title: Structural Insight into and Mutational Analysis of Family 11 Xylanases: Implications for Mechanisms of Higher pH Catalytic Adaptation.
abstract: To understand the molecular basis of higher pH catalytic adaptation of family 11 xylanases, we compared the structures of alkaline, neutral, and acidic active xylanases and analyzed mutants of xylanase Xyn11A-LC from alkalophilic Bacillus sp. SN5. It was revealed that alkaline active xylanases have increased charged residue content, an increased ratio of negatively to positively charged residues, and decreased Ser, Thr, and Tyr residue content relative to non-alkaline active counterparts. Between strands β6 and β7, alkaline xylanases substitute an α-helix for a coil or turn found in their non-alkaline counterparts. Compared with non-alkaline xylanases, alkaline active enzymes have an inserted stretch of seven amino acids rich in charged residues, which may be beneficial for xylanase function in alkaline conditions. Positively charged residues on the molecular surface and ionic bonds may play important roles in higher pH catalytic adaptation of family 11 xylanases. By structure comparison, sequence alignment and mutational analysis, six amino acids (Glu16, Trp18, Asn44, Leu46, Arg48, and Ser187, numbering based on Xyn11A-LC) adjacent to the acid/base catalyst were found to be responsible for xylanase function in higher pH conditions. Our results will contribute to understanding the molecular mechanisms of higher pH catalytic adaptation in family 11 xylanases and engineering xylanases to suit industrial applications.
authors.affiliation: National Engineering Laboratory for Industrial Enzymes, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China; National Engineering Laboratory for Industrial Enzymes, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China; School of Life Science, Shanxi Normal University, Linfen, 041004, China.
authors.forename: Wenqin
authors.initials: W
authors.lastname: Bai
authors.affiliation: National Engineering Laboratory for Industrial Enzymes, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Zhou
authors.affiliation: Institute of Agro-Products Processing Science and Technology, Chinese Academy of Agriculture Sciences, Beijing, 100193, China.
authors.forename: Yueju
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: National Engineering Laboratory for Industrial Enzymes, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China.
authors.forename: Qinhong
authors.initials: Q
authors.lastname: Wang
authors.affiliation: National Engineering Laboratory for Industrial Enzymes, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences, Tianjin, 300308, China; National Engineering Laboratory for Industrial Enzymes, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.
authors.forename: Yanhe
authors.initials: Y
authors.lastname: Ma
mesh_terms: D000222:Adaptation, Physiological; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000378:metabolism; D001407:Bacillus / Q000201:enzymology*; D055162:Biocatalysis; D020134:Catalytic Domain; D004252:DNA Mutational Analysis; D043364:Endo-1,4-beta Xylanases / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D008969:Molecular Sequence Data; D005810:Multigene Family; D050505:Mutant Proteins / Q000737:chemistry; D010802:Phylogeny; D017433:Protein Structure, Secondary; D016415:Sequence Alignment; D012997:Solvents
chemical_list: D000596:Amino Acids; D050505:Mutant Proteins; D012997:Solvents; D043364:Endo-1,4-beta Xylanases