The NMR structure of the severe acute respiratory syndrome coronavirus
nonstructural protein (nsp) 7 in aqueous solution at pH 6.5 was determined and
compared with the results of previous structure determinations of nsp7 in
solution at pH 7.5 and in the crystals of a hexadecameric nsp7/nsp8 complex
obtained from a solution at pH 7.5. 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 pH 6.5, which provide
further insights into the polymorphisms implicated by a comparison of the three
presently available nsp7 structures.
