MOLECULAR CHARACTERIZATION OF MYOSIN IB FROM THE LOWER EUKARYOTE ENTAMOEBA-HISTOLYTICA, A HUMAN PARASITE

The complete amino acid sequence of the Entamoeba histolytica unconven tional myosin IB (Eh-myosin IB) is reported. Sequencing of overlapping cDNA fragments reveals a single open reading frame which predicts a 1 30 kDa protein of 1049 aa. Eh-myosin IB presents the three characteris tic domains of myosins I subclass 1. This protein presents homology wi th myosins IB from other amoebae, but striking homologies with vertebr ate unconventional myosins were also observed. The predicted actin and ATP-binding sites are located in the head domain. The heavy chain pho sphorylation region is homologous to metazoan myosins I with an acidic residue present at the phosphorylation site. In the neck domain, an I Q motif indicates potential binding of calmodulin to the myosin I heav y chain. In the tail of Eh-myosin IB the three characteristic regions of myosin I are found. A putative membrane binding domain, a very shor t domain rich in alanine and proline we demonstrate to be functional f or actin binding, and the src-homology 3 domain. The Entamoeba histoly tica myosin IB is the first unconventional myosin so far described in a lower eukaryote. (C) 1997 Elsevier Science B.V.