TY - JOUR
T1 - Substrate specificity in glycoside hydrolase family 10 - Tyrosine 87 and Leucine 314 play a pivotal, role in discriminating between glucose and xylose binding in the proximal active site of pseudomonas cellulosa xylanase 10A
AU - Andrews, S R
AU - Charnock, S J
AU - Lakey, J H
AU - Davies, G J
AU - Claeyssens, M
AU - Nerinckx, W
AU - Underwood, M
AU - Sinnott, M L
AU - Warren, R A J
AU - Gilbert, H J
PY - 2000/7/28
Y1 - 2000/7/28
N2 - The Pseudomonas family 10 xylanase, Xyl10A, hydrolyzes beta 1,4-linked xylans but exhibits very low activity against aryl-beta-cellobiosides. The family 10 enzyme, Cex, from Cellulomonas fimi, hydrolyzes aryl-beta-cellobiosides more efficiently than does Xyl10A, and the movements of two residues in the -1 and -2 subsites are implicated in this relaxed substrate specificity (Notenboom, V., Birsan, C., Warren, R. A. J., Withers, S. G., and Rose, D. R. (1998) Biochemistry 37, 4751-4758). The three-dimensional structure of Xyl10A suggests that Tyr-87 reduces the affinity of the enzyme for glucose-derived substrates by steric hindrance with the C6-OH in the -2 subsite of the enzyme. Furthermore, Leu-314 impedes the movement of Trp-313 that is necessary to accommodate glucose-derived substrates in the -1 subsite. We have evaluated the catalytic activities of the mutants Y87A, Y87F, L314A, L314A/Y87F, and W313A of Xyl10A. Mutations to Tyr-87 increased and decreased the catalytic efficiency against 4-nitrophenyl-beta-cellobioside and 4-nitrophenyl-beta-xylobioside, respectively The L314A mutation caused a 200-fold decrease in 4-nitrophenyl-beta-xylobioside activity but did not significantly reduce 4-nitrophenyl-beta-cellobioside hydrolysis. The mutation L314A/Y87A gave a 6500-fold improvement in the hydrolysis of glucose-derived substrates compared with xylose-derived equivalents. These data show that substantial improvements in the ability of Xyl10A to accommodate the C6-OH of glucose-derived substrates are achieved when steric hindrance is removed.
AB - The Pseudomonas family 10 xylanase, Xyl10A, hydrolyzes beta 1,4-linked xylans but exhibits very low activity against aryl-beta-cellobiosides. The family 10 enzyme, Cex, from Cellulomonas fimi, hydrolyzes aryl-beta-cellobiosides more efficiently than does Xyl10A, and the movements of two residues in the -1 and -2 subsites are implicated in this relaxed substrate specificity (Notenboom, V., Birsan, C., Warren, R. A. J., Withers, S. G., and Rose, D. R. (1998) Biochemistry 37, 4751-4758). The three-dimensional structure of Xyl10A suggests that Tyr-87 reduces the affinity of the enzyme for glucose-derived substrates by steric hindrance with the C6-OH in the -2 subsite of the enzyme. Furthermore, Leu-314 impedes the movement of Trp-313 that is necessary to accommodate glucose-derived substrates in the -1 subsite. We have evaluated the catalytic activities of the mutants Y87A, Y87F, L314A, L314A/Y87F, and W313A of Xyl10A. Mutations to Tyr-87 increased and decreased the catalytic efficiency against 4-nitrophenyl-beta-cellobioside and 4-nitrophenyl-beta-xylobioside, respectively The L314A mutation caused a 200-fold decrease in 4-nitrophenyl-beta-xylobioside activity but did not significantly reduce 4-nitrophenyl-beta-cellobioside hydrolysis. The mutation L314A/Y87A gave a 6500-fold improvement in the hydrolysis of glucose-derived substrates compared with xylose-derived equivalents. These data show that substantial improvements in the ability of Xyl10A to accommodate the C6-OH of glucose-derived substrates are achieved when steric hindrance is removed.
KW - FLUORESCENS SUBSPECIES CELLULOSA
KW - BETA-1,4-GLYCANASE CEX
KW - DIRECTED MUTAGENESIS
KW - CRYSTAL-STRUCTURE
KW - SEQUENCE
KW - ENZYME
KW - FIMI
KW - INTERMEDIATE
KW - EXPRESSION
KW - PROTEIN
M3 - Article
SN - 0021-9258
VL - 275
SP - 23027
EP - 23033
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 30
ER -