title: Multiple orientation of melittin inside a single lipid bilayer determined by combined vibrational spectroscopic studies.
abstract: Despite the availability of several mature structure determination techniques for bulk proteins, determination of structural and orientational information of interfacial proteins, e.g., in cell membranes or on biomaterial surfaces, remains a difficult problem. We combine sum frequency generation (SFG) vibrational spectroscopy with attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) to investigate the orientation of alpha-helical peptides reconstituted in substrate supported lipid bilayers. Melittin was chosen as a model for alpha-helical peptides, and its orientation when interacting with a supported 1,2-dipalmitoyl-sn-glycero-3-phosphoglycerol (DPPG) bilayer has been examined. Through polarization analysis using amide I signals obtained from both SFG and ATR-FTIR measurements, the orientation distribution of melittin inside a DPPG bilayer was deduced using several trial distribution functions. Melittin was modeled as either an ideal helix or a helix with a bent structure. It was found that a simple distribution function such as a delta-distribution or a Gaussian distribution was not adequate to describe the melittin orientation distribution inside a DPPG bilayer. Instead, two populations of melittin, corresponding to two melittin-bilayer association states, could be used to interpret the experimentally observed result. The method employed in this study demonstrates the feasibility of acquiring a more accurate orientation distribution of peptides/proteins in situ using a combination of vibrational spectroscopic techniques without exogenous labeling.
authors.affiliation: Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Chen
authors.forename: Jie
authors.initials: J
authors.lastname: Wang
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Boughton
authors.forename: Cornelius B
authors.initials: CB
authors.lastname: Kristalyn
authors.forename: Zhan
authors.initials: Z
authors.lastname: Chen
mesh_terms: D008051:Lipid Bilayers / Q000737:chemistry*; D008555:Melitten / Q000737:chemistry*; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D010715:Phosphatidylglycerols / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods*; D013499:Surface Properties
chemical_list: D008051:Lipid Bilayers; D010455:Peptides; D010715:Phosphatidylglycerols; D008555:Melitten; C030345:1,2-dipalmitoylphosphatidylglycerol