Preliminary analysis of cellulose and action model of three endoglucanases from Xanthomonas axonopodis pv. citri

【Objeetive】Citrus bacterial canker(CBC) disease caused by Xanthomonas axonopodis pv. citri is one of most serious quarantine diseases in citrus production. It is speculated that Xac cellulase play a part in invading the host and is the necessary pathogenic factor.【Methods】To get the information of the isoelectric point,molecular weight,signal peptide,domains and functions of Xac cellulase,bioinformatic analysis of Xac cellulases was used. Typical cellulases such as Xaccel1,Xaccel3 and Xaccel5 were cloned and expressed in vector of p ET28a(+) and the activity of the three cellulases were dectected.【Results】Xac family has 22 cellulases. According to their homology,structure characteristics and functional structure domain predicted on line,these cellulases can be divided into 11 groups by Clustal X1.83. The length of the Xac cellulase is about 350 aa,63.6% has signal peptide. Xac cellulase has Glycoside Hydrolase Family 5,Glycoside Hydrolase Family 8,Glycoside Hydrolase Family 9 and Glycoside Hydrolase Family 12 activity sites. 54.5% of the Xac cellulase have GH5 module which is the main module of the Xac cellulase. In addition,there are Cel D_N,CBM,TAT domains and other functional modules such asSCOP and PDB. Xac cellulase has homologous protein with Xanthomonas cellulase. Xac cellulase has thehighest homology with Xcv cellulose on the types and numbers of the functional domains. Xaccel1 can degrade CMC,Avicel,Barley β-glucan,and xylan. Xaccel3 can degrade CMC,Avicel and xylan. Xaccel5 can degrade xylan and Avicel. Three enzymes cannot degrade laminarin and PASC. By degrading the chosen five p NP synthetic substrates,Xaccel1 and Xaccel3 should be endo-glucanases which could breakage the β-1,4 glycosidic bond and degrading glucose. The endo-glucanase of Xaccel5 is not confirmed,needing further studied. 【Conclution】Xaccel1(with GH12) and Xaccel3(with GH5 and CBM2) should be endo-glucanase which exploit many kinds of saccharine by freely breaking the β-1, 4 glycosidic bond and degrading corresponding glucose. The endo-glucanase of Xaccel5(with GH5) only acts on β-1, 4 glycosidic bonds from the substrate reducing end.