A redetermination of the structure of the triple mutant(K53,56,120M) of phospholipase A2 at 1.6 Å resolution using sulfur-SAS at 1.54 Å wavelength

The crystal structure of the triple mutant K53,56,120M of bovine pancreatic phospholipase A(2) has been redetermined using sulfur single-wavelength anomalous scattering. The synchrotron data-were collected at lambda = 1.54 Angstrom and the crystal diffracted to 1.6 Angstrom resolution. The program SOLVE was used to locate the heavy atoms and to estimate the initial phases and the resulting map was then subjected to RESOLVE. The output of 455 non-H atoms, including 12 S atoms, one calcium ion and one chloride ion, were then subjected toARP/wARP followed by REFMAC With the improved phases, the automaticmodel building successfully built more than 85%, of the 123 residues, excluding the N- and C-terminal residues. The final crystallographic R factor is 17.7% (R-free = 21.7%). The refined model consists of 954 non-H protein atoms, 165 water 0 atoms, three 2-methyl-2,4-pentanediol (MPD) molecules, one calcium ion and one chloride ion. The present work is yet another example that shows the utility of single-wavelength anomalous scattering data for solving a protein structure