BETA-AMINO-THIOLS INHIBIT THE ZINC METALLOPEPTIDASE ACTIVITY OF TETANUS TOXIN LIGHT-CHAIN

Tetanus neurotoxin is a 150-kDa protein produced by Clostridium tetani , which causes the lethal spastic paralytic syndromes of tetanus by bl ocking inhibitory neurotransmitter release at central synapses. The to xin light chain (50 kDa) has a zinc endopeptidase activity specific fo r synaptobrevin, an essential component of the neuroexocytosis apparat us. Previous unsuccessful attempts to block the proteolytic activity o f this neurotoxin with well-known inhibitors of other zinc proteases l ed us to study the design of specific inhibitors as a possible drug th erapy to prevent the progressive evolution of tetanus following infect ion. Starting from the synaptobrevin sequence at the level of the clea vage site by tetanus neurotoxin (Gln(76)-Phe(77)), a thiol analogue of glutamine demonstrated inhibitory activities in the millimolar range. A structure-activity relationship performed with this compound led us to determine the requirement for the correct positioning of the thiol group, the primary amino group, and a carboxamide or sulfonamide grou p on the side chain. This resulted in the design of a beta-amino-(4-su lfamoylphenyl)glycine-thiol, the first significantly efficient inhibit or of tetanus neurotoxin with a K-i value of 35 +/- 5 mu M.