Activation loop phosphorylation of a protein kinase is a molecular marker of organelle size that dynamically reports flagellar length

Muqing Cao, Dan Meng, Liang Wang, Shuqing Bei, William J. Snell, Junmin Pan

Research output: Contribution to journalArticlepeer-review

43 Scopus citations


Specification of organelle size is crucial for cell function, yet we know little about the molecular mechanisms that report and regulate organelle growth and steady-state dimensions. The biflagellated green alga Chlamydomonas requires continuouslength feedback to integrate the multiple events that support flagellar assembly and disassembly and at the same time maintain the sensory and motility functions of the organelle. Although several length mutants have been characterized, the requisite molecular reporter of length has not been identified. Previously, we showed that depletion of Chlamydomonas aurora-like protein kinase CALK inhibited flagellar disassembly and that a gel-shift- associated phosphorylation of CALK marked half-length flagella during flagellar assembly. Here, we show that phosphorylation of CALK on T193, a consensus phosphorylation site on the activation loop required for kinase activity, is distinct from the gel-shift-associated phosphorylation and is triggered when flagellar shortening is induced, thereby implicating CALK protein kinase activity in the shortening arm of length control. Moreover, CALK phosphorylation on T193 is dynamically related to flagellar length. It is reduced in cells with short flagella, elevated in the long flagella mutant, lf4, and dynamically tracks length during both flagellar assembly and flagellar disassembly in WT, but not in lf4. Thus, phosphorylation of CALK in its activation loop is implicated in the disassembly arm of a length feedback mechanism and is a continuous and dynamic molecular marker of flagellar length during both assembly and disassembly.

Original languageEnglish (US)
Pages (from-to)12337-12342
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number30
StatePublished - Jul 23 2013


  • Aurora kinase
  • Cilia and flagella
  • Cilia length
  • Flagellar length control
  • Organelle size control

ASJC Scopus subject areas

  • General


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