Solution and Solid-State Nuclear Magnetic Resonance Structural Investigations of the Antimicrobial Designer Peptide GL13K in Membranes

• Published in: Biochemistry (Easton) 2017-08, Vol.56 (32), p.4269-4278
• Main Authors: Harmouche, Nicole, Aisenbrey, Christopher, Porcelli, Fernando, Xia, Youlin, Nelson, Sarah E. D, Chen, Xi, Raya, Jesus, Vermeer, Louic, Aparicio, Conrado, Veglia, Gianluigi, Gorr, Sven-Ulrik, Bechinger, Burkhard
• Format: Article
• Language: English
• Subjects: Antimicrobial Cationic Peptides - chemistry; Humans; Nuclear Magnetic Resonance, Biomolecular; Protein Structure, Secondary; Salivary Proteins and Peptides - chemistry
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/acs.biochem.7b00526

The antimicrobial peptide GL13K encompasses 13 amino acid residues and has been designed and optimized from the salivary protein BPIFA2 to exhibit potent bacteriocidal and anti-biofilm activity against Gram-negative and Gram-positive bacteria as well as anti-lipopolysaccharide activity in vitro and in vivo. Here, the peptide was analyzed in a variety of membrane environments by circular dichroism spectroscopy and by high-resolution multidimensional solution nuclear magnetic resonance (NMR) spectroscopy. Whereas in the absence of membranes a random coil conformation predominates, the peptide adopts a helical structure from residue 5 to 11 in the presence of dodecylphosphocholine micelles. In contrast, a predominantly β-sheet structure was observed in the presence of lipid bilayers carrying negatively charged phospholipids. Whereas 15N solid-state NMR spectra are indicative of a partial alignment of the peptide 15N–1H vector along the membrane surface, 2H and 31P solid-state NMR spectra indicate that in this configuration the peptide exhibits pronounced disordering activities on the phospholipid membrane, which is possibly related to antimicrobial action. GL13K, thus, undergoes a number of conformational transitions, including a random coil state in solution, a helical structure upon dilution at the surface of zwitterionic membranes, and β-sheet conformations at high peptide:lipid ratios.