PDBsum entry 3hqk

Transport protein

PDB id: 3hqk

Contents

Protein chains

418 a.a.

218 a.a.

211 a.a.

References listed in PDB file

Key reference

• Title: Structure of a prokaryotic virtual proton pump at 3.2 a resolution.
• Authors: Y.Fang, H.Jayaram, T.Shane, L.Kolmakova-Partensky, F.Wu, C.Williams, Y.Xiong, C.Miller.
• Ref.: Nature, 2009, 460, 1040-1043.
• PubMed id: 19578361

Abstract

To reach the mammalian gut, enteric bacteria must pass through the stomach. Many such organisms survive exposure to the harsh gastric environment (pH 1.5-4) by mounting extreme acid-resistance responses, one of which, the arginine-dependent system of Escherichia coli, has been studied at levels of cellular physiology, molecular genetics and protein biochemistry. This multiprotein system keeps the cytoplasm above pH 5 during acid challenge by continually pumping protons out of the cell using the free energy of arginine decarboxylation. At the heart of the process is a 'virtual proton pump' in the inner membrane, called AdiC, that imports L-arginine from the gastric juice and exports its decarboxylation product agmatine. AdiC belongs to the APC superfamily of membrane proteins, which transports amino acids, polyamines and organic cations in a multitude of biological roles, including delivery of arginine for nitric oxide synthesis, facilitation of insulin release from pancreatic beta-cells, and, when inappropriately overexpressed, provisioning of certain fast-growing neoplastic cells with amino acids. High-resolution structures and detailed transport mechanisms of APC transporters are currently unknown. Here we describe a crystal structure of AdiC at 3.2 A resolution. The protein is captured in an outward-open, substrate-free conformation with transmembrane architecture remarkably similar to that seen in four other families of apparently unrelated transport proteins.