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Cpc1, a Chlamydomonas central pair protein with an adenylate kinase domain.

ABSTRACT: Mutations at CPC1 disrupt assembly of a central pair microtubule-associated complex and alter flagellar beat frequency in Chlamydomonas. Sequences of wild-type genomic clones that complement cpc1, and of corresponding cDNAs, reveal the gene product to be a 205 kDa protein with two predicted functional domains, a single EF hand motif near the C-terminus and an unusual centrally located adenylate kinase domain. Homologs are expressed in mammals (testis and tracheal cilia) as well as ciliated lower eukaryotes. Western blots confirm that Cpc1 is one of six subunits in a 16S central pair-associated complex. Motility defects associated with cpc1 alleles in vivo are partially rescued in vitro by reactivation of axonemes or cell models in saturating concentrations of ATP; thus the Cpc1 complex is essential for maintaining normal ATP concentrations in the flagellum.

SUBMITTER: Zhang H

PROVIDER: S-EPMC1525021 | biostudies-literature | 2004 Aug

REPOSITORIES: biostudies-literature

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Cpc1, a Chlamydomonas central pair protein with an adenylate kinase domain.

Zhang Hui H Mitchell David R DR

Journal of cell science 20040803 Pt 18

Mutations at CPC1 disrupt assembly of a central pair microtubule-associated complex and alter flagellar beat frequency in Chlamydomonas. Sequences of wild-type genomic clones that complement cpc1, and of corresponding cDNAs, reveal the gene product to be a 205 kDa protein with two predicted functional domains, a single EF hand motif near the C-terminus and an unusual centrally located adenylate kinase domain. Homologs are expressed in mammals (testis and tracheal cilia) as well as ciliated lower ...[more]

PMID: 15292403

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Project description:BackgroundFlagella and cilia are fine thread-like organelles protruding from cells that harbour them. The typical '9 + 2' cilia confer motility on these cells. Although the mechanistic details of motility remain elusive, the dynein-driven motility is regulated by various kinases and phosphatases. A-kinase anchoring proteins (AKAPs) are scaffolds that bind to a variety of such proteins. Usually, they are known to possess a dedicated domain that in vitro interacts with the regulatory subunits (RI and RII) present in the cAMP-dependent protein kinase (PKA) holoenzyme. These subunits conventionally harbour contiguous stretches of a.a. residues that reveal the presence of the Dimerization Docking (D/D) domain, Catalytic interface domain and cAMP-Binding domain. The Chlamydomonas reinhardtii flagella harbour two AKAPs; viz., the radial spoke AKAP97 or RSP3 and the central pair AKAP240. Both these were identified on the basis of their RII-binding property. Interestingly, AKAP97 binds in vivo to two RII-like proteins (RSP7 and RSP11) that contain only the D/D domain.ResultsWe found a Chlamydomonas Flagellar Associated Protein (FAP174) orthologous to MYCBP-1, a protein that binds to organellar AKAPs and Myc onco-protein. An in silico analysis shows that the N-terminus of FAP174 is similar to those RII domain-containing proteins that have binding affinities to AKAPs. Binding of FAP174 was tested with the AKAP97/RSP3 using in vitro pull down assays; however, this binding was rather poor with AKAP97/RSP3. Antibodies were generated against FAP174 and the cellular localization was studied using Western blotting and immunoflourescence in wild type and various flagella mutants. We show that FAP174 localises to the central pair of the axoneme. Using overlay assays we show that FAP174 binds AKAP240 previously identified in the C2 portion of the central pair apparatus.ConclusionIt appears that the flagella of Chlamydomonas reinhardtii contain proteins that bind to AKAPs and except for the D/D domain, lack the conventional a.a. stretches of PKA regulatory subunits (RSP7 and RSP11). We add FAP174 to this growing list.

Project description:Success in evolution depends critically upon the ability of organisms to adapt, a property that is also true for the proteins that contribute to the fitness of an organism. Successful protein evolution is enhanced by mutational pathways that generate a wide range of physicochemical mechanisms to adaptation. In an earlier study, we used a weak-link method to favor changes to an essential but maladapted protein, adenylate kinase (AK), within a microbial population. Six AK mutants (a single mutant followed by five double mutants) had success within the population, revealing a diverse range of adaptive strategies that included changes in nonpolar packing, protein folding dynamics, and formation of new hydrogen bonds and electrostatic networks. The first mutation, AK(BSUB) Q199R, was essential in defining the structural context that facilitated subsequent mutations as revealed by a considerable mutational epistasis and, in one case, a very strong dependence upon the order of mutations. Namely, whereas the single mutation AK(BSUB) G213E decreases protein stability by >25 degrees C, the same mutation in the background of AK(BSUB) Q199R increases stability by 3.4 degrees C, demonstrating that the order of mutations can play a critical role in favoring particular molecular pathways to adaptation. In turn, protein folding kinetics shows that four of the five AK(BSUB) double mutants utilize a strategy in which an increase in the folding rate accompanied by a decrease in the unfolding rate results in additional stability. However, one mutant exhibited a dramatic increase in the folding relative to a modest increase in the unfolding rate, suggesting a different adaptive strategy for thermostability. In all cases, an increase in the folding rates for the double mutants appears to be the preferred mechanism in conferring additional stability and may be an important aspect of protein evolution. The range of overlapping as well as contrasting strategies for success illustrates both the power and subtlety of adaptation at even the smallest unit of change, a single amino acid.

Dataset Information

Cpc1, a Chlamydomonas central pair protein with an adenylate kinase domain.

Publications

Cpc1, a Chlamydomonas central pair protein with an adenylate kinase domain.

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