chapter  5
15 Pages

Molecular aspects of the centrin-based cytoskeleton in flagellates

ABSTRACT Thesmallcalcium-bindingprotein,centrin,isubiquitiousamongflagellatesandciliates,andappearstoplaysignificantrolesinflagellarbehaviour,feedingandcorticalpatterning.Inthischapter,wepresentacurrentreviewofthemolecularaspects ofcentrin.NumerousflagellateandciliatecentrincDNAshavebeenidentifiedthat encodehomologousproteinsof-20kDa.Allofthesecentrinproteinsconsistoffour calcium-bindingEF-handdomains,ahighlyvariableaminoterminaldomainthatis richinhydrophobicandpositivelychargedresidues,andashortcarboxyterminus. Onlyafewcentringeneshavebeencharacterizedinlowereukaryotes.Ingeneral, centringenesaresimilartoothergenesinagivenspecieswithregardtocodonbias, thepresenceofintrons,thelengthoftheuntranslatedregions,andthepresenceof internaleliminatedsequences.However,thenumberofcentrin-encodinggenesvaries greatlybetweenspecies,raisingtheintriguingquestionastotheroleofcentrin microdiversityinsomeflagellatesandciliates.Also,thepositionofintronsishighly variableincentringenes,anddoesnotconformtotheboundariesofthefunctional EF-handdomains;thissuggestsacomplexevolutionaryhistoryforcentrin. Phylogeneticanalysisdemonstratestheexistenceofthreedistinctcentrinclades:an algalclade,aciliatecladeandadistantlyrelatedcladeconsistingofyeastandoneof theGiardiasequences.Thephylogeneticdata,takentogetherwiththestructuraldata andgenomicanalysis,indicateahighlevelofcentrindiversity.Understandingthis centrindiversitywillbecriticallyimportanttoelucidatingthemechanismsofflagellarbehaviour,feeding,andcortricalpatterninginflagellatesandciliates. Furthermore,understandingtheseprocessesinlowereukaryotesshouldcontribute significantlytoanunderstandingofcentrosomefunctioninhighereukaryotes.