title: Folding and stability of a primitive protein.
abstract: We have previously attempted to simulate domain creation in early protein evolution by recombining polypeptide segments from non-homologous proteins, and we have described the structure of one such de novo protein, 1b11, a segment-swapped tetramer with novel architecture. Here, we have analyzed the thermodynamic stability and folding kinetics of the 1b11 tetramer and its monomeric and dimeric intermediates, and of 1b11 mutants with changes at the domain interface. Denatured 1b11 polypeptides fold into transient, folded monomers with marginal stability (DeltaG<1kcalmol(-1)) which convert rapidly ( approximately 6x10(4)M(-1)s(-1)) into dimers (DeltaG=9.8kcal/mol) and then more slowly ( approximately 3M(-1)s(-1)) into tetramers (DeltaG=28kcalmol(-1)). Segment swapping takes place during dimerization, as suggested by mass spectroscopic analysis of covalently linked peptides derived from proteolysis of a disulfide-linked dimer. Our results confirm that segment swapping and associated oligomerization are both powerful ways of stabilizing proteins, and we suggest that this may have been a feature of early protein evolution.
authors.affiliation: Division of Protein and Nucleic Acid Chemistry, MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK. lutz@mrc-lmb.cam.ac.uk
authors.forename: Lutz
authors.initials: L
authors.lastname: Riechmann
authors.forename: Isabelle
authors.initials: I
authors.lastname: Lavenir
authors.forename: Stephanie
authors.initials: S
authors.lastname: de Bono
authors.forename: Greg
authors.initials: G
authors.lastname: Winter
mesh_terms: D000595:Amino Acid Sequence; D019281:Dimerization; D019020:Directed Molecular Evolution; D019143:Evolution, Molecular; D007700:Kinetics; D008969:Molecular Sequence Data; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000235:genetics; D013816:Thermodynamics
chemical_list: D011506:Proteins