期刊
NATURE
卷 497, 期 7451, 页码 647-+出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/nature12139
关键词
-
资金
- Office of Science, Office of Basic Energy Sciences, of the US Department of Energy [DE-AC02-05CH11231]
- Howard Hughes Medical Institute
Mineral nitrogen in nature is often found in the form of nitrate (NO3-). Numerous microorganisms evolved to assimilate nitrate and use it as a major source of mineral nitrogen uptake(1). Nitrate, which is central in nitrogen metabolism, is first reduced to nitrite (NO2-) through a two-electron reduction reaction(2,3). The accumulation of cellular nitrite can be harmful because nitrite can be reduced to the cytotoxic nitric oxide. Instead, nitrite is rapidly removed from the cell by channels and transporters, or reduced to ammonium or dinitrogen through the action of assimilatory enzymes(3). Despite decades of effort no structure is currently available for any nitrate transport protein and the mechanism by which nitrate is transported remains largely unknown. Here we report the structure of a bacterial nitrate/nitrite transport protein, NarK, from Escherichia coli, with and without substrate. The structures reveal a positively charged substrate-translocation pathway lacking protonatable residues, suggesting that NarK functions as a nitrate/nitrite exchanger and that protons are unlikely to be co-transported. Conserved arginine residues comprise the substrate-binding pocket, which is formed by association of helices from the two halves of NarK. Key residues that are important for substrate recognition and transport are identified and related to extensive mutagenesis and functional studies. We propose that NarK exchanges nitrate for nitrite by a rocker switch mechanism facilitated by inter-domain hydrogen bond networks.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据