Modulation of the regioselectivity of a Thermotoga neapolitana beta-glucosidase by site-directed mutagenesis.
Thermotoga neapolitana beta-glucosidase (BglA) was subjected to site-directed mutagenesis in an effort to increase its ability to synthesize arbutin derivatives by transglycosylation. The transglycosylation reaction of the wild-type enzyme displays major beta(1,6) and minor beta(1,3) or beta(1,4) regioselectivity. The three mutants, N291T, F412S, and N291T/F412S, increased the ratio of transglycosylation/hydrolysis compared with the wild-type enzyme when pNPG and arbutin were used as a substrate and an acceptor, respectively. N291T and N219T/F412s had transglycosylation/hydrolysis ratios about 3- and 8-fold higher, respectively, than that of the wild-type enzyme. This is due to the decreased hydrolytic activity of the mutant rather than increased transglycosylation activity. Interestingly, N291T showed altered regioselectivity, as well as increased transglycosylation products. TLC analysis of the transglycosylation products indicated that N291T retained its beta(1,3) regioselectivity, but lost its beta(1,4) and beta(1,6) regioselectivity. The altered regioselectivity of N291T using two other acceptors, esculin and salicin, was also confirmed by TLC. The major transglycosylation products of the wild type and N291T mutant were clearly different. This result suggests that Asn-291 is highly involved in the catalytic mechanism by controlling the transglycosylation reaction.
Choi
Ki-Won
KW
Department of Microbiology, College of Natural Sciences, Pusan National University, Busan 609-735, Korea.
Park
Kyung-Min
KM
Jun
So-Young
SY
Park
Cheon-Seok
CS
Park
Kwan-Hwa
KH
Cha
Jaeho
J
D001104:Arbutin / Q000096:biosynthesis*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D019020:Directed Molecular Evolution; D016297:Mutagenesis, Site-Directed; D015202:Protein Engineering; D013379:Substrate Specificity; D046949:Thermotoga neapolitana / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D001617:beta-Glucosidase / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism
D001426:Bacterial Proteins; D001104:Arbutin; D001617:beta-Glucosidase