ISOLATION AND MOLECULAR CHARACTERIZATION OF A SURFACE-BOUND PROTEINASE OF ENTAMOEBA-HISTOLYTICA

Major pathogenic functions of Entamoeba histolytica involved in destru ction of host tissues are the degradation of extracellular matrix prot eins mediated by secreted cysteine proteinases and contact-dependent k illing of host cells via membrane-active factors. A soluble protein wi th an affinity for membranes was purified from amoebic extracts to app arent homogeneity. N-terminal sequencing and subsequent molecular clon ing of the factor revealed that it is a member of the cysteine protein ase family of E. histolytica, which we termed CP5. Further experiments with the purified protein showed that it has potent proteolytic activ ity that is abrogated in the presence of inhibitors specific for cyste ine proteinases. The enzyme firmly associates with membranes retaining its proteolytic activity and it produces cytopathic effects on cultur ed monolayers. A model of the three-dimensional structure of CP5 revea led the presence of a hydrophobic patch that may account for the poten tial of the protein to associate with membranes. Immunocytochemical lo calization of the enzyme to the surface of the amoeba in combination w ith the recent finding that the gene encoding CP5 is missing in the cl osely related but non-pathogenic Entamoeba dispar suggests a potential role of the protein in host tissue destruction of E. histolytica.