Aquatic freshwater fish like catfish, Silurus asotus, lives in microbe-rich environments, which enable this fish to develop necessary defense mechanisms. Antimicrobial peptides, along with other innate immune factors, are regarded as an important group in this defense. An antimicrobial peptide, which was isolated from the skin of S. asotus, was identified as a C-terminal fragment of 60S ribosomal protein L27 from S. asotus. The peptide was, then, designated Silurus asotus 60S ribosomal protein L27-derived antimicrobial peptide, SaRpAMP. Primary structure analyses and cDNA cloning revealed that SaRpAMP was 4185.36 Da and composed of 33 amino acids (AAs). Its precursor had a total of 136 AAs containing a pro-sequence of 103 AAs encoded by the nucleotide sequence of 512 bp that comprises a 5′ untranslated region (UTR) of 32 bp, an open reading frame (ORF) of 411 bp, and a 3′ UTR of 69 bp. Secondary structure analyses showed that SaRpAMP had two α-helices with turns and coils and an amphiphilic structure, a finding consistent with the 3D model of the peptide. SaRpAMP exhibited potent antibacterial activity comparable to piscidin 1, a powerful positive control. Its antimicrobial activity against fungus C. albicans was relatively weak. The antimicrobial activity of SaRpAMP was not diminished by heat treatment and changes in pH but was abolished by proteolytic enzyme digestion. Membrane permeability assays suggested that SaRpAMP interacts with both the outer and inner bacterial membranes. This was consistent with the results of lipid titration and quenching of Trp fluorescence that demonstrated SaRpAMP's interaction with acidic liposomes. Collectively, these findings suggest that the identified peptide, SaRpAMP, was the first antimicrobial peptide reported to be derived from the C-terminal region of 60S ribosomal protein L27. The findings also suggest that the action mechanism of SaRpAMP involved the interaction of the peptide with the bacterial membranes.

水生淡水鱼（如cat鱼，灰Sil（Silurus asotus））生活在富含微生物的环境中，这使该鱼能够发展必要的防御机制。抗菌肽和其他先天免疫因子一起被认为是这种防御的重要组成部分。从沙门氏菌的皮肤分离出的抗菌肽被鉴定为来自沙门氏菌的60S核糖体蛋白L27的C端片段。然后，将该肽命名为Silurus asotus 60S核糖体蛋白L27衍生的抗菌肽Sa RpAMP。一级结构分析和cDNA克隆显示SaRpAMP为4185.36 Da，由33个氨基酸（AAs）组成。其前体总共有136个AA，其中包含103个AA的前序序列，该序列由512 bp的核苷酸序列编码，该序列包含32 bp的5'非翻译区（UTR），411 bp的开放阅读框（ORF），以及69 bp的3'UTR。二级结构分析表明，Sa RpAMP具有两个带有匝和线圈的α螺旋，并且具有两亲结构，这一发现与该肽的3D模型相符。Sa RpAMP表现出与强大的阳性对照piscidin 1相当的有效抗菌活性。其对真菌白色念珠菌的抗菌活性相对较弱。Sa的抗菌活性RpAMP不会因热处理和pH值的变化而降低，但会因蛋白水解酶的消化而消失。膜通透性测定表明，Sa RpAMP与细菌内外膜相互作用。这与脂质滴定和Trp荧光淬灭的结果一致，该结果表明Sa RpAMP与酸性脂质体的相互作用。总体而言，这些发现表明，鉴定出的肽Sa RpAMP是第一个据报道源自60S核糖体蛋白L27 C端区域的抗菌肽。这些发现还表明Sa RpAMP的作用机制涉及该肽与细菌膜的相互作用。