Forsyth, William R.Bilsel, OsmanGu, ZhenyuMatthews, C. Robert2022-08-232022-08-232007-07-102010-03-17J Mol Biol. 2007 Sep 7;372(1):236-53. Epub 2007 Jun 14. <a href="http://dx.doi.org/10.1016/j.jmb.2007.06.018">Link to article on publisher's site</a>0022-2836 (Linking)10.1016/j.jmb.2007.06.01817619021https://hdl.handle.net/20.500.14038/25984The relative contributions of chain topology and amino acid sequence in directing the folding of a (betaalpha)(8) TIM barrel protein of unknown function encoded by the Bacillus subtilis iolI gene (IOLI) were assessed by reversible urea denaturation and a combination of circular dichroism, fluorescence and time-resolved fluorescence anisotropy spectroscopy. The equilibrium reaction for IOLI involves, in addition to the native and unfolded species, a stable intermediate with significant secondary structure and stability and self-associated forms of both the native and intermediate states. Global kinetic analysis revealed that the unfolded state partitions between an off-pathway refolding intermediate and the on-pathway equilibrium intermediate early in folding. Comparisons with the folding mechanisms of two other TIM barrel proteins, indole-3-glycerol phosphate synthase from the thermophile Sulfolobus solfataricus (sIGPS) and the alpha subunit of Escherichia coli tryptophan synthase (alphaTS), reveal striking similarities that argue for a dominant role of the topology in both early and late events in folding. Sequence-specific effects are apparent in the magnitudes of the relaxation times and relative stabilities, in the presence of additional monomeric folding intermediates for alphaTS and sIGPS and in rate-limiting proline isomerization reactions for alphaTS.en-USAmino Acid SequenceAnisotropy*Bacillus subtilisBacterial ProteinsKineticsModels, MolecularMolecular Sequence Data*Protein FoldingProtein Structure, TertiarySequence Homology, Amino AcidTemperatureBiochemistry, Biophysics, and Structural BiologyPharmacology, Toxicology and Environmental HealthJournal Articlehttps://escholarship.umassmed.edu/bmp_pp/1141228626bmp_pp/114