4 years ago

Binding Of A Newly Identified Essential Light Chain To Expressed Plasmodium falciparum Class XIV Myosin Enhances Actin Motility

Previs, Trybus, C. S., R., Bookwalter, Fagnant, K. M., C. L., Krementsova, Baum, J., McCrorie, M. J., Tay, E. B., P. M.
Motility of the apicomplexan parasite Plasmodium falciparum, the causative agent of malaria, is enabled by the glideosome, a multi-protein complex containing the class XIV myosin motor, PfMyoA. Parasite motility is necessary for invasion into host cells and for virulence. Here we show that milligram quantities of functional PfMyoA can be expressed using the baculovirus/Sf9 cell expression system, provided that a UCS (UNC-45/CRO1/She4p) family myosin co-chaperone from Plasmodium spp. is co-expressed with the heavy chain. The homologous chaperone from the apicomplexan Toxoplasma gondii does not functionally substitute. We expressed a functional full-length PfMyoA with bound myosin tail interacting protein (MTIP), the only known light chain of PfMyoA. We then identified an additional essential light chain (PfELC) that co-purified with PfMyoA isolated from parasite lysates. PfMyoA expressed with both light chains moved actin at ~3.8 m/sec, more than twice that of PfMyoA-MTIP (~1.7 m/sec), consistent with the light chain binding domain acting as a lever arm to amplify nucleotide-dependent motions in the motor domain. Surprisingly, PfMyoA moved skeletal actin or expressed P. falciparum actin at the same speed. Duty ratio estimates suggest that PfMyoA may be able to move actin at maximal speed with as few as 6 motors. Under unloaded conditions, neither phosphorylation of Ser19 of the heavy chain, phosphorylation of several Ser residues in the N-terminal extension of MTIP, or calcium affected the speed of actin motion. These studies provide the essential framework for targeting the glideosome as a potential drug target to inhibit invasion by the malaria parasite.

Publisher URL: http://biorxiv.org/cgi/content/short/127118v1

DOI: 10.1101/127118

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