News from the Myosin Tree: 1000 New Sequences, 100 New Species, 1 New Class

Abstract

The myosins constitute one of the largest and most divergent protein families in eukaryotes. They are characterized by a motor domain that binds to actin in an ATP-dependent manner, a neck domain consisting of varying numbers of IQ motifs, and amino-terminal and carboxy-terminal domains of various length and function. Myosins are involved in many cellular tasks like organelle trafficking, cytokinesis, maintenance of cell shape, and muscle contraction. They are typically classified based on the phylogenetic analysis of the motor domain. In 2007, we have published the analysis of over 2200 myosins from more than 320 species that resulted in 35 myosin classes of which 16 had not been proposed before. Here, we present an update on the myosin tree that is now based on 3246 myosins from 422 species. All sequences were manually annotated and verified. Most of the newly sequenced species belong to taxa that have already been covered in the earlier analysis. However, 1 new class has been determined that is specific to metazoans. These class-36 myosins do not contain an N-terminal SH3-like domain and their tail consists of more than 10 transmembrane domains and a chitin synthase domain. In addition, the genome sequences of the amoeba Acanthamoeba castellanii and the coccolithophore Emiliana huxleyi revealed many new orphan myosins. All sequence related data is available via CyMoBase at www.cymobase.org.