Structure and Mechanism of a Virtual Proton Pump

描述（由申请人提供）：本提案的目的是确定AdiC的结构，AdiC是一类广泛存在且鲜为人知的膜转运蛋白-APC超家族的成员。APC蛋白在生物界几乎无处不在，用于将氨基酸、多胺和各种有机阳离子跨细胞膜移动，用于多种生理目的。虽然这是一个巨大的分子超家族，但没有任何APC蛋白的高分辨率结构是已知的，并且我们对它们的底物转运的基本机制的理解目前是肤浅的。细菌APC蛋白AdiC将精氨酸转移到许多肠道细菌中，是这些生物体用于在暴露于胃的酸性环境中生存的"极端耐酸性"反应的关键参与者。这种特殊的APC蛋白可以过表达，纯化，在人工膜中功能性重建，最重要的是，结晶。该项目旨在通过X射线晶体学确定AdiC的结构，并利用这些结构信息来了解这种蛋白质如何特异性地识别其有机阳离子底物以及它如何穿过生物膜。 公共卫生相关性：该项目在两个方面与人类健康相关。首先，通过提供关于一类新的膜蛋白分子工作机制的基本信息，它将阐明细胞用必需氨基酸营养素滋养自己的方式。其次，这种特殊的蛋白质家族不仅与健康中的基本人类生理学密切相关，而且还与破坏性病理学密切相关，特别是需要APC转运蛋白为快速生长的恶性细胞提供氨基酸的各种癌症。

DESCRIPTION (provided by applicant): The aim of this proposal is to determine the structure of AdiC, a member of a widespread and little-understood class of membrane transport proteins - the APC superfamily. APC proteins, nearly ubiquitous in the biological world, are used to move amino acids, polyamines, and a variey of organic cations across cell membranes for a multitude of physiological purposes. Although this is a huge molecular superfamily, no high-resolution structures are known for any APC proteins, and our understanding of their fundamental mechanisms of substrate transport is currently shallow. The bacterial APC protein AdiC, which moves arginine into many enteric bacteria, is a key player in the "extreme acid resistance" response that these organisms use to survive exposure to the acid environment of the stomach. This particular APC protein may be overexpressed, purified, functionally reconstituted in artificial membranes, and, most importantly, crystallized. The project aims to determine the structure of AdiC by x-ray crystallography, and to use this structural information to understand how this protein specifically recognizes its organocationic substrates and how it moves threse across the biological membrane. PUBLIC HEALTH RELEVANCE: This project is relevant to human health in two ways. First, by providing fundamental information on the edge of discovery about the molecular workings of a new class of membrane protein, it will illuminate the ways that cells nourish themselves with essential amino acid nutrients. Second, this particular protein family is intimately involved not only in essential human physiologies in health, but also in devastating pathologies, in particular a variety of cancers that require APC transporters to supply amino acids to fast-growing, malignant cells.