Cationic amphiphilic peptides (CAPs) are usually classified as bacterial membrane targeting molecules. Rational design and modification of cationic and amphiphilic properties of CAPs have made them to be used in new medical and biotechnological applications. However, CAPs modification and development strategies are challenging issues due to the risk of cytotoxicity or hemolytic activity. In this research, modified variants of S3 peptide were introduced. S3 is a linear 34 amino acid peptide derived from the lipopolysaccharide (LPS) binding site of factor C in horseshoe crab’s hemolymph. Net positive charges of variants (S3E3 and S3E3A) increased by either eliminating negatively charged residues of the peptides or substituting them with alanine. Different biological activities of new variants including LPS binding affinity, antimicrobial activity, cytotoxicity against human breast tumor cell line, and hemolytic property were studied and compared to those of S3 peptide. S3E3 variant showed 68.5% higher LPS binding affinity, 40.4% stronger anti-microbial activity, conserved hemolytic property with the same anti-cancer activity compared to S3peptide. These results revealed that elimination/substitution of negatively charged residues will be a proper strategy for modification of S3 peptide.

阳离子两亲性肽（CAPs）通常被分类为细菌膜靶向分子。CAP的阳离子和两亲性质的合理设计和改进使其可以用于新的医学和生物技术应用中。然而，由于细胞毒性或溶血活性的风险，CAPs修饰和开发策略是具有挑战性的问题。在这项研究中，介绍了S3肽的修饰变体。S3是一个线性的34个氨基酸的肽，衍生自horse蟹血淋巴中C因子的脂多糖（LPS）结合位点。变异体（S3E3和S3E3A）的净正电荷通过消除肽的带负电荷的残基或用丙氨酸代替而增加。新变体的不同生物学活性包括LPS结合亲和力，抗菌活性，研究了对人乳腺肿瘤细胞系的细胞毒性和溶血特性，并将其与S3肽进行了比较。与S3肽相比，S3E3变体表现出68.5％的LPS结合亲和力高，40.4％的抗微生物活性强，具有相同抗癌活性的保守溶血性。这些结果表明消除/取代带负电荷的残基将是修饰S3肽的适当策略。