THE 3-DIMENSIONAL STRUCTURE OF NOTEXIN, A PRESYNAPTIC NEUROTOXIC PHOSPHOLIPASE-A(2) AT 2.0 ANGSTROM RESOLUTION

The three-dimensional structure of notexin has been solved by molecular replacement methods. The structure has been refined at 2.0 angstrom resolution to a crystallographic R-value of 16.5% with good stero-chemistry. The core of the protein is very similar to other phospholipase A2s (PLA2s) but several parts of the molecule are distinctly different. The most significant differences from PLA2s from bovine pancreas and rattlesnake occur in the stretches 56-80 and 85-89. Residue 69, which has been showed to be important for phospholipase binding, has a different conformation and different interactions than in other known PLA2s. The C-alpha positions for residues 86-88 differ by about 6 angstrom from both the bovine and the rattlesnake enzyme. The crystals contain no Ca2+. Instead, a water molecule occupies the calcium site.