ENTAMOEBA-HISTOLYTICA AND ENTAMOEBA DISPAR - DIFFERENCES IN NUMBERS AND EXPRESSION OF CYSTEINE PROTEINASE GENES

In order to identify molecules that might be responsible for the diffe rence in pathogenicity between the two closely related protozoan paras ites Entamoeba histolytica and Entamoeba dispar, we focussed on cystei ne proteinases because this class of enzymes has been considered impor tant for pathogenic tissue destruction. By screening a genomic library derived from an E. histolytica isolate, a total of six distinct genes (ehcp1-ehcp6) encoding typical prepro-forms of cysteine proteinases w ere identified which differed from each other by 40% to 85% of their n ucleotide sequences. Three of these genes, ehcp1, ehcp2, and ehcp5, wh ich exhibited high levels of expression, were found to be responsible for approximately 90% of cysteine proteinase transcripts, whereas the remaining three were either not or only marginally expressed. Expressi on of the different genes directly correlated with the level of activi ty of the respective enzymes in trophozoite lysates. Purification of t he enzymes and N-terminal sequencing revealed that virtually all cyste ine proteinase activity of E. histolytica can be attributed to three e nzymes namely EhCP1, EhCP2 and EhCP5. Southern blot analysis indicated that just two of these abundantly expressed genes are missing in E. d ispar. On the other hand, genes analogous to four of the six genes ide ntified in E. histolytica were found to be present in E. dispar, but o nly two of these are expressed within the trophozoite stage.