title: Adsorption of the natural protein surfactant Rsn-2 onto liquid interfaces.
abstract: To stabilize foams, droplets and films at liquid interfaces a range of protein biosurfactants have evolved in nature. Compared to synthetic surfactants, these combine surface activity with biocompatibility and low solution aggregation. One recently studied example is Rsn-2, a component of the foam nest of the frog Engystomops pustulosus, which has been predicted to undergo a clamshell-like opening transition at the air-water interface. Using atomistic molecular dynamics simulations and surface tension measurements we study the adsorption of Rsn-2 onto air-water and cyclohexane-water interfaces. The protein adsorbs readily at both interfaces, with adsorption mediated by the hydrophobic N-terminus. At the cyclohexane-water interface the clamshell opens, due to the favourable interaction between hydrophobic residues and cyclohexane molecules and the penetration of cyclohexane molecules into the protein core. Simulations of deletion mutants showed that removal of the N-terminus inhibits interfacial adsorption, which is consistent with the surface tension measurements. Deletion of the hydrophilic C-terminus also affects adsorption, suggesting that this plays a role in orienting the protein at the interface. The characterisation of the interfacial behaviour gives insight into the factors that control the interfacial adsorption of proteins, which may inform new applications of this and similar proteins in areas including drug delivery and food technology and may also be used in the design of synthetic molecules showing similar changes in conformation at interfaces.
authors.affiliation: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, UK. c.e.macphee@ed.ac.uk.
authors.forename: Giovanni B
authors.initials: GB
authors.lastname: Brandani
authors.affiliation: School of Chemistry, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Vance
authors.affiliation: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, UK. c.e.macphee@ed.ac.uk.
authors.forename: Marieke
authors.initials: M
authors.lastname: Schor
authors.affiliation: School of Chemistry, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Cooper
authors.affiliation: School of Life Sciences, University of Glasgow, Glasgow, G12 8QQ, UK.
authors.forename: Malcolm W
authors.initials: MW
authors.lastname: Kennedy
authors.affiliation: Institute of Molecular, Cell, and Systems Biology, University of Glasgow, G12 8QQ, UK. brian.smith@glasgow.ac.uk.
authors.forename: Brian O
authors.initials: BO
authors.lastname: Smith
authors.affiliation: School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3FD, UK. c.e.macphee@ed.ac.uk.
authors.forename: Cait E
authors.initials: CE
authors.lastname: MacPhee
authors.affiliation: Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, G1 1XL, UK and School of Chemistry, National University of Ireland Galway, Galway, Ireland. david.cheung@nuigalway.ie.
authors.forename: David L
authors.identifier: http://orcid.org/0000-0002-3994-2295
authors.initials: DL
authors.lastname: Cheung
mesh_terms: D000327:Adsorption; D000388:Air; D029845:Amphibian Proteins / Q000737:chemistry*; D003510:Cyclohexanes / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D029845:Amphibian Proteins; D003510:Cyclohexanes; C000617978:ranaspumin-2 protein, Engystomops pustulosus; D014867:Water; C506365:Cyclohexane