EF-hand proteins in onychophorans as compared to tardigrades and other ecdysozoans

To learn more about the regulation of muscle contraction in the structural and functionally different muscles in Ecdysozoa, we have analysed the four EF-hand proteins calmodulin (CaM), troponin C (TnC), essential myosin light chain (eMLC) and regulatory myosin light chain (rMLC) in the velvet worm Peripatoides sp. These proteins are typified by a helix-loop-helix motif and trigger the actin–myosin interaction in muscle tissue and non-muscle cells by coordinative binding of calcium ions. CaM (632 bp) and TnC (853 bp) revealed 4 and 2 potential calcium-binding domains, respectively. Based on analysis of both MLCs, only the rMLC (798 bp) showed one potential N-terminal EF-hand domain and a consensus phosphorylation sequence motif, which suggests a phosphorylation of this myosin light chain. We have compared these results with previously published data from the eutardigrade Hypsibius klebelsbergi and found striking conformity between both taxa. Further, we compared the new sequences with corresponding sequences from nematodes and arthropods retrieved from GenBank.