Oligosaccharyltransferase COST) is a membrane associated enzyme complex that mediates transfer of an oligosaccharide onto asparagine residue of a protein. Human Ost4 is a small membrane protein and belongs to one of the seven subunits of human OST. This study determined the solution structure of human Ost4 in solvent system using NMR spectroscopy. Ost4 was demonstrated that the residues 5-30 adopt an alpha-helical structure. A kink structure was observed in the transmembrane domain, which may be important for its function. (C) 2011 Elsevier Inc. All rights reserved.