Discussion

The kinesin and kinesin-like protein superfamily is among one of the largest in Trypanosoma brucei, with almost 100 encoding genes dispersed throughout the genome. Among these is a gene encoding a protein we call TbPH1 (Tb927.3.2490), which contains a pleckstrin homology (PH) domain that inspired its name. The 110 kDa multidomain protein is made up of an N-terminal kinesin domain whose Walker A motif is ablated by a single substitution, an intervening coiled-coil region, followed by the PH and helix-turn-helix domains. While its role as a microtubule motor is suspect, it bears other motifs that suggest interactions with other proteins, lipids and even double-stranded nucleic acids. RNAi-silencing of TbPH1 in procyclic (PCF) and long slender bloodstream (BSF) forms compromises parasite fitness, likely due to a cell cycle defect resulting in an accumulation of 1N2K cells. In situ N- and C-terminal epitope-tagging reveals an interesting, somewhat punctate localization pattern that is distributed throughout the cell but often enriched between the nucleus and kinetoplast. Its localization predominantly excludes such organelles as the mitochondrion, endoplasmic reticulum and acidocalcisomes. Fractionation of T. brucei into cytoskeleton and soluble fractions does not support TbPH1 being a component of the former. However, TbPH1 is trapped by microtubule sieving and released when the corset is depolymerized in high salt conditions.