Biomaterial Database

Probing the orientation and conformation of alpha-helix and beta-strand model peptides on self-assembled monolayers using sum frequency generation and NEXAFS spectroscopy. 2010

Tobias Weidner, and Julia S Apte, and Lara J Gamble, and David G Castner

National ESCA and Surface Analysis Center for Biomedical Problems, Department of Bioengineering, Box 351750, University of Washington, Seattle, Washington 98195, USA.

The structure and orientation of amphiphilic alpha-helix and beta-strand model peptide films on self-assembled monolayers (SAMs) have been studied with sum frequency generation (SFG) vibrational spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The alpha-helix peptide is a 14-mer, and the beta-strand is a 15-mer of hydrophilic lysine and hydrophobic leucine residues with hydrophobic periodicities of 3.5 and 2, respectively. These periodicities result in the leucine side chains located on one side of the peptides and the lysine side chains on the other side. The SAMs were prepared from the assembly of either carboxylic acid- or methyl-terminated alkyl thiols onto gold surfaces. For SFG studies, the deuterated analog of the methyl SAM was used. SFG vibrational spectra in the C-H region of air-dried peptides films on both SAMs exhibit strong peaks near 2965, 2940, and 2875 cm(-1) related to ordered leucine side chains. The orientation of the leucine side chains was determined from the phase of these features relative to the nonresonant gold background. The relative phase for both the alpha-helix and beta-strand peptides showed that the leucine side chains were oriented away from the carboxylic acid SAM surface and oriented toward the methyl SAM surface. Amide I peaks observed near 1656 cm(-1) for the alpha-helix peptide confirm that the secondary structure is preserved on both SAMs. Strong linear dichroism related to the amide pi* orbital at 400.8 eV was observed in the nitrogen K-edge NEXAFS spectra for the adsorbed beta-strand peptides, suggesting that the peptide backbones are oriented parallel to the SAM surface with the side chains pointing toward or away from the interface. For the alpha-helix the dichroism of the amide pi* is significantly weaker, probably because of the broad distribution of amide bond orientations in the alpha-helix secondary structure.

UI	MeSH Term	Description	Entries
D008969	Molecular Sequence Data	Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.	Sequence Data, Molecular,Molecular Sequencing Data,Data, Molecular Sequence,Data, Molecular Sequencing,Sequencing Data, Molecular
D010455	Peptides	Members of the class of compounds composed of AMINO ACIDS joined together by peptide bonds between adjacent amino acids into linear, branched or cyclical structures. OLIGOPEPTIDES are composed of approximately 2-12 amino acids. Polypeptides are composed of approximately 13 or more amino acids. PROTEINS are considered to be larger versions of peptides that can form into complex structures such as ENZYMES and RECEPTORS.	Peptide,Polypeptide,Polypeptides
D000327	Adsorption	The adhesion of gases, liquids, or dissolved solids onto a surface. It includes adsorptive phenomena of bacteria and viruses onto surfaces as well. ABSORPTION into the substance may follow but not necessarily.	Adsorptions
D000595	Amino Acid Sequence	The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.	Protein Structure, Primary,Amino Acid Sequences,Sequence, Amino Acid,Sequences, Amino Acid,Primary Protein Structure,Primary Protein Structures,Protein Structures, Primary,Structure, Primary Protein,Structures, Primary Protein
D014732	Vibration	A continuing periodic change in displacement with respect to a fixed reference. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)	Vibrations
D017433	Protein Structure, Secondary	The level of protein structure in which regular hydrogen-bond interactions within contiguous stretches of polypeptide chain give rise to ALPHA-HELICES; BETA-STRANDS (which align to form BETA-SHEETS), or other types of coils. This is the first folding level of protein conformation.	Secondary Protein Structure,Protein Structures, Secondary,Secondary Protein Structures,Structure, Secondary Protein,Structures, Secondary Protein
D056928	X-Ray Absorption Spectroscopy	Analysis of the energy absorbed across a spectrum of x-ray energies/wavelengths to determine the chemical structure and electronic states of the absorbing medium.	Near Edge X-Ray Absorption Fine Structure Spectroscopy,NEXAFS Spectroscopy,Near-Edge X-Ray Absorption Fine Structure Spectroscopy,X-Ray Absorption Near Edge Structure Spectroscopy,X-Ray Absorption Near-Edge Structure Spectroscopy,XANES Spectroscopy,Absorption Spectroscopy, X-Ray,Near Edge X Ray Absorption Fine Structure Spectroscopy,Spectroscopy, NEXAFS,Spectroscopy, X-Ray Absorption,Spectroscopy, XANES,X Ray Absorption Near Edge Structure Spectroscopy,X Ray Absorption Spectroscopy