REFINED X-RAY CRYSTALLOGRAPHIC STRUCTURE OF THE POLIOVIRUS 3C GENE-PRODUCT

The X-ray crystallographic structure of the recombinant poliovirus 3C gene product Mahoney strain) has been determined by single isomorphous replacement and non-crystallographic symmetry averaging and refined a t 2.1 Angstrom resolution. Poliovirus 3C is comprised of two six-stran ded antiparallel beta-barrel domains and is structurally similar to th e chymotrypsin-like serine proteinases. The shallow active site cleft is located at the junction of the two beta-barrel domains and contains a His40, Glu71, Cys147 catalytic triad. The polypeptide loop precedin g Cys147 is flexible and Likely undergoes a conformational change upon substrate binding. The specificity pockets for poliovirus 3C are well -defined and modeling studies account for the known substrate specific ity of this proteinase. Poliovirus 3C also participates in the formati on of the viral replicative initiation complex where it specifically r ecognizes and binds the RNA stem-loop structure in the 5' non-translat ed region of its own genome. The RNA recognition site of 3C is located on the opposite side of the molecule in relation to its proteolytic a ctive site and is centered about the conserved KFRDIR sequence of the domain Linker. The recognition site is well-defined and also includes residues from the amino and carboxy-terminal helices. The two molecule s in the asymmetric unit are related by an approximate 2-fold, non-cry stallographic symmetry and form an intermolecular antiparallel beta-sh eet at their interface. (C) 1997 Academic Press Limited.