IMPORT OF PEROXISOMAL MATRIX AND MEMBRANE PROTEINS

22 Pages·2007·0.43 MB·English

P1:FPP
July11,2000 17:24 AR102 CHAP14
Annu.Rev.Biochem.2000.69:399–418
Copyright(cid:13)c 2000byAnnualReviews.Allrightsreserved
I P M
MPORT OF EROXISOMAL ATRIX
M P
AND EMBRANE ROTEINS
S. Subramani, Antonius Koller, and William B. Snyder
DepartmentofBiology,UniversityofCalifornia,SanDiego,LaJolla,
org California92093-0322;e-mail:[email protected]
s.
w
m arjournals.annualrevie7. For personal use only. oobKnpxfioeeitysgAhrooeeWbmnx2seieont3srribisapdni)ceotsehtrgoraeaxvnoTcieenrthigssboiiassen(ncrpsieeo,nrlvommlietteheeewbeimnciolsslbaegursiaemantrnnvefmeeore.slwaaivPrssei,rsyzdeepeevmrasiionrotbsthuepl,eyisednprurorteraoxvirgniigsergoeewtmswissnahmgilin,capphtdrheoeterhtoieenfixineiofsuluiodnmrmchupteanioovdtrneaterarafgslonetracdtoinunlpdsegseisnersodogigxfoonimsfnaoplamtsenh,ryee-
ded fro10/17/0 mofeptaebrooxliicnsfuinnchtiuomnsanofdpiseeraosxeis(o2m,8e)s,(a1n,d2)in,vasoplveecmtseonftiomfptohret/ebniodgoepnlaessmisi(c3r–e7ti)c,uthluemroilne
wnloago on p(5e,r1o2x)is.oTmhiesmreevmiebwrarneefebrsiotgoesnoemsieso(9f–t1h1e)eaasrliwerelwloasrkthfeordtehgerasdakateioonfionftrtohdisuoctrigoannealnlde
oe
DDi continuity but deals primarily with the more recent progress. The principal areas of
8. n
1a progressaretheidentificationofnewperoxins,definitionofprotein-proteininterac-
4S
99-a - tionsamongperoxinsleadingtotherecognitionofcomplexesinvolvedinperoxisomal
00.69:3aliforni pmroostetiinmipmoprotarnt,cien,stihgehteilnutcoidthaetiobniogoefntehseisroolfepoefromxiasnoymcaolnmseermvbedranpeerporxoitnesinisn,ahnudm,aonf
0C disease.Giventherapidprogressinthefield,thisreviewalsohighlightssomeofthe
ochem. 2ersity of unansweredquestionsthatremaintobetackled.
v. BiUniv
u. Reby
n CONTENTS
n
A
MECHANISMOFPEROXISOMALPROTEINIMPORT ::::::::::::::::::: 400
ImportofMatrixProteins ::::::::::::::::::::::::::::::::::::::::: 400
UnansweredQuestionsRegardingPeroxisomalMatrixProteinImport ::::::::: 404
ImportandAssemblyofPeroxisomalMembraneProteins:::::::::::::::::: 405
UnansweredQuestionsRegardingPMPBiogenesis::::::::::::::::::::::: 409
IsThereaQualityControlPathwayforPeroxisomalMembraneProteins? :::::: 409
InteractionsAmongPeroxins :::::::::::::::::::::::::::::::::::::: 411
HUMANPEROXISOMALDISEASES::::::::::::::::::::::::::::::::: 412
DisordersCausedbyPeroxinMutations::::::::::::::::::::::::::::::: 412
DisordersResultingfromMutationsinProteinsOtherThanPeroxins:::::::::: 413
0066-4154/00/0707-0399/$14.00 399
P1:FPP
July11,2000 17:24 AR102 CHAP14
400 SUBRAMANI ¥ KOLLER ¥ SNYDER
MECHANISMOFPEROXISOMALPROTEINIMPORT
ImportofMatrixProteins
Itisagenerallyacceptedfactthattheimportofmostproteinsintotheperoxiso-
malmatrixissignalmediated.Twoperoxisome-targetingsignals(PTSs),termed
PTS1(aconservedC-terminaltripeptidesequence)andPTS2(anonapeptidese-
quencelocatedneartheNterminusoratinternallocationsinproteins),account
for the transport of most polypeptides into the peroxisome matrix (5; Figure 1).
These signals on matrix proteins are recognized in the cytosol by soluble PTS
g receptors,Pex5pforPTS1proteins(13–20)andPex7pforPTS2proteins(21–28).
or
s. The receptor-cargo complexes then dock at the peroxisomal membrane with the
w
m arjournals.annualrevie7. For personal use only. datdbbepooeirnpecmmPdnkaeaiirinndxeningien1gmat3tolhrppyfoearPnoftiisonsetaetrxpartmih5annptepsseei,acnddtroyPtisbestetotgythxiosrne1uaocb3llsltaepi(pncr3cgeog(2rre1mio)t,t9.hxipc,cTeiylase2htyolxo9eemfes–aoCos3asrl-tw2littc)ethmiw,rteahmCeonbm--PiditnhneebayxPdrrlbma5iepnrnpxiiogend1ara4ttpnsolipyroddosPn(oPtte1eeomex9imfxn5a,7P,pi(3npebP3(xyo(2M–13f9s332Pt–P6pu;)3e)dFc,1xwioi)1eeg.hns3auoTtcpsarshhheiecnioo2soswNn)ffa.tainanwacingtSnhdhiHitnchaC3ghes
ded fro10/17/0 t(h3e2)S.HTh3edsoemstauidnie(s29a–ls3o1s),hoanwdedbythtahtethuesebionfdcinogimomfPuenxo5ppretcoipPietaxt1io3npeisxpdeirreimct.ents
wnloago on It is interesting that the C-terminal SH3 domain of Pex13p is involved in in-
oe teractionswithbothPex5pandPex14p(Figure3).Thereversetranscriptase(RT)
DDi
8. n loopwithintheSH3domainofPex13pinteractswithPex14pviaaPXXPsequence
1a
99-4a - S (atypeII,SH3domain-bindingmotif)onthelatter(32,33,37).Mutationsinthe
00.69:3aliforni
0C MATRIX PROTEINS
ochem. 2ersity of - PTS1 - a C-terminal tripeptide - PTS2 - an N-terminal nonapeptide
u. Rev. Biby Univ HM2NEMBRANECAS HPRKMRLOCOTOEHINe.Sg. Luciferase H2N XXKR LVIX5QHAL COOHe.g. Thiolase
n
n
A
- mPTS COOH COOH
NH2
Cytosol
Matrix H2N COOH NH2 NH2 COOH
20 aa 40 aa 25 aa 55 aa
e.g. CbPmp47p e.g. PpPex3p e.g. PpPex22p e.g. ScPex15p
Figure 1 Targeting signals used by peroxisomal proteins. The PTSs are located in the boxes
alongwiththeconsensussequences,whereapplicable,andconservedvariantsareshownbelow
thesesequences.Ineachcase,anexampleofaproteincontainingthePTSisgiven.
P1:FPP
July11,2000 17:24 AR102 CHAP14
PEROXISOMEPROTEINIMPORTANDBIOGENESIS 401
Pex7p PTS2
Pex5p
Pex7p
g Pex5p
or
s.
w
m arjournals.annualrevie7. For personal use only. CYTOSOL PPeexx153pp PPeexx174p Pex17p
ed fro0/17/0
d1
wnloago on PEROXISOME
oe
DDi
8. n
1a
4S
99-a -
000.69:3Californi Figure2 Modelfortheearlystagesintheimportofperoxisomalmatrixproteins.PTS1-and
v. Biochem. 2University of PrvaesiTsaspShPe2oce-wxtcio1vnn3e,tlpayai.sanTnwindhegelPslpeearxosr1etw4ecipeinpt.shtToaPhrr-eeecxarl3aerpgtct,ooePgrcneofxiomz8remppd,lseiaxnanedtschoibetmiscnepydllfteotx(osnoowtlhtibetsyhhsuosPrpwefeaxncc5)ie.pfiP,coePfrxeet1hxc3ee7ppppt,ofeoPrrsorem,xxPi1sse3ocxpmo5,mpaalpnamldnedexPmePesxbewx1ra77intpphe,,
nu. Reby POelxig5opmaenrdicPpexro1t4epin,sascoshmopwrnis,inbugtsaolmsoewsiuthbuPneixts7pw(idthiraecPtlTySoraninddiortehcetrlys)laacnkdinPgexo1n9epc(annotesnhteorwtnh)e.
n
A peroxisomebecauseproteinunfoldingandmonomerizationarenotessentialforimportofmatrix
proteins.Othercytosolicproteins,PMPs,andintraperoxisomalproteinsimplicatedinimportare
describedinthetext.
RTloopofPex13pthatdisruptinteractionswithPex14pdonotimpairtheability
of Pex13p to interact with Pex5p. Thus, the binding interactions of Pex5p and
Pex14pwiththeSH3domainofPex13pmustbeatleastpartiallynonoverlapping
(32).NoPXXPmotifhasbeenfoundonPex5p,sothepeptidesequencesinvolved
inthePex5p-Pex13pinteractionremainobscure.Onecannotruleoutthepresence
ofnoncanonicalbindingsitesforSH3domainproteinsasdescribedrecentlyfor
theinteractionofanSH3proteincalledEps8withaPXXDYsequence(38).
P1:FPP
July11,2000 17:24 AR102 CHAP14
402 SUBRAMANI ¥ KOLLER ¥ SNYDER
4
10
1 6
22 22
12 2 19 3
13
ws.org BDionmdaining ADctoimvaatiinon (SH3) 17
m arjournals.annualrevie7. For personal use only. IPPnTetreSigp-rrhaeelcr ePaplM tpoPrrossteins 5 14 7IP1 34 & 8
ed fro0/17/0 tFoirgius,rbeu3tmIanntyeroafcttihoensseaimntoernagctpioernosxhinavs.eTahlseoinbteeernacdteiotencsteadreindeortihveerdsfyrsotmemdsa.taonP.pas-
d1
wnloago on
oe
DDi IncontrasttothedirectbindingofPex5ptoPex13p,itisnotknownwhetherthe
18. an interaction between Pex7p and Pex13p is direct or indirect. These two proteins,
4S
99-a - Pex7pandPex13p,fromSaccharomycescerevisiaeinteractintheyeasttwo-hybrid
00.69:3aliforni sthyestaebmseinncweioldf-Ptyepxe5pstraanidn/soarnPdeaxr1e4fpou(3n2d)t.oFguertthheerrimnocroei,momveurnexopprreescsipioitnatoefsPeevxe1n3ipn
0C
ochem. 2ersity of swNui-pttheprrPmeesixsne1as4lapdodcmeafnaeicsnttiivolleffPPoeerxmx173pap.cFo(inmnoaptlllteyhx,ebwCeci-ttaheurPsmeeixPn7eapxl,1Si3Htp3hmadsuobtmaenaetinsn)tshufaogtrgmfeasistleatdoctiohnmatetprtlahecxet
v. BiUniv withPex7p(32).
nu. Reby PexP8epx,1P4epxf1o3rpm,sancodmPpelxe1x7epsw(3i2th,3s3e,v3e9ra;lMprAotJeoinhsn,ssounc,hWasBPSenxy3dpe,rP,eMx5Vpe,ePnehxu7ips,,
n
A SSubramani,JCregg,unpublisheddata;Figure3).Theseinteractionshavebeen
detectedusingtheyeasttwo-hybridsystem(32,33,37;MAJohnson,WBSnyder,
M Veenhuis, S Subramani, J Cregg, unpublished data) and in coimmunoprecip-
itated complexes (32,33,39; MA Johnson, WB Snyder, M Veenhuis, S Subra-
mani, J Cregg, unpublished data). Pex14p appears to be peripherally associated
withtheperoxisomalmembraneinyeasts(32,33,39;MAJohnson,WBSnyder,
M Veenhuis, S Subramani, J Cregg, unpublished data), although in mammalian
cellsitbehavesasanintegralmembraneprotein(19,36).InS.cerevisiae,inwhich
Pex14pappearstobeaperipheralPMP,itwasfound(32)thatPex14pwascytoso-
licincellslackingPex13p,suggestingthatPex13pmightanchorPex14ponthe
peroxisomalmembrane,inadditiontoitsotherfunctions.However,theinteraction
P1:FPP
July11,2000 17:24 AR102 CHAP14
PEROXISOMEPROTEINIMPORTANDBIOGENESIS 403
betweentheSH3domainofPex13pandthePXXPmotifofPex14pwasnotnec-
essaryfortheassociationofPex14pwiththeperoxisomalmembrane.Whenthis
study was published, Pex14p was known to interact with only two other PMPs,
Pex13pandPex17p.Inlightofthisinformation,itseemedsurprisingthatS.cere-
visiae Pex14p was still associated with the membrane of peroxisome remnants
eveninpex131/pex171cellsexpressingaPex13pmutant(Pex13p-E320K)that
could not interact with Pex14p. However, in view of more recent data showing
that Pex14p can also form complexes with other integral PMPs, such as Pex3p,
the association of Pex14p with the peroxisomal membrane is likely to be me-
diated by multiple interactions, such as those with Pex3p, Pex13p, and Pex17p
g
or (39).
s.
w Recent experiments in Hansenula polymorpha show that Pex14p is partially
m arjournals.annualrevie7. For personal use only. poPp(TMhfhehxooePA1srseype4xJlhpoa1roeht4wersnpyduistllhohaftosantcesr,sedmWuartoglaosBngiofneSSPsboneteetryxthe/hd1Tneae4rhtdrppr,ce,eMremrwerostoVhaxindeieinsnuretesenria.nashsPttu(eeeP4idrxse0a,1xac)S3.nt1ipId7SonpnuaaPpsbpinpripbcateeeehmaatrirwaraasscnetptietos,aonJiswnrtpCeotieetgrrhrreiuoasgblxc,agotitt,nhteohusentnfhlcppoyeahurnwomibnsbilsttpieehshorhrtofaeehcrPgdeytueildpoxalahant1titoa4oeos)pnd-f.
ed fro0/17/0 byPpreoxt1e4inpmisopdreifisecnattiionnas.membrane-associatedcomplexwithPex17p(32,39,41),
d1
wnloago on Pw.hpiachstoarpipse,aPresxt1o7bpehaaspaersiipnhgeleratlramnesmmbemranbreapnreodteoimnaininSa.ncderaetvoipsioaleo.gHyocwonesviesrt,enint
oe
DDi withanN-terminallumenaldomainandacytosolicC-terminalregion(39).The
18. an C-terminaldomainhastwocoiled-coilregionsofunknownfunction(39,41),which
4S
99-a - maymediateinteractionswithotherperoxinscontainingcoiledcoils,suchasPex3p
00.69:3aliforni apnedroPxeisxo1m4pe.sAanltdhoisugahcoPmexp1o7npenistnoefetdheedpfeorroxthiseoimmep-oarstsoofcimataetdrixdopcrkoitnegincsoimntpoltehxe,
0C
ochem. 2ersity of emitffiehmcaisbernreatcnieemn.ptTloyhritbseoseftnusdesvyheosrwhaolnwPiMnstPPh.sa,ptasPusetcxoh1ri7assptPhaaelstxo3thphiasasnpadrorPtoeeliexn2iin2sptah,letsooimtrhepeqoupriterroeodfxafitsoorlemtahasetl
v. BiUniv some,ifnotall,PMPs,leavingopenthepossibilitythatthematrixproteinimport
nu. Reby dPeMfePctiminppoerxt1(7319).mutantsisatleastpartiallyasecondaryconsequenceofimpaired
n
A OtherPMPsinvolvedinmatrixproteinimportincludethreezinc-bindingring-
fingerproteins,Pex2p,Pex10p,andPex12p(5),aswellasPex15p(42),Pex22p
(43), and Pex23p (44). At least one intraperoxisomal protein, Pex8p, is also re-
quiredforimport(45,46).ThisproteinhasaPTS1sequenceinS.cerevisiaeand
P. pastoris (45) and a PTS2 sequence in H. polymorpha (46) and is found in a
complexwithotherperoxins,suchasPex14p(MAJohnson,WBSnyder,MVeen-
huis,SSubramani,JCregg,unpublisheddata)andPex5p(46a),butitsroleinthe
importofmatrixproteinsisnotyetunderstood.
Othercytosolicproteinsinvolvedinmatrixproteinimportincludeheatshock
proteins of the DnaK (hsp70) (47) and DnaJ (Djp1p) (48) families. The hsp70
proteinbindsandhydrolyzesATP,providingatleastapartialexplanationforthe
P1:FPP
July11,2000 17:24 AR102 CHAP14
404 SUBRAMANI ¥ KOLLER ¥ SNYDER
ATP requirement during the import of peroxisomal matrix proteins. The precise
roles for the heat shock proteins remain a mystery, especially because protein
unfolding is not a prerequisite for matrix protein import (49–51). Additionally,
Pex18pandPex21parerelatedcytosolicproteinsthatexistinacomplexwiththe
PTS2receptor,Pex7p,andplayaroleintheimportofPTS2proteins(52).Because
Pex18pandPex21parerelated,theymayfulfilloverlappingfunctions.Consistent
withthisviewistheobservationthatdeletionofeitherthePEX18orthePEX21
gene does not impair PTS2 protein import but deletion of both genes does. Yet
anothercytosolicprotein,Pex20p,interactswithapartofamatrixprotein,thiolase,
that is outside the PTS2 region and is necessary for the dimerization of thiolase
g
or anditsimportintotheperoxisomematrix(53).
s.
w Previousstudieshaverevealedthatproteinunfoldingisnotobligatoryforthe
m arjournals.annualrevie7. For personal use only. tpmmofrorraiaoungtPtnrsheeidpitxxno.i7wsrnpItonctonahdufdneenpeedotroderrla,rwgyvtapchehneeryeepsrrtletetaliheditenahemrseePcaiiTpntrrreceStiorupxomortxehrrescitesstpeaoprpnomeetcfsoraeeortlsnsxhtmie(as1froeuoe6mmnc,ncc2ebuto2rimrato,rn2naetert3anarl)cin(.xe4osW9rp(o5–odfh45rete,1iaent5)ddht5.-re)eaIirnnnpattdenohvrdeoiitentxhwhPtieeasTrotompSmofeelrraitdoeghlicxoiaPseimts,peeoxsteoomr5niripncees
ed fro0/17/0 tthheePnoTrSmraelciemptpoorrstacryecplerimisaarnilyopceyntoqsuoeliscti(o1n7.,I2n0t,h2e4m–2a6jo,r3i0ty,5o6f).reTphoirstsr,eqhuoiwreesvearn,
d1
wnloago on apcritoivretomtehcehatrnainsmsloocfatdioisnsoocfiathtieonPTofS-tchoenPtaTinSinpgropterointesinfroamcrotshseitrherepceeprotoxrisso(m57a)l
oe
DDi membrane,butthedetailsofthisprocessareunknown.
18. an Although folded and oligomerized proteins can enter the peroxisome lumen,
4S
99-a - thereisevidencethatnotallproteinsarefullyassembledwiththenecessarycofac-
00.69:3aliforni toofraslpcorihoorltooxthideairseenatrreyiminptoorpteerdoixnitsoompeersox(5is8o)m.Ietshoasfmbeeetnhyreloptorortpehdicthyaetamstosn,owmheerres
0C
ochem. 2ersity of tmihneatrytaicpraeelrqloyuxiarisecotitmvheealocccohtfaaampceteorrorsnF(eA5s9.DR,6ea0cn)ed.nTatlnhye,usthneecsrhteuawrdaiacestsearhirazevepedohrctihnoatfpehdesrpaot7n0etheteoxeisfxotiirsnmtgeniencnsezidyoe-f
v. BiUniv glyoxysomesofwatermelons(61).Thisisaninterestingexampleofasinglegene
nu. Reby ainnidtiamtoRrNAAUGapcpoadreonntsl.yTgreanneslraattiionngftrwoomptrhoetefiirnsstAbyUtGrayniselladtisoanlofrnogmertpwroesdeiqffueernecnet
n
A thattargetsreporterstothewatermelonproplastids.Translationfromthesecond
AUGyieldsashorterpresequencewithaPTS2thatisabletofunctioninperoxiso-
maltargetinginH.polymorpha.ThisPTS2sequenceisapparentlynonfunctional
inthecontextofthelongerpresequence(61).
UnansweredQuestionsRegardingPeroxisomal
MatrixProteinImport
Despitetheprogressindefiningthecytosolicandperoxisomemembrane-associ-
atedcomponentsnecessaryfortheimportofmatrixproteins,thereremainmany
questions regarding this process. Why do the PTS receptors interact with two
P1:FPP
July11,2000 17:24 AR102 CHAP14
PEROXISOMEPROTEINIMPORTANDBIOGENESIS 405
docking proteins, Pex13p and Pex14p, and do the interactions with the docking
proteinsoccurinasequentialorsimultaneousmanner?IsthePTSreceptordocking
complexdistinctfromthemachinerythatallowsproteintranslocationacrossthe
peroxisomalmembrane?Whatisthenatureofthetranslocationintermediate,and
do the proteins traverse a pore or channel as they cross the membrane? How
do the PTS receptors catalyze multiple rounds of import? What are the specific
ATP-requiring steps in import? What roles do chaperones or factors involved in
proteinoligomerizationorassemblyplay?Whatisthefunctionofintraperoxisomal
peroxinsinmatrixproteinimport?
g
s.or ImportandAssemblyofPeroxisomalMembraneProteins
w
m arjournals.annualrevie7. For personal use only. FeriponerrnogagolrlaytesprPcidirgnMooinnsmtePag(mil4snsth2,osme,nct4uaomf3slelt,beaece6btduh2eiramm–enp6epior4smeofm)srmbet(erFnoPadtifTngaiieuSnnsrstsPeoteihTsm1teSha)b.sepslUeyt(prrmeneootlrfxPciokihPTxseMoSiostmfsohP)6mea,sl.ttemohTmam8ohterebamehsaterahbsiviixrPcgea,MhnatblemhPye;eesictnnihhonoiandtsavesecgerefiiarrddnaivssielesed(dats4inni2Pqdnc,Tut6pseSt2eesas,vtrr,ii6geopt4rehnhat)es--l.
ed fro0/17/0 Tmhael mmPemTSbsraanree,oafntednthoeriyenmteadyt(o4p2o,l4o3g)icoarllymoanytnhoetlu(6m2e–n6a4l)siindceluodfethaenpaedrojaxcieson-t
d1
wnloago on tranTshmeepmatbhrwanaeysoefgimmepnotr.tofPMPsisdistinctfromthematrixproteinimportpath-
oe
DDi waysbecausemanypexmutantsaffectthelatterbutnottheformer.Furthermore,
18. an invitroimportstudiesshowthatperoxisomalmatrixandmembraneproteinshave
4S
99-a - distinctbiochemicalcharacteristics,suchastherequirementforATPfortheim-
00.69:3aliforni poofrpteorfoxmisaotrmixaplrmotaetirnixsa(6n5d–m67e)m.Tbrhaeneexpisrotetneicnesoifssaedpiasrtaintegpuaisthhiwnagyfsefaoturrtehethiamtpseotrst
0C
ochem. 2ersity of pBpeoerscotatxruiassneosmlmaatailnopynraoPltlMeyinfPrssoomarrteitnhbgeecalypietaovrsetodfrlotdomirbetechtelsyytrntaotnhtshepseoipzreterdoofixpnirsotohtmeeianclysmttooesmootlbhareanrndoerig(m6a6np–eol6rlt8ees)d,.
v. BiUniv there must be mechanisms by which the hydrophobic transmembrane segments
nu. Reby omnecthheanPisMmPssinavroelvperodteincttehdisapnrdocpersesveanretecdomfropmletealgygurengkantoinwgni.n the cytosol. The
n
A ThereareonlyafewmutationsinyeastandmammaliancellsthataffectPMP
import. The pex3 mutant apparently lacks all peroxisome remnants in yeasts
(63,69,70).ThesedataplacePex3pattheearlieststagesofperoxisomebiogenesis,
duringwhichtimeitspresenceisessentialfortheformationofdetectableperox-
isomeremnants,whichareassumedtobeprecursorsofthematureperoxisomes
(Figure4).However,themechanismofinsertionofPex3pintothemembraneof
remnantsisnotunderstood.Pex3pappearstobeaproteinwithasingletransmem-
branedomain,acytosolicCterminus,andalumenalN-terminalsegment,thefirst
40 amino acids of which contain a mPTS (63,64). The cytosolic domain has a
putativecoiled-coilmotifthatmaybeinvolvedinprotein-proteininteractionswith
Pex14pandPex17p.
P1:FPP
July11,2000 17:24 AR102 CHAP14
406 SUBRAMANI ¥ KOLLER ¥ SNYDER
Figure4 Workingmodelforearlystages Pex3p
in the biogenesis of peroxisomes, show-
ingthestagesatwhichthethreeperoxins,
Membrane Pex17p
Pex3p,Pex17p,andPex19p,necessaryfor proteins Early remnant/
early-pre-peroxisome
PMPimportand/orassemblyact.Seetext
fordetails. Pex19p
Late remnant/
g late-pre-peroxisome
or
s. Other
w
m arjournals.annualrevie7. For personal use only. peroxins MpMroaattretuiixnres peroxisome
ed fro0/17/0
d1
wnloago on The cytosolic domain of Pex3p is positioned correctly to interact with a per-
oe
DDi oxin,Pex19p,whichispredominantlycytosolicinmostspeciesandonlypartially
18. an peroxisomeassociated(71–74).Inmostspecies,Pex19pisfarnesylatedattheCin
4S
99-a - aC-terminalCAAXmotif(71,73,74).However,thefarnesylationisnotnecessary
00.69:3aliforni f(o7r1)i.ts functions in P. pastoris (72), nor is it absolutely required in S. cerevisiae
0C
ochem. 2ersity of tohfetIrhneewSP.e.rcpeearnseotvoidrsieisatepecetaxan1bd9le1inpechreoullxmsisabonympdeaetcrieoemnnvtnocalenulttlsiso(ln7a1cm,k7iicn4rg)o.sHtchooepwPyeEvhXears1,9icnagdreeenfeudelrpaernvoaedlayulsceitds,
v. BiUniv novelvesiculotubularremnantslabeledwithanti-Pex3pantibodies(72).Thus,tar-
nu. Reby gAestsinugmionfgPt.haptatshtoesreisPPeexx33pp-ctoonttahienimngemstbruracntuersesoffotuhnedrienmtnhaenptsexi1s9s1tilml puotasnsitbalree.
n
A normal intermediates in peroxisome biogenesis, they represent a novel structure
calledearlypreperoxisomes,becausetheyaresmallerinsizethantheother“late
preperoxisomes” that accumulate as remnants in most other pex mutants. This
placesoneofthesitesofactionofPex19pattheearlypreperoxisomemembrane,
whereitsinteractionwithPex3ppresumablyoccursandisnecessaryforthecon-
versionofearlypreperoxisomestolatepreperoxisomes(Figure4).Weusetheterm
preperoxisometorefertointermediatescommittedtobecomingperoxisomes,and
nototherorganelles,inwild-typecells.
An important clue to the possible function of Pex19p is that it interacts with
manyotherPMPsinbothyeastandmammaliancells(Figure3)(39,72;KSack-
steder, J Jones, SJ Gould, personal communication). In P. pastoris, it interacts
P1:FPP
July11,2000 17:24 AR102 CHAP14
PEROXISOMEPROTEINIMPORTANDBIOGENESIS 407
withthePMPsPex2p,Pex3p,Pex10p,Pex13p,Pex17p,andPex22p(39,72).By
analogy to the PTS receptors Pex5p and Pex7p, which are mainly cytosolic and
partially peroxisome associated, it seems plausible that Pex19p shuttles PMPs
fromtheirsiteofsynthesisinthecytosoltotheperoxisomemembrane.Thishy-
pothesis suggests that Pex19p might be the mPTS receptor. Preliminary results
indicatethatPex19pinteractswiththecytosolicdomainsofseveralPMPs(such
as Pex3p, Pex13p, and Pex22p) rather than with the lumenal mPTSs (72; WB
Snyder, A Koller, S Subramani, unpublished data). These results make it more
likely that Pex19p is not the mPTS receptor but rather is an assembly factor for
PMPs, facilitating the conversion of early to late preperoxisome intermediates.
g
or However,itremainstobeprovenwhetherPex19interactswithitspartnersinthe
s.
w cytosolorattheperoxisomemembraneinvivo.
m arjournals.annualrevie7. For personal use only. awPCdnoe-idxttmThe1iraht9mtisehpnriiesennwatCiiessli-trhdataceoceqrmtrmmuitoaaaaininnlininyatwlaly(,toi3itcntvh9hyee,eotc7dorte2hisspfo)esfe.rleairArrcPoeyMxln,stihcetnPhgeossimu,bs.geseTshtunuhwctgmeheogeNofeanrs-sePttteshePdrxetmeeh3xtiaaipn1nit.t0laeetIplrhdnasecaemctngroioodamnplnteePpronaeionfstxftgPo1,tf7ehtoxhpPef1e,etP9xhoipen1ecxt9cwei1upnri9rattisphecnr/ttvPPiaeoiceeranatxxico33iottnppssf
ed fro0/17/0 ipnotsesriabcitliiotyn,mcoanysibsetednitswtinitchttfhreosmedthaetaianntedrathcetiorenqoufirPemexe1n9tpowfPitehx3opthfeorrPthMePesa.rOlienset
d1
wnloago on sotxaigseosmoefmpeermoxbirsaonmeefobrioPgeexn1e9spis.,OisnctheaPtePxe1x93ppiissathsseodcoiactkeidngwiptrhottheienpoenrotxhiesopmere-
oe
DDi membraneinthismanner,itcouldtheninteractwiththeotherPMPsviaadiffer-
18. an entdomain,asachaperoneorassemblyfactor,tofacilitatetheirassemblyduring
4S
99-a - the conversion of early preperoxisome intermediates to the late preperoxisomes
00.69:3aliforni (FigAurthei4rd).componentinthebiogenesisofPMPsisPex17p,whichwasdescribed
0C
ochem. 2ersity of eIsneavrPlei.rearplaaPssMtoaPrisssu(,bPmuenxui3ttapon,ftPsethxlae2c2kmpin,aatgrnidxPePpxer1xo71tep0ipna)ritemoprpeaomrrttinacalonlymt-ldpikelefeexsctitrniuvceSt.uinrceestrh(e3ev9isi)mi.aPpeeox(r41t17o)pf.
v. BiUniv formscomplexeswithPex3p,Pex14p,andPex19p,andexistsinseveraldistinct
nu. Reby sliunbkceorsm)pinlevxoelvsin(ogrPceoxn1f7oprm(3a9t)i.oTnahlesptraetseesn,caesodfePteexc3tepdinbiymamcucensospibreilciitpyittaotecsrwositsh-
n
A eitherPex14porPex17phadnotbeendetectedearlierinS.cerevisiaebecausemost
ofthecomplexeswerestudiedafterimmunoprecipitationofPex7p(32,41).There
are separable pools of Pex3p in complexes with Pex14p, Pex17p, and Pex19p
andofPex17pincomplexeswithPex14pandPex19p.Similarly,thereappearto
beseparablepoolsofPex17pinassociationwitheitherPex5p-Pex7p,Pex3p,or
Pex19p(39).
Itisinterestingthat,intheabsenceofPex19p,severalotherPMPs,suchasPex3p
and Pex22p, are in the membranes of remnants (72; WB Snyder, S Subramani,
unpublisheddata).Thus,Pex19pisnotinvolveddirectlyintheinsertionofPMPs
inthemembranebutratherparticipatesinastepaftermembraneassociation.In
contrast,Pex17phasafunctionasanassemblyfactorbeforemembraneinsertion
P1:FPP
July11,2000 17:24 AR102 CHAP14
408 SUBRAMANI ¥ KOLLER ¥ SNYDER
of PMPs, because in its absence several PMPs remain partially cytosolic (39;
Figure4).ItremainstobeseenwhetherPex17palsohasaroleinPMPassembly
afteritsownassociationwiththemembrane.
Afourthcomponent,Pex16p,hasbeenimplicatedinPMPimport.TheYarrowia
lipolytica pex161 mutants are partially deficient in the import of a PMP, Pex2p
(75).Unfortunately,theimportofotherPMPshasnotbeenanalyzedinthisstrain.
Thepex161mutantisalsoimpairedintheimportofsomematrixproteins,suchas
isocitratelyase,thiolase,andcatalase,butnotothers(acyl-CoAoxidaseandpro-
teinsrecognizedbyananti-SKLpeptideantibody).InY.lipolyticastrainslacking
functionalPex16p,thereisanaccumulationofclusteredvesicularstructuresthat
g
or are40to50nmindiameter,andoccasionallylargerones(100to150nmindiam-
s.
w eter),thatarelabeledforperoxisomalmarkers,suggestingthattheyareremnants.
m arjournals.annualrevie7. For personal use only. PimPannEEdidgXXAirhP1e1tEhc62hutX-(ammi7vm16aye3m)nc-e.m,usIcPncnyeMaolctlphfl)Peliauis3dnro2ecerde-enemflsolrtceoytlecimcinntm,iecoAa,pennLo,ZobrbDetuyedlPtldew,tihtPtieenis7csgth0toetaoRerbnuc,slolhePdyrnmnEpbideqXearrulnoo3epomx-.metiNeesryoodopcxmtta,ihasetPbaioeErtlmyensX,mtmes1wsnae0iavla-nlnesm,ttrvmhsayeelwcsuP,hitecPaMurutEemelPXaddasren1irt(n1eePP(cid:11)mchMEt-uenXmPmda17ynba60ctyns-,,
ed fro0/17/0 dtreufilyciceynttolsionleisc.oHroawreeavsesro,citiaretemdawinisthusnmcearltlarienmwnhaentthsetrhtahteasreeubneiymonpdorttheedrPeMsoPlustiaorne
d1
wnloago on lfiomunitdoifncYo.nlviepnotliyotnicaallmiguhttanmtsiclraocskcionpgyP.Aexs1n6opt.edabove,suchremnantshavebeen
oe
DDi AlthoughnoremnantsweredetectedinthePEX16-deficientcells,transfection
18. an or microinjection of these cells with the PEX16 cDNA resulted in the restora-
4S
99-a - tionofnormalperoxisomes.Interestingly,atemporalanalysisoftheaccumulation
00.69:3aliforni oenfcvoadriinogusPmEXat1ri6x-manydcrmeveemablerdantehamttahrekeimrspionrtcoefllPsEmXic1r6o-imnjyecctiendtowpiuthnctthaetecsDtrNucA-
0C
ochem. 2ersity of t(nu7ar6se)cs.eTpnrtheepcsreeedpdeeadrtoathxaeisreiommcpoeonsrst(iasotrfeisnPitnMwgPift7rho0maamnudontdchehalatritnahcweteihrmiiczpheodPrtaEonXfd1cp6aetaarhclaacspuesmouucnlcacutoermrsefimdrlisatttteiendr
v. BiUniv precursormembranes),allowingtheefficientimportofotherspecificPMPs.The
nu. Reby ethxeacntasrecleanttiopnreshpieprooxfitshoemseeshtyoptohteheeatirclayla,nmdalmatmeparlieapnerporxeicsuormsoersmobesmebrvraendeisnaynedasotsf
n
A (72)isnotclearatpresent.Wedonotknowatpresentwhetherthetwootherperox-
insinvolvedinPMPinsertionintomembranes,PEX3andPEX17,areincorporated
intothemembranesofuncommittedprecursormembranesornascentpreperoxi-
somesbefore,during,orafterPEX16.Inyeasts,oncetheearlypreperoxisomeis
assembled, the action of Pex19p and its interactions with multiple PMPs would
rearrangeorassemblethePMPsinthemembranesoftheearlypreperoxisomesto
allow their maturation to late preperoxisomes. These late preperoxisomes accu-
mulateaslateremnantsinseveralmutantslackingsomecomponentofthematrix
protein import machinery. When this machinery is functional, import of PTS1-
andPTS2-containingproteinswouldallowtheconversionoflatepreperoxisomes
tomatureperoxisomes.