Family 11 endo-β-1,4-xylanases degrade xylan, the main constituent of plant hemicelluloses, and have many potential uses in biotechnology. The structure of Xyl1, a family 11 endo-xylanase from Streptomyces sp. S38, has been solved. The protein crystallized from ammonium sulfate in the trigonal space group P321, with unit-cell parameters a = b = 71.49, c = 130.30 Å, γ = 120.0°. The structure was solved at 2.0 Å by X-ray crystallography using the molecular-replacement method and refined to a final R factor of 18.5% (Rfree = 26.9%). Xyl1 has the overall fold characteristic of family 11 xylanases, with two highly twisted β-sheets defining a long cleft containing the two catalytic residues Glu87 and Glu177.
The alignment of the promoter region of several Streptomyces xylanases shows three conserved sequences which could be involved in gene regulation. By electromobility shift assays these specific sequences, present only in Streptomyces xylanolytic strains, were identified as protein-binding sites. The sequence required for efficient recognition by the retarding protein appeared to be a 4-bp inverted repeat: 5′-CTTT-Nx-AAAG-3′. The DNA-protein affinity was influenced by the culture conditions.
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