Fig 7. Schematic cartoon summarizing the complex interplay of factors leading to sporozoite motility.

Actin modulators such as profilin (this study) or coronin [30] influence the state of actin by either promoting or preventing filament formation, filament crosslinking and filament orientation. The actin state influences retrograde flow and force generation as revealed by the use of inhibitors or mutants. Motility is the outcome of a non-trivial interplay between retrograde flow and force as these are not perfectly inversely correlated. Hence we stipulate the existence of another unknown factor that influences the actin state to produce optimal motility. The system is robust within a certain range (red dashed line), while unbalancing one or several of these factors leads to aberrant motility.