AVS 46th International Symposium
    Biomaterial Interfaces Group Tuesday Sessions
       Session BI-TuM

Paper BI-TuM9
Surface Orientation of Peptides with @alpha@-helix and @beta@-sheet Secondary Structures on Fluorocarbon Substrates

Tuesday, October 26, 1999, 11:00 am, Room 613/614

Session: Protein Solid-Surface Interactions II
Presenter: L. Gamble, University of Washington
Authors: L. Gamble, University of Washington
J.R. Long, University of Washington
P.S. Stayton, University of Washington
D.A. Fischer, National Institute of Standards and Technology
D.G. Castner, University of Washington
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The orientation of surface bound proteins can have a significant effect of their function. To aid with the interpretation of Near edge X-ray absorption fine structure (NEXAFS) spectra from adsorbed protein films we haved studied short, well-defined peptide "standards." NEXAFS is a surface sensitive technique that has been used to determine the orientation of polymers and self-assembled monolayers. Here NEXAFS is used to determine the surface orientation of short peptides chains designed to adsorb in @alpha@-helical and @beta@-sheet conformations on hydrophobic surfaces. The N K-edge spectra show an orientation dependence of the N1s to @pi@* peak between the 90° and 20° incident x-ray angles for both peptides adsorbed onto highly-ordered poly(tetrafluoroethylene) (PTFE) surfaces. The results indicate that the @beta@-sheet peptide is adsorbed with the peptide backbone "parallel" to the substrate, while the @alpha@-helix adsorbes with the helical axis parallel to the substrate. Spectra of the O K-edge support these results. The lack of orientational dependence seen for these same peptides adsorbed onto a disordered fluoropolymer surface containing different types of fluorocarbon species indicates the degree of substrate order and/or the type of surface functional groups play a key role in determining the degree of ordering in the adsorbed peptides. NEXAFS spectra were also used to distinguish between the secondary structures of the two peptides. Preliminary NEXAFS results from adsorbed protein films show that orientataion of the peptide backbone is only observed for non-gobular proteins such as fibrogen and fibronectin. Gobular proteins such as albumin do not exhibit any preferrential orientation, even on highly-ordered substrates.