施一公教授的研究組近年來一直致力于病原微生物及癌細(xì)胞抗酸系統(tǒng)膜轉(zhuǎn)運(yùn)蛋白的研究，發(fā)表了一系列高影響力的科學(xué)論文。在09年至12年，分別報(bào)道了從屬于抗酸系統(tǒng)3的膜轉(zhuǎn)運(yùn)蛋白AdiC和從屬于抗酸系統(tǒng)2的膜轉(zhuǎn)運(yùn)蛋白GadC的處于三種不同狀態(tài)的晶體結(jié)構(gòu)【Gao et al, 2009, science; Gao et al, 2010, Nature; Ma et al, 2012, Nature】，并通過生化手段揭示了抗酸過程中底物跨膜運(yùn)輸?shù)姆肿訖C(jī)理，提出了一個(gè)由谷氨酰胺參與的全新抗酸系統(tǒng)模型【Lu et al, 2013, Cell Research; Ma et al, 2013, JBC】;在此研究的基礎(chǔ)上他們還開展了針對(duì)癌細(xì)胞抗酸機(jī)制的研究【Huang et al, 2013, Cell Research】。
原文摘要：
Molecular mechanism of pH-dependent substrate transport by an arginine-agmatineantiporter
Sheng Wang, Renhong Yan, Xi Zhang, Qi Chu, and Yigong Shi
Enteropathogenic bacteria, exemplified by Escherichia coli, rely on acid-resistance systems (ARs) to survive the acidic environment of the stomach. AR3 consumes intracellular protons through decarboxylation of arginine (Arg) in the cytoplasm and exchange of the reaction product agmatine (Agm) with extracellular Arg. The latter process is mediated bythe Arg:Agm antiporter AdiC, which is activated in response to acidic pH and remains fully active at pH 6.0 and below. Despite our knowledge of structural information, the molecularmechanism by which AdiC senses acidic pH remains completely unknown. Relying on alanine-scanning mutagenesisand an in vitro proteoliposome-based transport assay, we have identified Tyr74 as a critical pH sensor in AdiC. The AdiC variant Y74A exhibited robust transport activity at all pH values examined while maintaining stringent substratespecificity for Arg:Agm. Replacement of Tyr74 by Phe, but notby any other amino acid, led to the maintenance of pH-dependent substrate transport. These observations, in conjunction with structural information, identify a working model for pH-induced activation of AdiC in which a closed conformation is disrupted by cation–π interactions between proton and the aromatic side chain of Tyr74.
