title: NMR structure of temporin-1 ta in lipopolysaccharide micelles: mechanistic insight into inactivation by outer membrane.
abstract: BACKGROUND
  Antimicrobial peptides (AMPs) play important roles in the innate defense mechanism. The broad spectrum of activity of AMPs requires an efficient permeabilization of the bacterial outer and inner membranes. The outer leaflet of the outer membrane of Gram negative bacteria is made of a specialized lipid called lipopolysaccharide (LPS). The LPS layer is an efficient permeability barrier against anti-bacterial agents including AMPs. As a mode of protection, LPS can induce self associations of AMPs rendering them inactive. Temporins are a group of short-sized AMPs isolated from frog skin, and many of them are inactive against Gram negative bacteria as a result of their self-association in the LPS-outer membrane.
  
  
  RESULTS
  Using NMR spectroscopy, we have determined atomic resolution structure and characterized localization of temporin-1Ta or TA (FLPLIGRVLSGIL-amide) in LPS micelles. In LPS micelles, TA adopts helical conformation for residues L4-I12, while residues F1-L3 are found to be in extended conformations. The aromatic sidechain of residue F1 is involved in extensive packing interactions with the sidechains of residues P3, L4 and I5. Interestingly, a number of long-range NOE contacts have been detected between the N-terminal residues F1, P3 with the C-terminal residues S10, I12, L13 of TA in LPS micelles. Saturation transfer difference (STD) NMR studies demonstrate close proximity of residues including F1, L2, P3, R7, S10 and L13 with the LPS micelles. Notably, the LPS bound structure of TA shows differences with the structures of TA determined in DPC and SDS detergent micelles.
  
  
  CONCLUSIONS
  We propose that TA, in LPS lipids, forms helical oligomeric structures employing N- and C-termini residues. Such oligomeric structures may not be translocated across the outer membrane; resulting in the inactivation of the AMP. Importantly, the results of our studies will be useful for the development of antimicrobial agents with a broader spectrum of activity.
authors.affiliation: School of Biological Sciences, Nanyang Technological University, Singapore, Singapore.
authors.forename: Rathi
authors.initials: R
authors.lastname: Saravanan
authors.forename: Mangesh
authors.initials: M
authors.lastname: Joshi
authors.forename: Harini
authors.initials: H
authors.lastname: Mohanram
authors.forename: Anirban
authors.initials: A
authors.lastname: Bhunia
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: Mangoni
authors.forename: Surajit
authors.initials: S
authors.lastname: Bhattacharjya
mesh_terms: D000890:Anti-Infective Agents / Q000737:chemistry / Q000378:metabolism; D023181:Antimicrobial Cationic Peptides / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D008070:Lipopolysaccharides / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008823:Micelles; D008958:Models, Molecular; D015394:Molecular Structure; D055503:Protein Multimerization; D011506:Proteins / Q000737:chemistry* / Q000378:metabolism; D012996:Solutions; D055672:Static Electricity
chemical_list: D000890:Anti-Infective Agents; D023181:Antimicrobial Cationic Peptides; D008070:Lipopolysaccharides; D008823:Micelles; D011506:Proteins; D012996:Solutions; C104501:temporin
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