[Cloning, expression and biochemical characterization of a novel diacetylchitobiose deacetylase from the hyperthermophilic archaeon Pyrococcus horikoshii].

Chitin is the second most abundant organic compound in nature and the degradation of this biomass is an important process in the recycling of nutrients in the environments. Several biodegradation pathway of chitin have been classified in eukaryotes and bacteria, and a unique chitin degradation pathway was proposed according to recent studies on hyperthermophilic archaeon Thermococcus kodakaraensis. In the genome of Pyrococcus horikoshii, several ORFs show high homology to the chitin-degrading related genes from T. kodakararaensis, therefore P. horikoshii is likely to have the same chitin degrading pathway as that of T. kodakaraensis. In order to further characterize the novel chitin degrading pathway in thermophilic archaea, a diacetylchitobiose deacetylase from P. horikoshii (Dacph) was studied in the present study. Dacph belongs to the LmbE-like protein family and the amino sequence is not related to the other deacetylases studied before (except that in T. kodakararaensis). The gene (Dacph, PH0499) from the hyperthermophilic archaeon P. horikoshii was amplified by polymerase chain reaction, cloned into expression vector pET15b, and expressed in E. coli BL21-codonPlus (DE3)-RIL. A soluble fraction of Dacph (31.6kDa) was obtained as shown by SDS-PAGE. TLC analysis showed that Dacph is able to deacetylate one acetyl group of GlcNAc2 and GlcNAc. By the concerted reaction with the Exo-beta-D-Glucosaminid-ase (BglAph), it is also able to convert GlcNAc2 into GlcN. It is concluded that PH0499 is a diacetylchit-obiose deacetylase. By reaction together with Exo-beta-D-Glucosaminidase in P. horikoshii, Dacph probably plays a key role in the new chitin degradation pathway in hyperthermophilic archaea (the genera Thermococcus and Pyrococcus).