X-ray crystallographic studies of two nucleic -acid binding protein/complex systems and one collagen -like peptide

The structures of two nucleic-acid binding protein/complex systems and one collagen-like peptide have been determined by x-ray crystallographic methods. These include influenza virus ns1 protein and its complex with RNA, a ternary complex of catabolite activator protein (CAP), DNA and the C-terminal domain of the alpha subunit of RNA polymerase (RNAP alpha-CTD) from escherichia coli, and a collagen-like peptide with the discontinuity in the middle of the collagen helical region.;The crystal structure of the N-terminal RNA binding domain of influenza virus NS1 (Non Structural protein 1) protein has been determined at 1.9 A resolution (Liu et al., 1997). NS1 protein binds to several kinds of RNA including poly (A), U6 snRNA, and dsRNA. The structure shows a dimer of the RNA-binding domain, which forms a unique six-helical topology for an RNA-binding protein. The monomer structure shows some similarity with the other DNA/RNA-binding proteins, which could suggest the possible mode it binds to the RNA targets. The structural study of the complex of NS1/RNA is in progress.;A ternary structure from E. coli has been solved at 2.9 A containing the C-terminal domain of the alpha subunit of RNA polymerase from E. coli (alpha-CTD), the Catabolite gene Activator Protein (CAP), and a 40 base pair DNA duplex. The alpha-CTD forms a dimer through a crystallographic two-fold with a surface for alpha-CTD, DNA and CAP binding now seen buried in the dimer interface. The X-ray crystal structure as well as biochemical data indicates a possible switching mechanism where the dimerization of alpha-CTD represents the inactive form in contrast to the active form when the dimer releases.;The structure of a collagen-like peptide, (Pro-Hyp-Gly)4-Pro-Gly-(Pro-Hyp-Gly) 5 or Hyp-, has been determined to 2.0 A resolution. This peptide was designed to model one of the common discontinuities in the collagen molecules as well as in other triple-helical motif. The Hyp- structure displays an overall 7-fold symmetry and a local unwinding in the discontinuity site. The angular registry of the helix is maintained through the whole structure due to the different compensation effect from interruption of the individual chain.