发表于Nature。
甲酸是细菌在无氧呼吸条件下的主要代谢产物之一，发酵状态下，细菌体内积聚了大量的甲酸需要穿过内膜进一步代谢。甲酸同时还是古老微生物的重要碳源之一。尽管甲酸可以透过细胞内膜，但是大量甲酸的快速运输需要转运系统。FocA是在1994年被发现的甲酸转运蛋白，属于FNT家族，可以转运甲酸、亚硝酸等短链酸。FNT家族一直以来被认为是转运蛋白(transporter)。
施一公教授研究组历时两年成功解析了FocA的高分辨率原子结构，证明FocA是通道蛋白（channel），而非转运蛋白（transporter）。更为有趣的是，尽管FocA在氨基酸序列上与水通道蛋白（aquaporin）没有任何相似性，也不具备水通道的标志性序列，但是其结构高度相似。不同的是，所有已知的aquaporin蛋白都是四聚体，而FocA以梅花状的五聚体形式存在，并且不能够通透水分子。这是首次发现与水通道结构类似但没有序列同源性的其他家族蛋白。这一发现对于研究膜蛋白的进化提供了进一步的线索。（生物谷Bioon.com）
生物谷推荐原始出处：
Nature 462, 467-472 (26 November 2009) | doi:10.1038/nature08610
Structure of the formate transporter FocA reveals a pentameric aquaporin-like channel
Yi Wang1,4, Yongjian Huang2,4, Jiawei Wang2,4, Chao Cheng2, Weijiao Huang2, Peilong Lu1, Ya-Nan Xu3, Pengye Wang3, Nieng Yan2 & Yigong Shi1
1 Ministry of Education Protein Science Laboratory,
2 State Key Laboratory of Biomembrane and Membrane Biotechnology, Center for Structural Biology, School of Life Sciences and School of Medicine, Tsinghua University, Beijing 100084, China
3 Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
4 These authors contributed equally to this work.
Correspondence to: Nieng Yan2Yigong Shi1 Correspondence and requests for materials should be addressed to N.Y. or Y.S.
FocA is a representative member of the formate–nitrite transporter family, which transports short-chain acids in bacteria, archaea, fungi, algae and parasites. The structure and transport mechanism of the formate–nitrite transporter family remain unknown. Here we report the crystal structure of Escherichia coli FocA at 2.25 ? resolution. FocA forms a symmetric pentamer, with each protomer consisting of six transmembrane segments. Despite a lack of sequence homology, the overall structure of the FocA protomer closely resembles that of aquaporin and strongly argues that FocA is a channel, rather than a transporter. Structural analysis identifies potentially important channel residues, defines the channel path and reveals two constriction sites. Unlike aquaporin, FocA is impermeable to water but allows the passage of formate. A structural and biochemical investigation provides mechanistic insights into the channel activity of FocA.
