Molecular characterization of a calponin-like protein from Schistosoma japonicum

The gene for a Schistosoma japonicum (Philippine strain origin) (Sjp) calponin-like protein has been cloned and characterised. The clone, designated P14, was isolated from a Sjp adult worm lambda ZAP cDNA library by immunoscreening, and was shown to contain a full-length cDNA encoding a 38.3 kDa protein that shared significant sequence similarity to a number of previously reported calponins and 22 kDa smooth-muscle proteins. Northern analysis indicated the P14 transcript was approximately 2.2 kb in both Sjp and Chinese strain S. japonicum (Sjc) adult worms. Southern blot analysis of genomic DNA suggested that several copies of the P14 gene are present in the Sjc and Sjp genomes but only one copy was evident in the S. mansoni (Sm) genome. Western blot analysis indicated that the product of P14 occurs as a 38 kDa protein in adult Sjp worms and homologues are present in adult worms of Sjc and Sm. At least six isoforms, all with a similar molecular size of approximately 38 kDa and isoelectric points ranging from 8.1 to 9.5, were present in adult Sjc worms. The protein was immunolocalized to the muscle of male and female Sjc adult worms. Recombinant protein was expressed in E. coli and purified under denaturing conditions, and in yeast to produce a soluble protein in purified form. The availability of purified, correctly folded protein will allow investigations into its biological functions and potential involvement in host immunity.