title: Structure-function relationships in histidine-rich antimicrobial peptides from Atlantic cod.
abstract: Gad-1 and Gad-2 are antimicrobial peptide (AMP) sequences encoded by paralogous genes. They are rich in histidine, which suggests that their activity might be pH-dependent. We examined their structure-function relationships with a view to learning how to improve AMP therapeutic ratios. Activity assays with Gram-negative bacteria and cancer cell lines demonstrate that Gad-2 is substantially more active at slightly acidic pH than it is at neutral pH. By contrast, the activity of Gad-1 at lower pH is similar to its activity at pH7. Circular dichroism spectra indicate that the greater functional plasticity of Gad-2 correlates with a greater structural plasticity; Gad-2's percent helicity varies dramatically with altered pH and lipid environment. Interestingly, Gad-2's highest levels of helicity do not correspond to the conditions where it is most active. High resolution solution NMR structures were determined in SDS micelles at pH5, conditions that induce an intermediate level of helicity in the peptides. Gad-1 is more helical than Gad-2, with both peptides exhibiting the greatest helical tendencies in their central region and lowest helicity in their N-termini. The high resolution structures suggest that maximum activity relies on the appropriate balance between an N-terminal region with mixed hydrophobic/hydrophilic structure features and an amphipathic central and C-terminal region. Taken together with previous studies, our results suggest that to improve the therapeutic ratio of AMPs, consideration should be given to including sequential histidine-pairs, keeping the overall charge of the peptide modest, and retaining a degree of structural plasticity and imperfect amphipathicity.
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: McDonald
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Mannion
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Damien
authors.initials: D
authors.lastname: Pike
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Krystina
authors.initials: K
authors.lastname: Lewis
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Flynn
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Alex M
authors.initials: AM
authors.lastname: Brannan
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Mitchell J
authors.initials: MJ
authors.lastname: Browne
authors.affiliation: Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Donna
authors.initials: D
authors.lastname: Jackman
authors.affiliation: Department of Microbiology and Immunology, Dalhousie University, Canada.
authors.forename: Laurence
authors.initials: L
authors.lastname: Madera
authors.affiliation: Department of Pathology, Dalhousie University, Canada.
authors.forename: Melanie R
authors.initials: MR
authors.lastname: Power Coombs
authors.affiliation: Department of Pathology, Dalhousie University, Canada; Department of Microbiology and Immunology, Dalhousie University, Canada; Department of Surgery, Dalhousie University, Canada.
authors.forename: David W
authors.initials: DW
authors.lastname: Hoskin
authors.affiliation: Ocean Sciences Centre, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Rise
authors.affiliation: Department of Physics and Physical Oceanography, Memorial University of Newfoundland, St. John's, NL A1B 3X9, Canada. Electronic address: vbooth@mun.ca.
authors.forename: Valerie
authors.initials: V
authors.lastname: Booth
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry* / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D002942:Circular Dichroism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000187:drug effects / Q000254:growth & development; D029941:Fish Proteins / Q000737:chemistry* / Q000494:pharmacology; D048389:Gadus morhua / Q000378:metabolism*; D006461:Hemolysis / Q000187:drug effects; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D009682:Magnetic Resonance Spectroscopy; D051379:Mice; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000494:pharmacology; D017433:Protein Structure, Secondary; D013329:Structure-Activity Relationship
chemical_list: D023181:Antimicrobial Cationic Peptides; D029941:Fish Proteins; D020033:Protein Isoforms
keywords: Antimicrobial peptide; Cancer cell killing; Circular dichroism; Minimal inhibitory concentration (MIC) assay; Peptide structure; Solution NMR