title: Folding and association of thermophilic dimeric and trimeric DsrEFH proteins: Tm0979 and Mth1491.
abstract: Although the majority of natural proteins exist as protein-protein complexes, the molecular basis for the formation and regulation of such interactions and the evolution of protein interfaces remain poorly understood. We have investigated these phenomena by characterizing the thermal and chemical denaturation of thermophilic DsrEFH proteins that have a common subunit fold but distinct quaternary structures: homodimeric Tm0979 and homotrimeric Mth1491. Tm0979 forms a moderate affinity dimer, and a monomeric intermediate is readily populated at equilibrium and during folding kinetics. In contrast, the Mth1491 trimer has extremely high stability, so that a monomeric form is not measurably populated at equilibrium, although it may be during folding kinetics. A common mechanism for evolution of quaternary structures may be facile formation of a relatively stable monomeric species, with stabilizing intermolecular interactions centering on alternative environments for a beta-strand at the edge of the monomer, augmented by malleable hydrophobic interactions. The exceptional trimer stability arises from a remarkably slow unfolding rate constant, 6.5 x 10(-13) s(-1), which is a common characteristic of highly stable thermophilic and/or oligomeric proteins. The folding characteristics of Tm0979 and Mth1491 have interesting implications for assembly and regulation of homo- and heterooligomeric proteins in vivo.
authors.affiliation: Guelph-Waterloo Centre for Graduate Work in Chemistry and Biochemistry and Department of Chemistry, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada.
authors.forename: Céline
authors.initials: C
authors.lastname: Galvagnion
authors.forename: Martin T J
authors.initials: MT
authors.lastname: Smith
authors.forename: Aron
authors.initials: A
authors.lastname: Broom
authors.forename: Kenrick A
authors.initials: KA
authors.lastname: Vassall
authors.forename: Gabriela
authors.initials: G
authors.lastname: Meglei
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Gaspar
authors.forename: Peter B
authors.initials: PB
authors.lastname: Stathopulos
authors.forename: Bo
authors.initials: B
authors.lastname: Cheyne
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Meiering
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D002151:Calorimetry; D005453:Fluorescence; D019791:Guanidine / Q000494:pharmacology; D007700:Kinetics; D017014:Methanobacterium / Q000737:chemistry*; D008970:Molecular Weight; D011489:Protein Denaturation / Q000187:drug effects; D017510:Protein Folding / Q000187:drug effects; D055503:Protein Multimerization / Q000187:drug effects; D020673:Protein Renaturation / Q000187:drug effects; D020836:Protein Structure, Quaternary; D017433:Protein Structure, Secondary; D013816:Thermodynamics; D020124:Thermotoga maritima / Q000737:chemistry*
chemical_list: D001426:Bacterial Proteins; D019791:Guanidine