The flagellar motility of Chlamydomonas pf25 mutant lacking an AKAP-binding protein is overtly sensitive to medium conditions.
Radial spokes are a conserved axonemal structural complex postulated to regulate the motility of 9 + 2 cilia and flagella via a network of phosphoenzymes and regulatory proteins. Consistently, a Chlamydomonas radial spoke protein, RSP3, has been identified by RII overlays as an A-kinase anchoring protein (AKAP) that localizes the cAMP-dependent protein kinase (PKA) holoenzyme by binding to the RIIa domain of PKA RII subunit. However, the highly conserved docking domain of PKA is also found in the N termini of several AKAP-binding proteins unrelated to PKA as well as a 24-kDa novel spoke protein, RSP11. Here, we report that RSP11 binds to RSP3 directly in vitro and colocalizes with RSP3 toward the spoke base near outer doublets and dynein motors in axonemes. Importantly, RSP11 mutant pf25 displays a spectrum of motility, from paralysis with flaccid or twitching flagella as other spoke mutants to wildtype-like swimming. The wide range of motility changes reversibly depending on the condition of liquid media without replacing defective proteins. We postulate that radial spokes use the RIIa/AKAP module to regulate ciliary and flagellar beating; absence of the spoke RIIa protein exposes a medium-sensitive regulatory mechanism that is not obvious in wild-type Chlamydomonas.
Yang
Chun
C
Department of Biological Sciences, Marquette University, Milwaukee WI 53233, USA.
Yang
Pinfen
P
D048868:Adaptor Proteins, Signal Transducing / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D025041:Animal Migration / Q000187:drug effects; D000818:Animals; D001483:Base Sequence; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism* / Q000502:physiology; D017124:Conserved Sequence; D003470:Culture Media / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D005407:Flagella / Q000187:drug effects* / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D010940:Plant Proteins; D011485:Protein Binding; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D048868:Adaptor Proteins, Signal Transducing; D003470:Culture Media; D010940:Plant Proteins; D015800:Protozoan Proteins; C060324:radial spoke protein, Chlamydomonas; D017868:Cyclic AMP-Dependent Protein Kinases