NMR Structure of the SARS-CoV Nonstructural Protein 7 in Solution at pH6.5

The NMR structure of the severe acute respiratory syndrome coronavirus nonstructural protein (nsp) 7 in aqueous solution at pH6.5 was determined and compared with the results of previous structure determinations of nsp7 in solution at pH7.5 and in the crystals of a hexadecameric nsp7/nsp8 complex obtained from a solution at pH7.5. All three structures contain four helices as the only regular secondary structures, but there are differences in the lengths and sequence locations of the four helices, as well as between the tertiary folds. The present study includes data on conformational equilibria and intramolecular rate processes in nsp7 in solution at pH6.5, which provide further insights into the polymorphisms implicated by a comparison of the three presently available nsp7 structures.