Recombinant tobacco mosaic virus movement protein is an RNA-binding, alpha-helical membrane protein

The 30-kDa movement protein (MP) is essential for cell-cell spread of tobac co mosaic Virus in planta. To explore the structural properties of MP, the full-length recombinant MP gene was expressed in Escherichia coil, and one- step purification from solubilized inclusion bodies was accomplished by usi ng anion exchange chromatography. Soluble MP was maintained at >4 mg/ml wit hout aggregation and displayed approximate to 70% alpha-helical conformatio n in the presence of urea and sos. A trypsin-resistant core domain of the M P had tightly folded tertiary structure, whereas 18 aa at the C terminus of the monomer were rapidly removed by trypsin. Two hydrophobic regions withi n the core were highly resistant to proteolysis. Based on results of CD spe ctroscopy, trypsin treatment, and MS, we propose a topological model in whi ch MP has two putative alpha-helical transmembrane domains and a protease-s ensitive carboxyl terminus.