Multiple classes of penaeidin antimicrobial peptides expressed in individual shrimp exhibit microbial target specificity and a class specific gain of function in a single domain

Abstract

Penaeidins are unique, two domain antimicrobial peptides (AMP) that target, inhibit the growth of, and kill microbial species. Penaeidins diversity was observed from the expressed gene level to the mature protein level in a single shrimp species, Litopenaeus vannamei. It was determined that three penaeidin classes were expressed simultaneously by hemocytes of individual shrimp from two different species, L. vannamei and L. setiferus. Since, multiple penaeidin classes are present in individual shrimp, the relevance of possessing this array of different peptides all from the same family as part of an individual's immune system was examined. A target specific character was observed for the different penaeidin classes, indicating a partitioning of function within this AMP family, which suggests that the diversity in penaeidins serves an important role in contributing to the breadth of the shrimp immune response. Penaeidins exhibit multiple functions as single, uniform isomers including microbial target specificity and chitin binding, which probably serves a role in surface protection. One of the most striking traits observed across penaeidin classes is the independent antimicrobial activity of the class 4 proline-rich domain (PRD Pen4-1). This contrasts with very little observed analogous function for the class 3 proline-rich domain. The function of penaeidins as components of the shrimp immune system is undoubtedly significant although not yet totally defined. The target specific character of penaeidins in the context of their fungicidal activity led to the discovery that these peptides kill antibiotic resistant human fungal pathogens. Furthermore PRD Pen4-1 exhibits a target specific function against antibiotic resistant steroforms of Cryptococcus neoformans and Candida spp. that is more effective than that of the full-length penaeidin isoforms. This finding defined the PRD as the minimal essential unit of the penaeidin AMP, described thus far, that can be used as an effective and specific antibiotic. This demonstrated that the structurally complex cysteine-rich domain may inhibit effectiveness of the full-length penaeidin against certain microbes. Through examining the phenomenon of AMP functional complexity in individual shrimp, information has been gained that has great potential utility in the context of developing specific antibiotics that can be applied to benefit human health directly.