We purified an ˜6.4-kDa antimicrobial peptide from an acidified gill extract of the Pacific oyster, Crassostrea gigas, by cation-exchange and C18 reversed-phase high performance liquid chromatography (HPLC). The identified peptide was composed of 54 amino acids and had a molecular weight of 6484.6 Da. Comparison of the amino acid sequence and molecular weight with those of other known proteins or peptides revealed that the peptide had high identity with the 60S ribosomal protein L29, and so was named cgRPL29.
The full-length cgRPL29 cDNA of the Pacific oyster comprised 325-bp, including a 5’-untranslated region (UTR) of 100-bp, a 3′-UTR of 57-bp, and an open reading frame of 168-bp encoding 55 amino acids, with a Met residue at the N-terminus. The cgRPL29 mRNA tissue distribution suggested that it is constitutively expressed in a non-tissue-specific manner. Secondary structural prediction and homology modeling indicated cgRPL29 have an unordered structure containing two partial α-helical regions. This is to our knowledge the first report of the antimicrobial effect of the 60S ribosomal protein L29 from marine invertebrates.