Structural simulation and protein engineering to convert an endo-chitosanase to an exo-chitosanase.
To obtain an enzyme for the production of chito-disaccharides (GlcN(2)) by converting endo-chitosanase to exo-chitosanase, we chose an endo-chitosanase from Bacillus circulans MH-K1 (Csn) as the candidate for protein engineering. Using molecular modeling, two peptides with five amino acids (PCLGG) and six amino acids (SRTCKP) were designed and inserted after the positions of D(115) and T(222) of Csn, respectively. The inserted fragments are expected to form loops that might protrude from opposite walls of the substrate-binding cleft, thus forming a 'roof' over the catalytic site that might alter the product specificity. The chimeric chitosanase (Chim-Csn) and wild-type chitosanase (WT-Csn) were both over-expressed in Escherichia coli and purified nearly to homogeneity. The products formed from chitosan were analyzed by ESI-MS (electrospray ionization-mass spectrometry). A mixture of GlcN(2), GlcN(3) and GlcN(4) was obtained with WT-Csn, whereas Chim-Csn formed, with a smaller catalytic rate (3% of WT-Csn activity), GlcN(2) as the dominant product. Measurements of viscosity showed that, with similar amounts of enzyme activity, Chim-Csn catalyzed the hydrolysis of chitosan with a smaller rate of viscosity decrease than WT-Csn. The results indicate that, on inserting two surface loops, the endo-type chitosanase was converted into an exo-type chitosanase, which to our knowledge is the first chitosanase that releases GlcN(2) from chitosan as the dominant product.
Yao
Yueh-Yun
YY
Department of Applied Chemistry, National Chiao Tung University, 1001 Ta-Hseh Road, Hsinchu, Taiwan.
Shrestha
Keshab Lal
KL
Wu
Yue-Jin
YJ
Tasi
Huei-Ju
HJ
Chen
Chun-Chen
CC
Yang
Jinn-Moon
JM
Ando
Akikazu
A
Cheng
Chih-Yu
CY
Li
Yaw-Kuen
YK
D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002384:Catalysis; D048271:Chitosan / Q000378:metabolism*; D003198:Computer Simulation; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D006026:Glycoside Hydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006868:Hydrolysis; D008969:Molecular Sequence Data; D015202:Protein Engineering / Q000379:methods; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D021241:Spectrometry, Mass, Electrospray Ionization; D013379:Substrate Specificity
D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; D048271:Chitosan; D006026:Glycoside Hydrolases; C019868:chitosanase