Article pubs.acs.org/Langmuir
The Influence of Amino Acid Sequence and Functionality on the Binding Process of Peptides onto Gold Surfaces Jing Yu, Matthew L. Becker,* and Gustavo A. Carri* Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909, United States
ABSTRACT: We present a molecular dynamics study of the binding process of peptide A3 (AYSSGAPPMPPF) and other similar peptides onto gold surfaces, and identify the functions of many amino acids. Our results provide a clear picture of the separate regimes present in the binding process: diffusion, anchoring, crawling and binding. Moreover, we explored the roles of individual residues. We found that tyrosine, methionine, and phenylalanine are strong binding residues; serine serves as an effective anchoring residue; proline acts as a dynamic anchoring point, while glycine and alanine give flexibility to the peptide backbone. We then show that our findings apply to unrelated phage-derived sequences that have been reported recently to facilitate AuNP synthesis. This new knowledge may aid in the design of new peptides for the synthesis of gold nanostructures with novel morphologies.
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INTRODUCTION Noble metal nanoparticles, especially gold, are finding use in molecular-specific probes, bioimaging, cancer diagnostics and therapeutics across the biomedical spectrum due to their surface-plasmon resonance-enhanced optical and thermal properties.1 Gold nanoparticles (AuNPs) exhibit narrow and intense absorption and scattering bands due to their plasmonic properties, which arise when an electromagnetic field drives the collective oscillations of a AuNP’s free electrons into resonance.2 The plasmonic properties are highly dependent on shape and structure (solid or core−shell) of the nanomaterial. Spherical AuNPs have a single plasmon resonant extinction peak at around 520 nm. Rod-shaped NPs exhibit two plasmon resonances due to oscillation of the conduction electrons along the short (transverse) axis as well as along the long (longitudinal) axis of the particles. The longitudinal band is red-shifted with the extent dependent on the aspect ratio of the nanorod.3 The intense scattering and absorption of light coupled with the ability to tailor the extinction peaks from the visible to infrared wavelength regions using aspect ratio makes anisotropic structures extremely attractive as contrast agents for optical imaging techniques.4 These applications are being enabled through new synthetic approaches, which have facilitated well-defined morphologies and surface functionality useful in both targeting and therapeutics in high yields. As an alternative to reducing conditions that are toxic to biological systems, many bioassisted © 2011 American Chemical Society
synthesis routes have been demonstrated which render welldefined AuNPs.5 These methods often employ reducing agents, including amino acids, simple primary amines,6 and polymers7 which are less harsh. Future innovations in the field of imaging and image contrast will require similar advances in our understanding of processes governing AuNP synthesis and the chemical and biomimetic methods to assemble complex geometries such as rods, shells, and stars.8 Metal selective peptides identified via phage display have become increasingly useful in this regard, generating a number of noble metal nanostructures.9 Molecular dynamics (MD) simulation studies have shown the varying effects of metal (Au, Pt, Pd, etc.), surface facets ({111}, {100}), as well as peptide properties (length, flexibility and stability) on the gold−peptide interactions.10 Naik et al. identified a 12-residue peptide AYSSGAPPMPPF (A3) that yielded small (
