Type:Protein
SpeciesReactivity:H
B=Bovine;Ca=Cat;Ch=Chicken;D=Dog;EQ=Equine;GP=GuineaPig;H=Human;M=Mouse;P=Porcine;Pr=Primate;R=Rat;Rb=Rabbit;Y=Yeast;Xe=Xenopus;Ze=Zebrafish;;;;NA-NotApplicable;STP=Step-TactinProteins;AllTheneurotrophins,includingNGF,BDNF,NT-3,andNT-4/5constituteagroupofstructurallyrelated,secretedproteinsthatplayanimportantroleinthedevelopmentandfunctionofthenervoussystem.TheBIOLOGicalactivitiesoftheneurotrophinsaremediatedbybindingtothedifferentmembersofthetrkfamilytyrosinekinasereceptors.Threetrkfamilyproteins,trkA,trkB,andtrkC,exhibitingdifferentligandspecificities,havebeenidentified.TrkAbindsNGF,trkBbindsBDNFandNT-4/5andtrkCbindsNT-3.Alltrkfamilyproteinsshareaconservedcomplexsubdomainorganizationconsistingofasignalpeptide,twocysteine-richdomains,aclusterofthreeleucine-richmotifs,andtwoimmunoglobulin-likedomainsintheextracellularregion,aswellasanintracellularregionthatcontainsthetyrosinekinasedomain.Naturalsplicevariantsofthedifferenttrks,includingtrkBvariantslackingthefirstcysteine-richdomain,thefirstandsecondorallthreeoftheleucine-richmotifs,orthetyrosinekinasedomain,havebeendescribed.TheroleofthedifferentextracellularsubdomainsoftrkBinmediatingneurotrophinbindinganddiscriminationiscurrentlybeinginvestigated.Attheproteinsequencelevel,humanandrattrkBaregreaterthan90%identicalandtheproteinsexhibitcross-speciesactivity.TrkBisprimarilyexpressedinthenervoussystem.However,lowlevelsoftrkBexpressionhavealsobeenobservedinawidevarietyoftissues(pancreas,kidneys,ovary)outsidethenervoussystem(Ninkina,N.etal.,1997,J.Biol.Chem.272:13019-13025;Middlemas,D.S.etal.,1991,Mol.CellBiol.11:143-153;Soppet,D.etal.,1991,Cell65:895-903).
