Molecular characterization of myosin IB from the lower eukaryote Entamoeba histolytica, a human parasite.

The complete amino acid sequence of the Entamoeba histolytica unconventional myosin IB (Eh-myosin IB) is reported. Sequencing of overlapping cDNA fragments reveals a single open reading frame which predicts a 130 kDa protein of 1049 aa. Eh-myosin IB presents the three characteristics domains of myosins I subclass 1. This protein presents homology with myosins IB from other amoebae, but striking homologies with vertebrate unconventional myosins were also observed. The predicted actin and ATP-binding sites are located in the head domain. The heavy chain phosphorylation region is homologous to metazoan myosins I with an acidic residue present at the phosphorylation site. In the neck domain, an IQ motif indicates potential binding of calmodulin to the myosin I heavy chain. In the tail of Eh-myosin IB the three characteristic regions of myosin I are found. A putative membrane binding domain a very short domain rich in alanine and proline we demonstrate to be functional for actin binding, and the src-homology 3 domain. The Entamoeba histolytica myosin IB is the first unconventional myosin so far described in a lower eukaryote.