title: Trp-Cage Folding on Organic Surfaces.
abstract: Trp-cage is an artificial miniprotein that is small, stable, and fast folding due to concerted hydrophobic shielding of a Trp residue by polyproline helices. Simulations have extensively characterized Trp-cage; however, the interactions of Trp-cage with organic surfaces (e.g., membranes) and their effect on protein conformation are largely unknown. To better understand these interactions we utilized a combination of replica-exchange molecular dynamics (REMD) and metadynamics (MetaD), to investigate Trp-cage folding on self-assembled monolayers (SAMs). We found that, with REMD and MetaD, Trp-cage strongly binds to neutral CH3 surfaces (-25kT) and moderately adsorbs to anionic COOH interfaces (-7.6kT), with hydrophobic interactions driving CH3 adhesion and electrostatic attractions driving COOH adhesion. Similar to solid-state surfaces, SAMs facilitate a number of intermediate Trp-cage conformations between folded and unfolded states. Regarding Trp-cage's aromatic groups in neutral CH3 systems, Tyr becomes oriented parallel to the surface in order to maximize hydrophobic interactions while Trp remains caged perpendicular to the surface; however, Trp can reorient itself parallel to the interface as the miniprotein more closely binds to the surface. In contrast, Tyr and Trp are both repelled from COOH surfaces, though the Trp-cage still adheres to the anionic interface via Lys and its N-terminated Asn residue.
authors.affiliation: †Department of Physics, University of California Santa Barbara, Santa Barbara, California 93106, United States.|‡Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106, United States.
authors.forename: Zachary A
authors.initials: ZA
authors.lastname: Levine
authors.affiliation: §Department of Chemical Engineering, University of Washington, Seattle, Washington 98105, United States.
authors.forename: Sean A
authors.initials: SA
authors.lastname: Fischer
authors.affiliation: †Department of Physics, University of California Santa Barbara, Santa Barbara, California 93106, United States.|‡Department of Chemistry and Biochemistry, University of California Santa Barbara, Santa Barbara, California 93106, United States.
authors.forename: Joan-Emma
authors.initials: JE
authors.lastname: Shea
authors.affiliation: §Department of Chemical Engineering, University of Washington, Seattle, Washington 98105, United States.
authors.forename: Jim
authors.initials: J
authors.lastname: Pfaendtner
mesh_terms: D000595:Amino Acid Sequence; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D009930:Organic Chemicals / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D017510:Protein Folding; D055550:Protein Stability; D017433:Protein Structure, Secondary; D013499:Surface Properties
chemical_list: D009930:Organic Chemicals; D010455:Peptides; C508725:Trp-cage peptide