Preparation, structure and activity determinations of novel immunomodulatory peptides from Limnospira platensis

Immunomodulatory peptides derived from food proteins have attracted worldwide attention. In this study, phycocyanin-derived peptides from Limnospira platensis were prepared using enzymatic hydrolysis with commercial proteases and ultrafiltration, and investigated their immunomodulatory activity on RAW264.7 cells. The results showed that papain hydrolysate ultrafiltration with molecular weight of <3 kDa (named PP) could promote the cell viability of RAW264.7. Subsequently, a series of peptides was determined from PP using UPLC-MS/MS, and their toxicity and activities were predicted through PeptideRanker analysis. Six novel peptides with high potential immunomodulatory activity, FGRFR, SPSWY, YNKFPY, GYYLRM, MFDAF, and MAACLR, were screened to be synthesized chemically and assessed their immunomodulatory activities on RAW264.7. Experimental results demonstrated these six novel synthetic peptides could increase immune function and cytokine secretion of RAW264.7 cells. Meanwhile, they also showed stability after simulated gastrointestinal digestion and treatment at different temperatures and pH levels. Moreover, molecular-docking assays indicated their immunomodulatory activities were related to the interaction between peptides and TLRs receptors. These phycocyanin hydrolysate and novel immunomodulatory peptides from Limnospira platensis have potential applications in functional foods and medicine.