Molecular characterization of myosin IB from the lower eukaryote Entamoeba histolytica, a human parasite1Note: The nucleotide sequence data reported in this paper have been submitted to the GenBank Data Library with the accession number U89655.1

Abstract

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 characteristic 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.