Cloning, heterologous expression, and characterization of the Erysipelothrix rhusiopathiae DnaK protein

The dnaK (hsp70) gene from the facultative intracellular pathogen Erysipelothrix rhusiopathiae was cloned by heterologous DNA hybridization of a genomic library using the Escherichia coli dnaK gene as a probe. A 3.2-kb fragment which encoded an 1,800-bp open reading frame was recovered. The deduced amino acid sequence of this open reading frame shares 56% identity with the E. coli DnaK protein. Expression of the encoded protein in E. coli by using the phage T7 promoter/polymerase system resulted in accumulation of a unique 65-kDa protein. Western blot (immunoblot) analysis of extracts from a recombinant E. coli strain using anti-E. coli DnaK polyclonal antibodies confirmed that the cloned gene encodes a DnaK homolog. The recombinant E. rhusiopathiae DnaK protein was purified to 80% homogeneity by ATP affinity chromatography. The purified material hydrolyzed ATP with a specific activity of 100 nmol min-1 mg of protein-1. Analysis of total protein extracts from E. rhusiopathiae indicates that DnaK is a highly expressed protein in this organism.