Journal
BIOTECHNOLOGY AND BIOPROCESS ENGINEERING
Volume 18, Issue 1, Pages 35-42Publisher
KOREAN SOC BIOTECHNOLOGY & BIOENGINEERING
DOI: 10.1007/s12257-012-0455-x
Keywords
Bacillus circulans xylanase; arginine; pH optimum; acidic side; activity
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Funding
- National Research Foundation of Korea
- Korean Government (MEST) [NRF-2011-C1AAA001-2011-0030345]
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Electrostatic interactions are important in protein folding, binding, flexibility, stability and function. The pH at which the enzyme is maximally active is determined by the pK(a)s of the active site residues, which are modulated by several factors including the change in electrostatics in its vicinity. As the acidic xylanases are important in food and animal feed industries, electrostatic interactions are introduced in Bacillus circulans xylanase to shift their pH optima towards the acidic side. Arg substitutions are made to modulate the pKas of the active site residues. Neutral residues are substituted by Arg in such a way that the substituted residue can make direct interaction with the catalytic residues. However, the mutations with other titratable residues (Asp, Arg, Lys, His, Tyr, and Ser) present in between the catalytic sites and the substituted sites are avoided. Site directed mutagenesis was conducted to confirm the strategy. The results show the shift in pH optima of the mutants towards the acidic side by 0.5-1.5 unit. Molecular dynamics simulation of the mutant V37R reveals that the decrease in activity is due to the increase in distance between the substrate oxygen atoms and catalytic glutamates.
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