title: Evidence for an obligatory intermediate in the folding of interleukin-1 beta.
abstract: The folding of the beta-sheet protein, interleukin-1 beta, was examined at pH 5.0 and 25 degrees C using pulse-labelling hydrogen exchange and electrospray ionization mass spectrometric analysis, as well as stopped-flow circular dichroism and fluorescence spectroscopies. The first detectable event is the formation of a partially folded intermediate in a kinetic step with a relaxation time of 126 +/- 26 ms. There is a lag in native protein production of at least 400 ms. Optical studies indicate that the intermediate is converted to the native species in a reaction with a relaxation time of 43 +/- 5 s. The kinetic rates determined from stopped-flow fluorescence, circular dichroism and pulse-labelling experiments are similar and consistent with a simple sequential model for the folding pathway of interleukin-1 beta at pH 5.0 and 25 degrees C. Taken together, our data provide kinetic evidence that formation of the native state of interleukin-1 beta proceeds through an obligatory intermediate. We explain our results in terms of the classical and new views of protein folding.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla 92093-0359, USA.
authors.forename: D K
authors.initials: DK
authors.lastname: Heidary
authors.forename: L A
authors.initials: LA
authors.lastname: Gross
authors.forename: M
authors.initials: M
authors.lastname: Roy
authors.forename: P A
authors.initials: PA
authors.lastname: Jennings
mesh_terms: D007375:Interleukin-1 / Q000737:chemistry*; D007700:Kinetics; D013058:Mass Spectrometry / Q000379:methods; D017510:Protein Folding
chemical_list: D007375:Interleukin-1