Xylanase II from an alkaliphilic thermophilic Bacillus with a distinctly different structure from other xylanases: Evolutionary relationship to alkaliphilic xylanases

A 1.0 kilobase gene fragment from the genomic DNA of an alkaliphilic thermo philic Bacillus was found to code for a functional xylanase (XynII). The co mplete nucleotide sequence including the structural gene and the 5' and 3' flanking sequences of the xylanase gene have been determined. An open readi ng frame starting from ATG initiator codon comprising 402 nucleotides gave a preprotein of 133 amino acids of calculated molecular mass 14.090 kDa. Th e occurrence of three potential N-glycosylation shes in XynII gene is a uni que feature for a gene of bacterial origin. The stop codon was followed by hairpin loop structures indicating the presence of transcription terminatio n signals. The secondary structure analysis of XynII predicted that the pol ypeptide was primarily formed of p-sheets. XyaII appeared to be a member of family G/11 of xylanases based on its molecular weight and basic pr (8.0), However, sequence homology revealed similar identity with families 10 and 11 of xylanases. The conserved triad (Val-Val-Xaa, where Xaa is Asn or Asp) was identified only in the xylanases from alkaliphilic organisms. Our resu lts implicate for the first; time the concept of convergent evolution for X ynII and provide a basis for research in evolutionary relationship among th e xylanases from alkaliphilic and neutrophilic organisms. (C) 1999 Academic Press.