HtrA4isasecretedhumanserineproteaseissupposedtoformoligomersofidenticalproteinchainsasrevealedbyX-rayanalysisforthebacterialHtrAproteinDegP[1].PolypeptidechainsofhumanHtrA4consistofseveraldomains:AnN-terminalinsulin-likegrowthfactordomainisfollowedbyaKazal-typeserineproteaseinhibitordomain,alinkerregion,atrypsin-likeproteasedomainandaPDZdomain[2].ThetruncatedversionHtrA4DcoverspartoftheKazaldomain,theserineproteaseandthePDZdomain.ThefunctionofHtrA4isaprobableserineprotease.Noinformationisavailableyetonphysiologicalsubstratesorinteractingproteins.

Purity:RecombinantHtrA4appearsasamajorproteinofabout38kDainSDS-PAGE(>90%oftotalprotein).DuetominorN-terminaltruncationoftheproteinitmayappearasadoubleband.

EnzymaticActivity:ProteolyticactivityofrecombinanthumanHtrA4isdocumentedbydigestionofß-casein. 0.5mgß-casein/mlarecompletelydigestedby10μg/mlHtrA4within24hoursat37°C(seePDFinsert).

StABIlity&Storage:RecombinanthumanHtrA4isstableuntiltheexpirydategivenonthelabelwhenstoredat-70°C.Repeatedfreezingandthawingshouldbeavoided.Note:Uponfreezing,afaintprecipitatemayformwhichcontainsHtrA4.ThisprecipitatewasshowntocontaincatalyticallyactiveHtrA4inacaseindigest.Therefore,werecommendvortexingtheproteinsolutionbeforeuse.

Applications:RecombinantHtrA4allowdetailedstudiesofthestructureandfunctionofthisprotease.Theenzymeisusedtoscreenforinhibitorsandtocharacterizeinhibitoractions.RecombinantHtrA4canalsoserveasstandardinenzymaticandimmunochemicalassays.