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Molecular motors

The mitotic spindle is just one part of the wider cytoskeleton – the system of filaments and motors that is crucial for cell shape, division, movement and growth in all eukaryotic cells. Trypanosomes rely heavily on the tubulin-based cytoskeleton for many cellular functions, with less dependence on actin filaments than is the case for animals. In fact, actin appears to be dispensable for at least some of the parasite's lifecycle. Trypanosomes also have an unusual complement of cytoskeleton motors, many of which are of unknown function (see here).

kinesin families
Distribution of families of kinesins in eukaryotes. Presence of family in a genome is indicated by a filled circle, absence/not-found is indicated by an open circle. Extract from a larger figure in Wickstead et al. (2010) BMC Evol Biol 10:110.

There are three major classes of motor protein that move on the cytoskeleton of eukaryotes (that is, more complex non-bacterial organisms) – myosins, kinesins and dyneins. Only kinesins have thus-far been seen to be ubiquitously present in all eukaryotes, with losses of either all myosins or all dyneins from particular branches of the eukaryotic tree. All three motor classes are superfamilies of proteins encompassing multiple types with specific functions. The lab has worked extensively to characterize the types of motor found in cells and in this way has discovered "new" families of motors for which little functional data are available. Work in the lab is characterizing these families and also testing the function of unclassified motors in trypanosome growth and division.

kinesin tree
Extract of a comprehensive phylogenetic analysis of the kinesin protein superfamily. The tree represents a consensus of 8 Bayesian analyses of kinesins from 45 diverse eukaryotes. Two measures of topology support are shown (values >0.95 emboldened). Protein domain architecture have been mapped onto the tree. Based on the analysis in Wickstead et al. (2010) BMC Evol Biol 10:110.

The above tree is an extract from our latest analysis (Wickstead et al. (2010) BMC Evol Biol 10:110) of 1624 kinesin-like proteins from 45 diverse eukaryotes. The full tree with predicted protein architectures is available here either in PDF or PNG (bitmap) format. The PDF offers the ability to search the text for proteins of interest, but it is a large, complex document so it may slow/crash your machine! Classification of all 1624 kinesins is available as Supplemental data.

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