title: Enhanced amphiphilic profile of a short β-stranded peptide improves its antimicrobial activity.
abstract: SB056 is a novel semi-synthetic antimicrobial peptide with a dimeric dendrimer scaffold. Active against both Gram-negative and -positive bacteria, its mechanism has been attributed to a disruption of bacterial membranes. The branched peptide was shown to assume a β-stranded conformation in a lipidic environment. Here, we report on a rational modification of the original, empirically derived linear peptide sequence [WKKIRVRLSA-NH2, SB056-lin]. We interchanged the first two residues [KWKIRVRLSA-NH2, β-SB056-lin] to enhance the amphipathic profile, in the hope that a more regular β-strand would lead to a better antimicrobial performance. MIC values confirmed that an enhanced amphiphilic profile indeed significantly increases activity against both Gram-positive and -negative strains. The membrane binding affinity of both peptides, measured by tryptophan fluorescence, increased with an increasing ratio of negatively charged/zwitterionic lipids. Remarkably, β-SB056-lin showed considerable binding even to purely zwitterionic membranes, unlike the original sequence, indicating that besides electrostatic attraction also the amphipathicity of the peptide structure plays a fundamental role in binding, by stabilizing the bound state. Synchrotron radiation circular dichroism and solid-state 19F-NMR were used to characterize and compare the conformation and mobility of the membrane bound peptides. Both SB056-lin and β-SB056-lin adopt a β-stranded conformation upon binding POPC vesicles, but the former maintains an intrinsic structural disorder that also affects its aggregation tendency. Upon introducing some anionic POPG into the POPC matrix, the sequence-optimized β-SB056-lin forms well-ordered β-strands once electro-neutrality is approached, and it aggregates into more extended β-sheets as the concentration of anionic lipids in the bilayer is raised. The enhanced antimicrobial activity of the analogue correlates with the formation of these extended β-sheets, which also leads to a dramatic alteration of membrane integrity as shown by 31P-NMR. These findings are generally relevant for the design and optimization of other membrane-active antimicrobial peptides that can fold into amphipathic β-strands.
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.
authors.forename: Giorgia
authors.initials: G
authors.lastname: Manzo
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.
authors.forename: Mariano A
authors.initials: MA
authors.lastname: Scorciapino
authors.affiliation: Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology (KIT), POB 3640, 76021 Karlsruhe, Germany.
authors.forename: Parvesh
authors.initials: P
authors.lastname: Wadhwani
authors.affiliation: Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology (KIT), POB 3640, 76021 Karlsruhe, Germany.
authors.forename: Jochen
authors.initials: J
authors.lastname: Bürck
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.
authors.forename: Nicola Pietro
authors.initials: NP
authors.lastname: Montaldo
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.
authors.forename: Manuela
authors.initials: M
authors.lastname: Pintus
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.
authors.forename: Roberta
authors.initials: R
authors.lastname: Sanna
authors.affiliation: Department of Chemical and Geological Sciences, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.
authors.forename: Mariano
authors.initials: M
authors.lastname: Casu
authors.affiliation: Research & Development Unit, Spider Biotech S.r.l., I-10010 Colleretto Giacosa (TO), Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Giuliani
authors.affiliation: Research & Development Unit, Spider Biotech S.r.l., I-10010 Colleretto Giacosa (TO), Italy.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Pirri
authors.affiliation: Dipartimento di Scienze Biochimiche, "A. Rossi Fanelli", Istituto Pasteur-Fondazione Cenci Bolognetti, Sapienza Università di Roma, Rome, Italy.
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Luca
authors.affiliation: Institute of Biological Interfaces (IBG-2), Karlsruhe Institute of Technology (KIT), POB 3640, 76021 Karlsruhe, Germany; Institute of Organic Chemistry, Karlsruhe Institute of Technology (KIT), Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany.
authors.forename: Anne S
authors.initials: AS
authors.lastname: Ulrich
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, Cittadella Universitaria, I-09042 Monserrato (CA), Italy.
authors.forename: Andrea C
authors.initials: AC
authors.lastname: Rinaldi
mesh_terms: D000890:Anti-Infective Agents / Q000737:chemistry / Q000494:pharmacology*; D002942:Circular Dichroism; D004912:Erythrocytes / Q000187:drug effects; D004926:Escherichia coli / Q000187:drug effects; D053878:Hemolytic Agents / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D019906:Nuclear Magnetic Resonance, Biomolecular; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D017433:Protein Structure, Secondary; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D020539:Sequence Analysis, Protein; D013211:Staphylococcus aureus / Q000187:drug effects; D013501:Surface-Active Agents / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000890:Anti-Infective Agents; D053878:Hemolytic Agents; D010455:Peptides; D013501:Surface-Active Agents