Crystal structure of an N-terminal fragment SNR141 of Staphylococcal nuclease R refined at 1.9 angstrom resolution

Staphylococcul nuclease R (SNaseR) is an analogue of Staphylococcal nucleas e (SNaseA). SNR141 is one of the N-terminal fragments of SNaseR, which has been highly expressed in and purified from E. coli and used to study nascen t peptide folding. Single crystals of SNR141 suitable for X-ray analysis we re grown in space group P4, with unit cell of a = b = 48.2 Angstrom and c = 63.8 Angstrom by hanging drops vapour diffusion. Through the difference Fo urier technique and restrained least square method, the crystal structure o f SNR141 her been determined to 1.9 Angstrom resolution with a final R fact or of 0.198. The r.m.s. deviations in the bond lengths and in the bond ange ls are 0.016 Angstrom and 3.3 degrees, respectively. The results of the cry stal structure indicated that the deletion of 8 amino-acid residues from th e C-terminal end of SNaseR perturbs the conformation of residue Tyr113 and blocks the binding between enzyme and substrate, which causes the biologica l activity of SNR141 down to 80% of wild type nuclease.