The Chlamydomonas flagellar membrane glycoprotein FMG-1B is necessary for expression of force at the flagellar surface

Abstract

In addition to bend propagation for swimming, Chlamydomonas cells use their flagella to glide along a surface. When polystyrene microspheres are added to cells, they attach to and move along the flagellar surface, thus serving as a proxy for gliding that can be used to assay for the flagellar components required for gliding motility. Gliding and microsphere movement are dependent on intraflagellar transport (IFT). Circumstantial evidence suggests that mechanical coupling of the IFT force-transducing machinery to a substrate is mediated by the flagellar transmembrane glycoprotein FMG-1B. Here, we show that cells carrying an insertion in the 5′-UTR of the FMG-1B gene lack FMG-1B protein, yet assemble normal-length flagella despite the loss of the major protein component of the flagellar membrane. Transmission electron microscopy shows a complete loss of the glycocalyx normally observed on the flagellar surface, suggesting it is composed of the ectodomains of FMG-1B molecules. Microsphere movements and gliding motility are also greatly reduced in the 5′-UTR mutant. Together, these data provide the first rigorous demonstration that FMG-1B is necessary for the normal expression of force at the flagellar surface in Chlamydomonas.

Altered N-glycan composition impacts flagella-mediated adhesion in Chlamydomonas reinhardtii

“…1 and Figure 4 -Supplementary Fig. 2) (Bloodgood et al, 2019;Kamiya et al, 2018). Of note, also FMG-1A is localized in flagella and its abundance was unaltered between WT and mutants in vegetative cells (Figure 1 -Supplementary Fig.…”

“…A recent knock down study showed, that it is the main constituent of the glycocalyx surrounding the flagellum. Additionally, a fmg-1B mutant showed a drastically reduced ability to glide (Bloodgood et al, 2019). Strikingly, FMG-1B is present at a high copy number and turns over rapidly within approximately 1 h (Bloodgood, 2009).…”

“…Remarkably, surface iodination experiments in the early 1980s revealed a single protein called flagellar membrane glycoprotein 1B (FMG-1B) as the main player mediating surface contact (Bloodgood and Workman, 1984). FMG-1B is exclusively located in the flagellar membrane and has a remarkable size of around 350 kDa (4389 amino acids) with a large extra-flagellar part (4340 amino acids) anchored in the membrane via a single predicted trans membrane helix of 22 amino acids (Bloodgood et al, 2019). As the name indicates, it is heavily N-and Oglycosylated.…”

Flagella Ca2+elevations regulate pausing of retrograde intraflagellar transport trains in adherentChlamydomonasflagella

“…Elevated cytosolic Ca 2+ triggers a conformational change in Miro, which possesses two Ca 2+ -binding EF-hands, leading to the dissociation of the mitochondrion from the microtubule motor complex 43 . 37 . This allows an adherent flagellum to slide along a surface whilst maintaining contact with it.…”

Prey capture in protists utilizing microtubule filled processes and surface motility

“…This was first described by Ulehla (1911) and later “rediscovered” by Lewin (1952) and Bloodgood (1981). Over time, a number of studies implicated the FMG‐1B flagellar membrane glycoprotein as the key component that mechanically connected force generating machinery inside the flagellum to the flagellar surface allowing traction forces to be exerted on a solid substrate (Bloodgood, 2009; Bloodgood, Tetreault, & Sloboda, 2019). Although it was assumed that a minus‐end directed microtubule‐associated motor protein must be involved in gliding motility, identification of the exact mechanism underlying gliding motility in Chlamydomonas remained elusive until a landmark study by Shih et al (2013) showed definitively that intraflagellar transport (IFT), which had been discovered in Chlamydomonas (Kozminski, Johnson, Forscher, & Rosenbaum, 1993), is the force transduction machinery behind whole cell gliding motility as well as bidirectional, saltatory movement of polystyrene microspheres along the flagellar surface.…”