Molecular orbital theory on cellulolytic reactivity between pNP-cellooligosccharides and beta-glucosidase from Cellulomonas uda CS1-1.
A beta-glucosidase with the molecular mass of 160,000 Da was purified to homogeneity from cell extract of a cellulolytic bacterium, Cellulomonas uda CS1-1. The kinetic parameters (Km and Vmax) of the enzyme were determined with pNP-cellooligosccharides (DP 1-5) and cellobiose. The molecular orbital theoretical studies on the cellulolytic reactivity between the pNP-cellooligosaccharides as substrate (S) molecules and the purified beta-glucosidase (E) were conducted by applying the frontier molecular orbital (FMO) interaction theory. The results of the FMO interaction between E and S molecules verified that the first stage of the reaction was induced by exocyclic cleavage, which occurred in an electrophilic reaction based on a strong charge-controlled reaction between the highest occupied molecular orbital (HOMO) energy of the S molecule and the lowest occupied molecular orbital (LUMO) energy of the hydronium ion (H3O+), more than endocyclic cleavage, whereas a nucleophilic substitution reaction was induced by an orbital-controlled reaction between the LUMO energy of the oxonium ion (SH+) protonated to the S molecule and the HOMO energy of the H2O2 molecule. A hypothetic reaction route was proposed with the experimental results in which the enzymatic acid-catalyst hydrolysis reaction of E and S molecules would be progressed via SN1 and SN2 reactions. In addition, the quantitative structure-activity relationships (QSARs) between these kinetic parameters showed that Km has a significant correlation with hydrophobicity (logP), and specific activity has with dipole moment, respectively.
Yoon
Min-Ho
MH
Division of Applied Biology and Chemistry, College of Agriculture and Life Sciences, Chungnam National University, Daejeon 305-764, Korea.
Nam
Yun-Kyu
YK
Choi
Woo-Young
WY
Sung
Nack-Do
ND
D040143:Cellulomonas / Q000201:enzymology*; D002482:Cellulose / Q000378:metabolism*; D006868:Hydrolysis; D007700:Kinetics; D009844:Oligosaccharides / Q000737:chemistry*; D021281:Quantitative Structure-Activity Relationship; D001617:beta-Glucosidase / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
D009844:Oligosaccharides; D002482:Cellulose; D001617:beta-Glucosidase