Investigating the Critical Role of Serine in GL13K Peptide Binding to LPS

This research project aims to mechanistically investigate and quantify the interaction between the synthetic antimicrobial peptide (AMP) GL13K (GKIIKLKASLKLL )[1] and gram-negative bacteria endotoxin ,Lipopolysaccharide (LPS) extracted from Escherichia coli (E. coli) O111:B4 [2], with a specific focus on the critical role of the Serine 9 (Ser09) residue. Purpose The purpose of this project is to investigate the atomic-level mechanism by which the GL13K peptide acts as an anti-sepsis agent by neutralizing bacterial LPS molecule potency outside the bacterial outer membrane (OM). Current literature establishes that GL13K significantly improves the survival of LPS-infected mice[3], but the precise molecular reason for its potent LPS detoxification remains poorly understood. A crucial finding from previous studies suggest that the Serine 9 (Ser09) residue is singularly responsible for GL13K's ability to bind LPS[3]. Additionally, in previous study, we observed that GL13K at pH 10.5 forms a beta-hairpin at c-terminus, exposing the Ser09 at the tip of this structure[4]. This research seeks to move beyond this qualitative observation by quantitatively validating and structurally explaining the Serine 9 dependency, while also exploring a key regulatory mechanism. We describe the goals as: 1. Quantify the Serine 9 role: Precisely calculate and compare the binding affinities of wild-type GL13K and the S9A mutants (Ser-> Ala, Ser-> Thr) to E. coli LPS, proving Ser09 is the molecular anchor. 2. Establish Molecular Causality: Use this structural and energetic data to establish a critical design principle for engineering next-generation AMPs optimized to combat LPS-induced sepsis and Gram-negative bacterial infections Expected Outcomes 1. Quantitative Validation of Ser09 role in binding: Conclusive quantitative data will establish that the Ser to Ala or Thr mutations at position 9 significantly reduces or eliminates the binding affinity, confirming Ser09 as the molecular anchor. 2. Beta-hairpin structure forming around SER09 in GL13K wild type: Due to role of Ser09 in GL13K-LPS binding, we expect to observe a beta-hairpin structure near c-terminus of GL13K wild type, exposing the Ser09 to LPS binding region. 3. Informed Rational Peptide Design: The combined structural model and quantitative data will establish a critical design principle for optimizing AMPs. This insight will specifically define the functional requirement for an uncharged hydroxyl group at position 9 for high-affinity LPS binding, directly guiding the development of potent, targeted anti-sepsis therapeutics.