title: Xylan-degrading enzymes from Aspergillus terreus: Physicochemical features and functional studies on hydrolysis of cellulose pulp.
abstract: Two endo-β-1,4-xylanases named XylT1 and XylT2, previously purified from Aspergillus terreus, were structurally investigated by fluorescence quenching and characterized with respect to their binding properties with phenolic compounds. Neutral and charged quenchers had access to both enzymes in neutral and alkaline pHs. The greatest access was noted for the negative quencher, possibly due to positive amino acid residues in the vicinity of tryptophan. These tryptophan environments may partially explain the conformational differences and lower binding constants of phenolic compounds for XylT2 than XylT1Phenolic compounds had lower binding constants for XylT2 than XylT1. These results show that xylanases present structural and functional differences, despite belonging to similar families. XylT1 and XylT2 were also evaluated for their ability to hydrolyze cellulose pulp in different stages of bleaching. Both enzymes promoted hydrolysis of cellulose pulps, which was confirmed by the release of total reducing sugars, pentoses and chromophoric material. Analysis of released xylooligosaccharides demonstrated a preferential release of xylobiose. None of xylanases released glucose, showing that they do not hydrolyze the cellulose present in the pulp, making both enzymes excellent choices for bio-bleaching applications.
authors.affiliation: Laboratory of Enzymology, Department of Cellular Biology, University of Brasília, Brasília 70910-900, DF, Brazil. Electronic address: leonorarsm@gmail.com.
authors.forename: Leonora Rios de Souza
authors.initials: LR
authors.lastname: Moreira
authors.affiliation: Laboratory of Biophysics, Department of Cellular Biology, University of Brasília, Brasília 70910-900, DF, Brazil. Electronic address: pharmalice@gmail.com.
authors.forename: Alice da Cunha Morales
authors.initials: Ada C
authors.lastname: Álvares
authors.affiliation: Laboratory of Chemistry, Cellulose and Energy, Department of Forest Sciences, ESALQ, University of São Paulo, Piracicaba 13418-220, SP, Brazil. Electronic address: fjrgomes@terra.com.br.
authors.forename: Francides Gomes
authors.initials: FG
authors.lastname: da Silva
authors.affiliation: Laboratory of Biophysics, Department of Cellular Biology, University of Brasília, Brasília 70910-900, DF, Brazil. Electronic address: nina@unb.br.
authors.forename: Sonia Maria
authors.initials: SM
authors.lastname: de Freitas
authors.affiliation: Laboratory of Enzymology, Department of Cellular Biology, University of Brasília, Brasília 70910-900, DF, Brazil. Electronic address: eximenes@unb.br.
authors.forename: Edivaldo Ximenes
authors.initials: EX
authors.lastname: Ferreira Filho
mesh_terms: D001230:Aspergillus / Q000201:enzymology*; D002482:Cellulose / Q000378:metabolism*; D055598:Chemical Phenomena; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry* / Q000378:metabolism*; D006868:Hydrolysis; D010636:Phenols / Q000378:metabolism; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D014990:Xylans / Q000378:metabolism*
chemical_list: D010636:Phenols; D014990:Xylans; D002482:Cellulose; D043364:Endo-1,4-beta Xylanases
keywords: 3,5-Dinitrosalicylic acid (PubChem CID:11873); Acrylamide (PubChem CID: 6579); Cellulose pulp; Cesium chloride (PubChem CID: 24293); Fluorescence spectroscopy; Hydrolysis; Orcinol (PubChem CID: 10436); Phenolic compounds; Potassium iodide (PubChem CID: 4875); Sodium acetate (PubChem CID: 517045); Sodium hydroxide (PubChem CID: 14798); Vanillin (PubChem CID: 1183); Xylanases; Xylose (PubChem CID: 644160); p-Coumaric acid (PubChem CID: 637542)