She. Vandenworm et al., CRYSTAL-STRUCTURES OF MS2 COAT PROTEIN MUTANTS IN COMPLEX WITH WILD-TYPE RNA OPERATOR FRAGMENTS, Nucleic acids research, 26(5), 1998, pp. 1345-1351
In MS2 assembly of phage particles results from an interaction between
a coat protein dimer and a stem-loop of the RNA genome (the operator
hairpin), Amino acid residues Thr45, which is universally conserved am
ong the small RNA phages, and Thr59 are part of the specific RNA bindi
ng pocket and interact directly with the RNA; the former through a hyd
rogen bond, the latter through hydrophobic contacts, The crystal struc
tures of MS2 protein capsids formed by mutants Thr45Ala and Thr59Ser,
both with and without the 19 nt wild-type operator hairpin bound, are
reported here, The RNA hairpin binds to these mutants in a similar way
to its binding to wild-type protein. In a companion paper both mutant
s are shown to be deficient in RNA binding in an in vivo assay, but in
vitro the equilibrium dissociation constant is significantly higher t
han wild-type for the Thr45Ala mutant, The change in binding affinity
of the Thr45Ala mutant is probably a direct consequence of removal of
direct hydrogen bonds between the protein and the RNA, The properties
of the Thr59Ser mutant are more difficult to explain, but are consiste
nt with a loss of non-polar contact.