Characterization of the trypsin-like activity of Bacteroides forsythus

Abstract

Bacteroides forsythus, a bacterial species frequently associated with diseased periodontal sites, is known to possess trypsin-like activity. The present study was undertaken to determine the major characteristics of this activity. The trypsin-like activity was mainly found on the surface of the bacteria and could be solubilized with a zwitterionic detergent (Zwittergent 3-14). Using N-α-benzoyl-DL-arginine-p-nitroanilide as substrate, the optimum pH was between 7.5 and 8.5 and the optimum temperature was 35°C. The evidence suggests that the enzyme is a serine protease since it was strongly inhibited by diisopropylfluorophosphate (DFP), N-α-p-tosyl-L-lysine chloromethyl ketone hydrochloride, leupeptin and antipain. The B. forsythus trypsin-like enzyme cleaved numerous chromogenic synthetic peptides containing either an arginine or lysine bond, but could not hydrolyse native proteins including casein, gelatin and BSA. Incubation of a cell envelope extract of B. forsythus in the presence of [3H]DFP, which is known to bind irreversibly to serine proteases, labelled two bands at 70 and 81 kDa following SDS-PAGE (under reducing conditions) and fluorography. It is suggested that the B. forsythus trypsin-like enzyme may be mainly involved in the degradation of small peptides resulting from hydrolysis of larger proteins by other oral bacteria.