Secretory Expression of Recombinant Human Calcitonin in Green Microalgae Chlamydomonas reinhardtii

Calcitonin is a small peptide hormone that is produced by parafollicular thyroid cells in human and regulates the metabolism of calcium and phosphorus. It is therapeutically used in treatment of calcium-related disorders and osteoporosis. Recombinant calcitonin production encounters with several difficulties due to instability and low molecular weight, and also needs further treatment in prokaryotic systems. Microalgae have recently garnered high attention for their potential in expression of recombinant proteins. The aim of present study was to assess the ability of Chlamydomonas Reinhardtii to express recombinant human calcitonin. The optimized calcitonin coding sequence and carbonic anhydrase secretory signal was cloned in Pchlamy _3 and Pchlamy_4 vectors. The recombinant plasmids were transformed to wild type and also a cell wall deficient strain of Chlamydomonas Reinhardtii by electroporation. Transformed strains were screened by colony PCR method and selected strains were cultivated to produce recombinant calcitonin. Culture media have been collected after cells growth and assayed by ELISA method. Pchlamy_3 vector could not express the target sequence as desired and all the recombinant strains were resulted from Pchlamy_4 vector. The wild type strain also did not show desired yield and only cell wall deficient strain was successfully transformed. The yield of recombinant calcitonin produced by positive strain was about 1 pg/ml. The results of this study show that the used strategy for secretory production of recombinant calcitonin was successful and it could be used in further studies.