Summary
A bioRxiv preprint reports that Plasmodium male-gamete axonemes retain key surface motility modules but have a reduced set of proteins inside their microtubule doublets. It also describes proteins involved in doublet organization and the progressive assembly of outer dynein arms.
A bioRxiv preprint describes a streamlined internal scaffold in the flagella of Plasmodium male gametes. The researchers report that the axoneme—the structure that supports flagellar movement—retains its main surface-associated motility modules while containing a markedly reduced network of proteins inside its microtubule doublets.
The study combines cellular cryo-electron tomography, high-resolution cryo-electron microscopy, proteomics and parasite genetics to examine the axoneme’s structure and assembly. Its findings address a rapid developmental process: a male malaria parasite can produce up to eight flagellated gametes in approximately 15 minutes, building their motile axonemes from scratch.
A distinct arrangement inside microtubule doublets
Axonemes contain paired microtubules, known as doublets, that form a framework for flagellar movement. Proteins associated with the doublets help organize their structure and support the machinery that generates motion. The preprint reports that Plasmodium retains principal motility modules on the doublets’ surfaces, but has fewer microtubule inner proteins (MIPs)—proteins located within the microtubule structure—than the more extensive internal network described in other axonemes.
The researchers also report a different arrangement at the doublets’ inner junction. Rather than PACRG, this junction is organized by CFAP20 and CFAP52. The study’s genetic experiments found that combined loss of CFAP20 and CFAP52 disrupts doublet integrity and exflagellation, the process in which male gametes emerge from the parasite.
Motor machinery assembles progressively
The preprint identifies a calmodulin protein at the docking region for outer dynein arms. These arms are motor structures associated with microtubule doublets. The researchers report that outer dynein arms accumulate progressively during male gametogenesis, adding an assembly sequence to the structural picture.
Together, the findings describe an axoneme with a reduced internal protein network, a distinct doublet junction and motility machinery that builds up during gamete formation. Because the parasite constructs flagella on a timescale of minutes, mapping these structural features and assembly states helps explain how its male gametes acquire motility rapidly. The report is a bioRxiv preprint.