title: Sodium sulphate reactivates a protein A minidomain with a short elastin beta-turn.
abstract: Elastin polymer sequences derived from muscle exhibit temperature and salt-induced reversible contractions and expansions. A folded and contracted beta-turn helical elastin structure is stabilised by increased intramolecular hydrophobic interactions. We have generated a switchable binding protein by inserting a typical elastin turn sequence, GVPGVG, between the two IgG-binding helices of an engineered globular minidomain from Protein A. This mutant showed increased binding of IgG-molecules compared to the wild-type sequence in the presence of sodium sulphate, as measured by surface plasmon resonance spectroscopy. Analysis by circular dichroism revealed a salt-induced folding of the mutant minidomain to a native type I beta-turn, likely stabilised as a result of the two interacting dehydrated valines across the beta-turn. Since sodium sulphate can be successfully used to regulate the folding/unfolding or binding/dissociation of this minidomain, this suggests an alternative protein purification method.
authors.affiliation: Department of Biology and Biochemistry, University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom.
authors.forename: H
authors.initials: H
authors.lastname: Reiersen
authors.forename: A R
authors.initials: AR
authors.lastname: Rees
mesh_terms: D000595:Amino Acid Sequence; D002942:Circular Dichroism; D004549:Elastin / Q000737:chemistry* / Q000235:genetics; D007074:Immunoglobulin G / Q000276:immunology; D007700:Kinetics; D016296:Mutagenesis / Q000235:genetics; D009994:Osmolar Concentration; D011489:Protein Denaturation; D015202:Protein Engineering; D017510:Protein Folding; D017433:Protein Structure, Secondary / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D012997:Solvents; D013205:Staphylococcal Protein A / Q000737:chemistry* / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013431:Sulfates / Q000494:pharmacology*; D020349:Surface Plasmon Resonance; D013696:Temperature; D013816:Thermodynamics; D014867:Water / Q000378:metabolism
chemical_list: D007074:Immunoglobulin G; D012997:Solvents; D013205:Staphylococcal Protein A; D013431:Sulfates; D014867:Water; C012036:sodium sulfate; D004549:Elastin