Cloning and bioinformatics analysis of an endoglucanase gene (Aucel12A) from Aspergillus usamii and its functional expression in Pichia pastoris

Using 3′ and 5′ rapid amplification of cDNA ends methods, the full-length cDNA sequence encoding an endo-1,4-β-glucanase of Aspergillus usamii E001 (abbreviated as AuCel12A) was amplified from the total RNA. The clone cDNA sequence of the gene encoding the AuCel12A, named as Aucel12A, is 1,027 bp in length harboring 5′ and 3′ non-coding regions, as well as a 720 bp of open reading frame that encodes a 16-aa signal peptide, and a 223-aa mature AuCel12A with a theoretical M.W. of 24,294 Da, a calculated pI of 4.15, and one putative N-glycosylation site. The complete DNA sequence of the gene Aucel12A was amplified from the genomic DNA of A. usamii E001 by using the conventional PCR and pUCm-T vector-mediated PCR initially developed in our lab. The clone DNA sequence is 1,576 bp in length, consisting of a 5′ flanking regulatory region, three exons, and two introns with sizes of 50 and 66 bp. The cDNA fragment encoding the mature AuCel12A was expressed in a fully active form in Pichia pastoris. One P. pastoris transformant expressing the highest recombinant AuCel12A (rAuCel12A) activity, labeled as P. pastoris GSCel2-1, was chosen for subsequent studies. Integration of the Aucel12A into P. pastoris genome was confirmed by PCR analysis using 5′- and 3′-AOX1 primers. SDS-PAGE and enzyme activity assays demonstrated that the rAuCel12A, a glycosylated protein with an apparent M.W. of 27.0 kDa and a carbohydrate content of 4.82%, was secreted into the culture medium. The purified rAuCel12A displayed the highest activity at pH 5.0 and 60°C. It was highly stable at a pH range of 3.5–7.0, and at a temperature of 55°C or below. Its activity was not significantly affected by an array of metal ions and EDTA, but inhibited by Ag⁺, Hg²⁺ and Fe²⁺. The K _m and V _max of the rAuCel12A, towards carboxymethylcellulose-Na (CMC-Na) at pH 5.0 and 50°C were 4.85 mg/ml and 160.5 U/mg, respectively.