SECONDARY STRUCTURAL PREDICTIONS FOR THE CLOSTRIDIAL NEUROTOXINS

The primary structures of a family of ten clostridial neurotoxins have recently been deduced yet little information is presently available c oncerning their secondary or tertiary structures, Because the overall similarity percentage of multiply aligned sequences is high, the secon dary structures of these metalloendopeptidases are also expected to be conserved. The neural net program, PHD (Rest and Sander, Proc. Natl. Acad, Sci, USA 90:7558-7562, 1993), predicted that the secondary struc tures of the neurotoxins were indeed conserved in both single and mult iple sequence modes of analysis, Predictions for the amounts of helica l, extended, and loop states from the single sequence analyses were co nsistent with previously published data from circular dichroism studie s on some of these neurotoxins. In the single analysis mode, only the aligned regions were predicted to show conservation of the three-state structure, In contrast, the multiple sequence analysis predicted that a conserved state (variable loops) also exists in non-aligned regions . Alignments with the primary structure of the prototypic metalloendop eptidase thermolysin showed that about 25% of-the residues within this enzyme are similar to those in the neurotoxins, A comparison of therm olysin's known secondary structure with the predictions from this stud y showed that about 80% of thermolysin's residues could be structurall y aligned with those in the neurotoxins, These predictions provide the necessary framework to build a homologous low-resolution tertiary str ucture of the neurotoxin active site that will be essential in the dev elopment of synthetic inhibitors. (C) 1994 Wiley-Liss, Inc.