[Expression of N domain of chromogranin A in Bacillus subtilis and its antifungal activity]

Chromogranin A (CGA) is a soluble protein existed in most secreted cells and neurons. It was recently found that the bovine CGA N terminal region has vasoinhibitory, antibacterial and antifungal activities. Since the need for effective antifungal agents increases in parallel with the expanding number of immunocompromised patients at risk for fungal infections, it becomes imperative to find antifungal compounds with low toxicity toward mammalian cells. To study the antifungal activity of CGA N terminal region, the DNA fragment encoding for the N terminal 1-76 amino acid sequence (CGA1-76) of human CGA was amplified by PCR technique. After DNA sequence analysis, the amplified DNA fragment was cloned into the Bacillus subtilis inducible and expression vector pSBPTQ constructed in this study and the resultant plasmid pSVTQ was then transformed into triple-protease deficient Bacillus subtilis strain DB403 competent cells. The transformants was screened on LB plates containing 10 microg/mL kanamycin. The positive transformant DB403 (pSVTQ) was grown on kanmycin containing 2 x MSR medium and sucrose was added to 2% final concentration for induction after 2h cultivation. The culture supernatant was used to run SDS-PAGE. The result of SDS-PAGE showed that the CGA1-76 was expressed by sucrose induction and the expressed product secreted into the medium with a yield of 5 mg/L. The expressed product reacts specifically with mouse anti CGA47-68 monoclonal antibody. The antifungal activity of the expressed product was examined by adding the culture supernatant to the fungal spore or Candida albican suspensions at appropriate proportion and found that the recombinant human CGA1-76 produced in Bacillus subtilis inhibits the growth of Fusarium sp. Alternaria sp. and Candida albican at the concerntration of 4 micromol/L. These results demonstrate that human CGA1-76 has expressed in Bacillus subtilis and the expressed product is immunogenic and has the antifungal activity.