title: Computational study of elements of stability of a four-helix bundle protein biosurfactant.
abstract: Biosurfactants are surface-active molecules produced principally by microorganisms. They are a sustainable alternative to chemically-synthesized surfactants, having the advantages of being non-toxic, highly functional, eco-friendly and biodegradable. However they are currently only used in a few industrial products due to costs associated with production and purification, which exceed those for commodity chemical surfactants. DAMP4, a member of a four-helix bundle biosurfactant protein family, can be produced in soluble form and at high yield in Escherichia coli, and can be recovered using a facile thermal phase-separation approach. As such, it encompasses an interesting synergy of biomolecular and chemical engineering with prospects for low-cost production even for industrial sectors. DAMP4 is highly functional, and due to its extraordinary thermal stability it can be purified in a simple two-step process, in which the combination of high temperature and salt leads to denaturation of all contaminants, whereas DAMP4 stays stable in solution and can be recovered by filtration. This study aimed to characterize and understand the fundamental drivers of DAMP4 stability to guide further process and surfactant design studies. The complementary use of experiments and molecular dynamics simulation revealed a broad pH and temperature tolerance for DAMP4, with a melting point of 122.4 °C, suggesting the hydrophobic core as the major contributor to thermal stability. Simulation of systematically created in silico variants of DAMP4 showed an influence of number and location of hydrophilic mutations in the hydrophobic core on stability, demonstrating a tolerance of up to three mutations before a strong loss in stability occurred. The results suggest a consideration of a balance of stability, functionality and kinetics for new designs according to their application, aiming for maximal functionality but at adequate stability to allow for cost-efficient production using thermal phase separation approaches.
authors.affiliation: Centre for Biomolecular Engineering, Australian Institute for Bioengineering and Nanotechnology, The University of Queensland, St Lucia, QLD, 4072, Australia.
authors.forename: Andrea
authors.initials: A
authors.lastname: Schaller
authors.forename: Natalie K
authors.initials: NK
authors.lastname: Connors
authors.forename: Mirjana Dimitrijev
authors.initials: MD
authors.lastname: Dwyer
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Oelmeier
authors.forename: Jürgen
authors.initials: J
authors.lastname: Hubbuch
authors.forename: Anton P J
authors.initials: AP
authors.lastname: Middelberg
mesh_terms: D000595:Amino Acid Sequence; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D057927:Hydrophobic and Hydrophilic Interactions; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D011487:Protein Conformation; D011489:Protein Denaturation; D015202:Protein Engineering / Q000379:methods; D055550:Protein Stability; D011994:Recombinant Proteins / Q000737:chemistry* / Q000378:metabolism; D040681:Structural Homology, Protein; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D011994:Recombinant Proteins; D013501:Surface-Active Agents