An axonemal PP2A B‐subunit is required for PP2A localization and flagellar motility

Abstract

Analysis of Chlamydomonas axonemes revealed that the protein phosphatase, PP2A, is localized to the outer doublet microtubules and is implicated in regulation of dynein-driven motility. We tested the hypothesis that PP2A is localized to the axoneme by a specialized, highly conserved 55-kDa B-type subunit identified in the Chlamydomonas flagellar proteome. The B-subunit gene is defective in the motility mutant pf4. Consistent with our hypothesis, both the B- and C-subunits of PP2A fail to assemble in pf4 axonemes, while the dyneins and other axonemal structures are fully assembled in pf4 axonemes. Two pf4 intragenic revertants were recovered that restore PP2A to the axonemes and re-establish nearly wild-type motility. The revertants confirmed that the slow-swimming Pf4 phenotype is a result of the defective PP2A B-subunit. These results demonstrate that the axonemal B-subunit is, in part, an anchor protein required for PP2A localization and that PP2A is required for normal ciliary motility.

Whole Genome Sequencing Identifies a Deletion in Protein Phosphatase 2A That Affects Its Stability and Localization in Chlamydomonas reinhardtii

“…A previous study using sequence similarity indicated that the Chlamydomonas genome contains four potential PP2A catalytic subunits, PP2A-1c (g4366), PP2A3 (g9684), PP2A-c4 (Cre12.g494900), and PPA1 (Cre06.g308350) [34]. Due to the sequence similarities observed among PP2A, PP4, and PP6 in all organisms [32], we asked whether the four Chlamydomonas proteins are PP2A catalytic subunits using phylogenetic analysis.…”

“…It is believed that different families of the B subunit target PP2A to different cellular locations and bind to different substrates [32], [33]. In Chlamydomonas , sequence similarity reveals four catalytic subunits, two scaffold subunits, and five regulatory subunits [34].…”

A FAP46 mutant provides new insights into the function and assembly of the C1d complex of the ciliary central apparatus

“…Since the C1d complex binds to CaM in high calcium, we also compared the effect of loss of FAP46 versus FAP74 on two Ca 2+ -mediated behaviors: phototaxis, in which cells swim toward or away from light; and photoshock, in which a sudden change in light intensity induces a momentary switching from the asymmetrical waveform used during forward swimming to the symmetrical waveform used during backward swimming, rapidly followed by a return to forward swimming (Bessen et al, 1980;Hyams and Borisy, 1978;Kamiya and Witman, 1984;Witman, 1993). Using a simple but sensitive photoaccumulation assay (Elam et al, 2011;King and Dutcher, 1997;VanderWaal et al, 2011), FAP74ami was found to be impaired in phototaxis as previously demonstrated using a more quantitative assay (DiPetrillo and Smith, 2011). Using the same simple assay, both fap46-1 and fap46-1xFAP74ami were severely impaired in the ability to phototax; only the FAP46-rescued strain exhibited WT phototaxis.…”

Integrated control of axonemal dynein AAA+ motors

“…Both the kinases and phosphatases responsible for this reversible modification (Howard et al , 1994; Yang et al , 2000; Yang and Sale, 2000) are integrated within the axonemal superstructure through specific anchoring proteins (Gaillard et al , 2001). These modifying enzymes (casein kinase and 1 and protein phosphatases 2A) directly control the rate of microtubule sliding powered by axonemal dyneins (Gokhale et al , 2009 ; Elam et al , 2011). Similarly, there is evidence that cAMP- and/or Ca 2+ -dependent phosphorylation of the p29 light chain within Paramecium outer arm dynein is directly linked to the control of motor output (Hamasaki et al , 1991; Barkalow et al , 1994).…”