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Anexo-β-1,3-galactanasegenefromPhanerochaetechrysosporiumhasbeencloned,sequenced,andexpressedinPichiapastoris.Thecompleteaminoacidsequenceoftheexo-β-1,3-galactanaseindicatedthattheenzymeconsistsofanN-terminalcatalyticmodulewithsimilaritytoglycosidehydrolasefamily43andanadditionalunknownfunctionaldomainsimilartocarbohydrate-bindingmodulefamily6(CBM6)intheC-terminalregion.Themolecularmassoftherecombinantenzymewasestimatedas55kDabasedonSDS-PAGE.Theenzymeshowedreactivityonlytowardβ-1,3-linkedgalactosyloligosaccharidesandpolysaccharideassubstratesbutdidnothydrolyzeβ-1,4-linkedgalacto-oligosaccharides,β-1,6-linkedgalacto-oligosaccharides,pecticgalactan,larcharabinogalactan,arabinan,gumarabic,debranchedarabinan,laminarin,solublebirchwoodxylan,orsolubleoatspelledxylan.Theenzymealsodidnothydrolyzeβ-1,3-galactosylgalactosaminide,β-1,3-galactosylglucosaminide,orβ-1,3-galactosylarabinofuranoside,suggestingthatitspecificallycleavestheinternalβ-1,3-linkageoftwogalactosylresidues.Highperformanceliquidchromatographicanalysisofthehydrolysisproductsshowedthattheenzymeproducedgalactosefromβ-1,3-galactaninanexo-actingmanner.However,noactivitytowardp-nitrophenylβ-galactopyranosidewasdetected.Whenincubatedwitharabinogalactanproteins,theenzymeproducedoligosaccharidestogetherwithgalactose,suggestingthatitisabletobypassβ-1,6-linkedgalactosylsidechains.TheC-terminalCBM6didnotshowanyaffinityforknownsubstratesofCBM6suchasxylan,cellulose,andβ-1,3-glucan,althoughitboundβ-1,3-galactanwhenanalyzedbyaffinityelectrophoresis.FrontalaffinitychromatographyfortheCBM6moietyusingseveralkindsofterminalgalactose-containingoligosaccharidesastheanalytesclearlyindicatedthattheCBM6specificallyinteractedwitholigosaccharidescontainingaβ-1,3-galactobiosemoiety.Whenthedegreeofpolymerizationofgalactoseoligomerswasincreased,thebindingaffinityoftheCBM6showednomarkedchange.