title: The Conformation of Interfacially Adsorbed Ranaspumin-2 Is an Arrested State on the Unfolding Pathway.
abstract: Ranaspumin-2 (Rsn-2) is a surfactant protein found in the foam nests of the túngara frog. Previous experimental work has led to a proposed model of adsorption that involves an unusual clam-shell-like unhinging of the protein at an interface. Interestingly, there is no concomitant denaturation of the secondary structural elements of Rsn-2 with the large-scale transformation of its tertiary structure. In this work we use both experiment and simulation to better understand the driving forces underpinning this unusual process. We develop a modified Gō-model approach where we have included explicit representation of the side chains to realistically model the interaction between the secondary structure elements of the protein and the interface. Doing so allows for the study of the underlying energy landscape that governs the mechanism of Rsn-2 interfacial adsorption. Experimentally, we study targeted mutants of Rsn-2, using the Langmuir trough, pendant drop tensiometry, and circular dichroism, to demonstrate that the clam-shell model is correct. We find that Rsn-2 adsorption is in fact a two-step process: the hydrophobic N-terminal tail recruits the protein to the interface after which Rsn-2 undergoes an unfolding transition that maintains its secondary structure. Intriguingly, our simulations show that the conformation Rsn-2 adopts at an interface is an arrested state along the denaturation pathway. More generally, our computational model should prove a useful, and computationally efficient, tool in studying the dynamics and energetics of protein-interface interactions.
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.
authors: Ryan J
authors: RJ
authors: Morris
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.
authors: Giovanni B
authors: GB
authors: Brandani
authors: School of Life Sciences, University of Glasgow, Glasgow, UK.
authors: Vibhuti
authors: V
authors: Desai
authors: School of Life Sciences, University of Glasgow, Glasgow, UK.
authors: Brian O
authors: BO
authors: Smith
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK.
authors: Marieke
authors: M
authors: Schor
authors: School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK. Electronic address: cait.macphee@ed.ac.uk.
authors: Cait E
authors: CE
authors: MacPhee
mesh_terms: D000327:Adsorption; D029845:Amphibian Proteins / Q000737:chemistry*; D008958:Models, Molecular; D011487:Protein Conformation; D058767:Protein Unfolding; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D029845:Amphibian Proteins; C000617978:ranaspumin-2 protein, Engystomops pustulosus