Identification and molecular modeling of a family 5 endocelluase from Thermus caldophilus GK24, a cellulolytic strain of Thermus thermophilus

Abstract

The genome of T. caldophilus GK24 was recently sequenced and annotated as 14 contigs, equivalent to 2.3 mega basepairs (Mbp) of DNA. In the current study, we identified a unique 13.7 kbp DNA sequence, which included the endocellulase gene of T. caldophilus GK24, which did not appear to be present in the complete genomic sequence of the closely related species T. thermophilus HB27 and HB8. Congo-red staining revealed a unique phenotype of cellulose degradation by strain GK24 that was distinct from other closely related Thermus strains. The results showed that strain GK24 is an aerobic, thermophilic, cellulolytic eubacterium which belongs to the group T. thermophilus. In order to understand the mechanism of production of cellobiose in T. caldophilus GK24, a three-dimensional model of the endocellulase, TcCel5A, was generated based on known crystal structures. Using this model, we carried out a flexible cellotetraose docking study.