Myosin XXI is a motor found in the disease-causing organism Leishmania. Genome analysis identified only two myosin genes, a class IB and a class XXI. While no expression of myosin IB has been found in the organism to date, myosin XXI has been detected in both the promastigote and the amastigote stages of the Leishmania life cycle, where it is preferentially localised to the proximal region of the flagellum. The presence of only a single myosin isoform suggests that this myosin carries out a variety of functions within the protozoa, including possible roles in membrane anchorage as well as longer range directed movements with cargo. We have co-expressed myosin-XXI and calmodulin in a baculovirus system, and found that it binds a single calmodulin at its neck domain which is required for motility, although not for ATPase activity. Myosin XXI transports actin filaments in motility assays, and is insensitive to both high salt and Ca2+ concentrations up to pCa 4. Sequence analysis of myosin XXI identifies a leucine zipper as well as two short coiled-coil regions, suggesting that myosin XXI is able to dimerise. To confirm this hypothesis we expressed a variety of tail constructs and studied formation of dimerisation using gel filtration. We found that the tail fragment binds calmodulin and dimerises. Intriguingly the full-length myosin XXI initially appeared to be a monomer. Further studies showed the tails dimerise in a temperature dependent manner. While the tails are stable monomers below 20 oC, they form dimers above this. When this was repeated with the full-length protein we also observed the creation of dimers or higher state oligomers. We are further characterising this observation using electron microscopy and TIRF microscopy photobleaching experiments.Sponsored by DFG and Friedrich-Baur-Stiftung