1月20日，清華大學生命科學學院施一公教授領導的研究組在《自然》在線發(fā)表論文,，闡述在毒性大腸桿菌腸胃耐酸性保護機制中起重要作用的AdiC轉運蛋白的底物識別和轉運機理。這是繼他們在2009年于《科學》發(fā)表首個APC家族轉運蛋白晶體結構之后針對AdiC研究的又一重要突破,。
AdiC是逆向轉運arginine及其脫羧產物agmatine的轉運蛋白,。2009年5月,，施一公教授的研究組發(fā)表了AdiC在沒有底物狀況下的3.6埃的分子結構,，揭示了AdiC以二聚體形式存在,，同時還發(fā)現(xiàn)APC家族的轉運蛋白與其他幾類沒有序列同源性的鈉離子依賴性轉運蛋白具有相似的結構骨架。根據(jù)生化實驗結果,，他們推測出在轉運過程中起重要作用的氨基酸殘基以及可能的轉運模型,。
在《自然》最新發(fā)表的論文中，施一公研究組解析了AdiC在arginine結合狀態(tài)下的3.0埃的晶體結構,。這個較高分辨率的結構顯示,，過去報道的AdiC由于分辨率偏低、數(shù)據(jù)質量有限,，因而盡管基本結論正確,，但在部分跨膜螺旋區(qū)域，施一公的研究組以及美國另一研究組均存在結構修正不妥之處,。所以在這一篇文章里，他們首先糾正了兩個組以前的偏差,，然后比較了AdiC在沒有底物和結合arginine的狀態(tài)下的結構,。這一比較顯示，在結合arginine時,，AdiC的跨膜螺旋TM6旋轉了近40°,，覆蓋于底物之上,，使底物處于一個完全封閉的表面呈負電勢的腔中。在這一觀測的基礎上,，結合以往的生化數(shù)據(jù),，他們進一步修正了AdiC的轉運模型，提出了逆向轉運蛋白雙結合位點的模型,。（生物谷Bioon.com）
施一公近期科研成果：
PNAS：膜蛋白酶S2P活性調控研究
NSMB：解析TIPE2晶體結構
Cell：PSPs的結構以及生化功能
Molecular Cell：PP2A調節(jié)Tau蛋白脫磷酸
傳說人物施一公——生物谷盤點2009
生物谷推薦原始出處：
Nature advance online publication 20 January 2010 | doi:10.1038/nature08741
Mechanism of substrate recognition and transport by an amino acid antiporter
Xiang Gao1,4, Lijun Zhou2,4, Xuyao Jiao2,3, Feiran Lu2, Chuangye Yan2, Xin Zeng1, Jiawei Wang2 & 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 School of Life Sciences, Shandong University, Jinan, Shandong 250100, China
4 These authors contributed equally to this work.
5 Correspondence to: Yigong Shi1 Correspondence and requests for materials should be addressed to Y.S.
In extremely acidic environments, enteric bacteria such as Escherichia coli rely on the amino acid antiporter AdiC to expel protons by exchanging intracellular agmatine (Agm2+) for extracellular arginine (Arg+)1, 2, 3. AdiC is a representative member of the amino acid-polyamine-organocation (APC) superfamily of membrane transporters4, 5. The structure of substrate-free AdiC revealed a homodimeric assembly, with each protomer containing 12 transmembrane segments and existing in an outward-open conformation6, 7. The overall folding of AdiC is similar to that of the Na+-coupled symporters8, 9, 10, 11. Despite these advances, it remains unclear how the substrate (arginine or agmatine) is recognized and transported by AdiC. Here we report the crystal structure of an E. coli AdiC variant bound to Arg at 3.0?? resolution. The positively charged Arg is enclosed in an acidic binding chamber, with the head groups of Arg hydrogen-bonded to main chain atoms of AdiC and the aliphatic portion of Arg stacked by hydrophobic side chains of highly conserved residues. Arg binding induces pronounced structural rearrangement in transmembrane helix 6 (TM6) and, to a lesser extent, TM2 and TM10, resulting in an occluded conformation. Structural analysis identified three potential gates, involving four aromatic residues and Glu?208, which may work in concert to differentially regulate the upload and release of Arg and Agm.
