Cloning, sequences, and characterization of two chitinase genes from the antarctic Arthrobacter sp strain TAD20: Isolation and partial characterization of the enzymes

Arthrobacter sp. strain TAD20, a chitinolytic gram-positive organism, was i solated from the sea bottom along the Antarctic ice shell. Arthrobacter sp. strain TAD20 secretes two major chitinases, ChiA and ChiB (ArChiA and ArCh iB), in response to chitin induction. A single chromosomal DNA fragment con taining the genes coding for both chitinases was cloned in Escherichia coli . DNA sequencing analysis of this fragment revealed two contiguous open rea ding frames coding for the precursors of ArChiA (881 amino acids [aa]) and ArChiB (578 aa). ArChiA and ArChiB are modular enzymes consisting of a glyc osyl-hydrolase family 18 catalytic domain as well as two and one chitin-bin ding domains, respectively. The catalytic domain of ArChiA exhibits 55% ide ntity with a chitodextrinase from Vibro furnissii. The ArChiB catalytic dom ain exhibits 33% identity with chitinase A of Bacillus circulans. The ArChi A chitin-binding domains are homologous to the chitin-binding domain of ArC hiB. ArChiA and ArChiB were purified to homogeneity from the native Arthrob acter strain and partially characterized. Thermal unfolding of ArChiA, ArCh iB, and chitinase A of Serratia marcescens was studied using differential s canning calorimetry. ArChiA and ArChiB, compared to their mesophilic counte rpart, exhibited increased heat lability, similar to other cold-adapted enz ymes.