Molecular cloning, heterologous expression, and in silico sequence analysis of Enterobacter GH19 class I chitinase (chiRAM gene)

Background Using in silico sequence analyses, the present study aims to clone and express the gene-encoding sequence of a GH19 chitinase from Enterobacter sp. in Escherichia coli. Methods and results The putative open reading frame of a GH19 chitinase from Enterobacter sp. strain EGY1 was cloned and expressed into pGEM (R)-T and pET-28a (+) vectors, respectively using a degenerate primer. The isolated nucleotide sequence (1821 bp, GenBank accession no.: MK533791.2) was translated to a chiRAM protein (606 amino acids, UniProt accession no.: A0A4D6J2L9). The in silico protein sequence analysis of chiRAM revealed a class I GH19 chitinase: an N-terminus signal peptide (Met(1)-Ala(23)), a catalytic domain (Val(83)-Glu(347) and the catalytic triad Glu(149), Glu(171), and Ser(218)), a proline-rich hinge region (Pro(414)-Pro(450)), a polycystic kidney disease protein motif (Gly(465)-Ser(533)), a C-terminus chitin-binding domain (Ala(553)-Glu(593)), and conserved class I motifs (NYNY and AQETGG). A three-dimensional model was constructed by LOMETS MODELLER of PDB template: 2dkvA (class I chitinase of Oryza sativa L. japonica). Recombinant chiRAM was overexpressed as inclusion bodies (IBs) (similar to 72 kDa; SDS-PAGE) in 1.0 mM IPTG induced E. coli BL21 (DE3) Rosetta strain at room temperature 18 h after induction. Optimized expression yielded active chiRAM with 1.974 +/- 0.0002 U/mL, on shrimp colloidal chitin (SCC), in induced E. coli BL21 (DE3) Rosetta cells growing in SB medium. LC-MS/MS identified a band of 72 kDa in the soluble fraction with a 52.3% coverage sequence exclusive to the GH19 chitinase of Enterobacter cloacae (WP_063869339.1). Conclusions Although chiRAM of Enterobacter sp. was successfully cloned and expressed in E. coli with appreciable chitinase activity, future studies should focus on minimizing IBs to facilitate chiRAM purification and characterization.