A‐kinase anchoring proteins are enriched in the central pair microtubules of motile cilia in Chlamydomonas reinhardtii

Abstract

Cilia are microtubule‐based sensory organelles present in a number of eukaryotic cells. Mutations in the genes encoding ciliary proteins cause ciliopathies in humans. A‐kinase anchoring proteins (AKAPs) tether ciliary signaling proteins such as protein kinase A (PKA). The dimerization and docking domain (D/D) on the RIIα subunit of PKA interacts with AKAPs. Here, we show that AKAP240 from the central‐pair microtubules of Chlamydomonas reinhardtii cilia uses two C‐terminal amphipathic helices to bind to its partner FAP174, an RIIα‐like protein with a D/D domain at the N‐terminus. Co‐immunoprecipitation using anti‐FAP174 antibody with an enriched central‐pair microtubule fraction isolated seven interactors whose mass spectrometry analysis revealed proteins from the C2a (FAP65, FAP70, and FAP147) and C1b (CPC1, HSP70A, and FAP42) microtubule projections and FAP75, a protein whose sub‐ciliary localization is unknown. Using RII D/D and FAP174 as baits, we identified two additional AKAPs (CPC1 and FAP297) in the central‐pair microtubules.