所有活細(xì)胞都積累鉀離子,，而很高的細(xì)胞內(nèi)鉀濃度是很多生理過程所必需的,。在細(xì)菌、酵母和植物中,，鉀離子吸收是由一個超級家族的運(yùn)輸?shù)鞍?ldquo;SKT蛋白”實現(xiàn)的,。這些蛋白被認(rèn)為是從簡單的鉀通道形成的，但是鉀離子選擇性和運(yùn)輸?shù)臋C(jī)制卻不清楚?，F(xiàn)在,，一種細(xì)菌SKT蛋白（來自“副溶血性弧菌”的TrkH鉀運(yùn)輸?shù)鞍祝┑木w結(jié)構(gòu)已被確定。它的選擇性過濾器與鉀離子通道中的擇性過濾器相似,，但較短,。生物化學(xué)研究表明，K+選擇性取決于一個新的門控機(jī)制,，該機(jī)制將Na+和Li+等較小的離子排除在外,，而讓K+和Rb+等較大的離子進(jìn)來。（生物谷Bioon.com）
生物谷推薦原文出處：
Nature doi:10.1038/nature09731
Crystal structure of a potassium ion transporter, TrkH
Yu Cao,1, 11 Xiangshu Jin,2, 11 Hua Huang,1, 11 Mehabaw Getahun Derebe,3 Elena J. Levin,1 Venkataraman Kabaleeswaran,1 Yaping Pan,1 Marco Punta,4, 5 James Love,4 Jun Weng,1 Matthias Quick,6, 7 Sheng Ye,3 Brian Kloss,4 Renato Bruni,4 Erik Martinez-Hackert,8 Wayne A. Hendrickson,8 Burkhard Rost,4, 5 Jonathan A. Javitch,6, 7, 9 Kanagalaghatta R. Rajashankar,10 Youxing Jiang3 & Ming Zhou1
The TrkH/TrkG/KtrB proteins mediate K+ uptake in bacteria and probably evolved from simple K+ channels by multiple gene duplications or fusions. Here we present the crystal structure of a TrkH from Vibrio parahaemolyticus. TrkH is a homodimer, and each protomer contains an ion permeation pathway. A selectivity filter, similar in architecture to those of K+ channels but significantly shorter, is lined by backbone and side-chain oxygen atoms. Functional studies showed that TrkH is selective for permeation of K+ and Rb+ over smaller ions such as Na+ or Li+. Immediately intracellular to the selectivity filter are an intramembrane loop and an arginine residue, both highly conserved, which constrict the permeation pathway. Substituting the arginine with an alanine significantly increases the rate of K+ flux. These results reveal the molecular basis of K+ selectivity and suggest a novel gating mechanism for this large and important family of membrane transport proteins.
