Expression and purification of the membrane protein p7 from hepatitis C virus.

A small 63-residue membrane protein, p7, has essential roles in the infectivity of the hepatitis C virus in humans. This hydrophobic membrane protein forms homo-oligomeric ion channels in bilayers, which can be blocked by known channel-blocking compounds. To perform structural studies of p7 by nuclear magnetic resonance (NMR) spectroscopy, it is necessary to produce milligram quantities of isotopically labeled protein; as is the case for most membrane-associated proteins, this is challenging. We describe the successful expression of full-length p7 and two truncated constructs in Escherichia coli using a fusion partner that directs the overexpressed protein to inclusion bodies. Following isolation of the fusion proteins by affinity chromatography, they were chemically cleaved with cyanogen bromide. The p7-polypeptides were purified by size-exclusion chromatography. Solution NMR two-dimensional heteronuclear single quantum coherence spectra of uniformly (15) N-labeled p7-polypeptides in 1,2-dihexyl-1-sn-glycero-3-phosphocholine isotropic micelles are fully resolved, with a single resonance for each amide site. The solid-state NMR spectra of the same polypeptides in magnetically aligned 14-O-PC/6-O-PC bicelles demonstrate their reconstitution into planar phospholipid bilayers.