Myosin B (MyoB) is one of the two short class XIV myosins
encoded in the Plasmodium genome. Class XIV myosins are
characterized by a catalytic “head,” a modified “neck,” and the
absence of a “tail” region. Myosin A (MyoA), the other class XIV
myosin in Plasmodium, has been established as a component of
the glideosome complex important in motility and cell invasion,
but MyoB is not well characterized. We analyzed the properties
of MyoB using three parasite species as follows: Plasmodium
falciparum, Plasmodium berghei, and Plasmodium knowlesi.
MyoB is expressed in all invasive stages (merozoites, ookinetes,
and sporozoites) of the life cycle, and the protein is found in a
discrete apical location in these polarized cells. In P. falciparum,
MyoB is synthesized very late in schizogony/merogony, and its
location in merozoites is distinct from, and anterior to, that of a
range of known proteins present in the rhoptries, rhoptry neck
or micronemes. Unlike MyoA, MyoB is not associated with
glideosome complex proteins, including the MyoA light chain,
myosin A tail domain-interacting protein (MTIP). A unique
MyoB light chain (MLC-B) was identified that contains a calmodulin-like
domain at the C terminus and an extended N-terminal
region. MLC-B localizes to the same extreme apical pole
in the cell as MyoB, and the two proteins form a complex. We
propose that MLC-B is a MyoB-specific light chain, and for the
short class XIV myosins that lack a tail region, the atypical myosin
light chains may fulfill that role.