The multiple myosins of malaria: The smallest malaria myosin, Plasmodium falciparum myosin-B (Pfmyo-B) is expressed in mature schizonts and merozoites

Abstract

Myosins are motor proteins which, through interaction with filamentous actin, create movement. Multiple myosins have been identified in many of the apicomplexans, however, little is known regarding provenance over the life cycle or biological function. Six Plasmodium falciparum myosins are known from studies of the genome (Pfmyo-A to Pfmyo-F). The smallest, Pfmyo-B, consists of almost only a motor ‘head’ domain, the part which generates movement; its ‘tail’, generally responsible for cargo-binding or interaction with a substrate is very limited and, similarly, there is no clear ‘neck’ region about which ‘conventional’ myosin movement occurs. Its location and function are unknown. We prepared and characterised a new anti-Pfmyo-B antibody raised against a bacterially expressed protein fragment and show on Western immunoblots that it stains a single band of the predicted size, 88kDa. Using immunofluorescence on mixed asexual stages, we show the protein is most strongly expressed in mature schizonts and merozoites. Merozoite staining lies anterior to the nucleus and varies to a degree between parasites in some showing small particulate inclusions and in others stronger more localised staining. Expression of Pfmyo-B at this developmental stage suggests that it may play a role in red cell invasion.