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是一种广泛存在但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，用于移动氨基酸、多胺和各种有机阳离子穿过细胞膜，具有多种生理目的。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，我们对其底物运输的基本机制的了解目前还很浅。细菌APC蛋白AdiC将精氨酸转移到许多肠道细菌中，是“极端耐酸”反应的关键角色，这些生物利用这种反应在胃的酸性环境中生存。这种特殊的APC蛋白可以在人工膜中过表达、纯化、功能重构，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是如何特异性识别其有机底物的，以及它是如何在生物膜上移动的。

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.