Identification and gene expression analysis of a large family of transmembrane kinases related to the Gal/GalNAc lectin in Entamoeba histolytica

We identified in the Entamoeba histolytica genome a family of over 80 putative transmembrane kinases (TMKs). The TNIK extracellular domains had significant similarity to the intermediate subunit (Igl) of the parasite GaI/GaINAc lectin. The closest homolog to the E. histolytica TMK kinase domain was a cytoplasmic dual-specificity kinase, SplA, from Dictyostelium discoideum. Sequence analysis of the TMK family demonstrated similarities to both serine/threonine and tyrosine kinases. TNIK genes from each of six phylogenetic groups were expressed as mRNA in trophozoites, as assessed by spotted oligoarray and real-time PCR assays, suggesting nonredundant functions of the TMK groups for sensing and responding to extracellular stimuli. Additionally, we observed changes in the expression profile of the TMKs in continuous culture. Antisera produced against the conserved kinase domain identified proteins of the expected molecular masses of the expressed TMKs. Confocal microscopy with anti-TMK kinase antibodies revealed a focal distribution of the TMKs on the cytoplasmic face of the trophozoite plasma membrane. We conclude that E. histolytica expresses members of each subgroup of TMKs. The presence of multiple receptor kinases in the plasma membrane offers for the first time a potential explanation of the ability of the parasite to respond to the changing environment of the host.