Microsecond acquisition of heterogeneous structure in the folding of a TIM barrel protein
- NWU
The earliest kinetic folding events for ({beta}{alpha}){sub 8} barrels reflect the appearance of off-pathway intermediates. Continuous-flow microchannel mixing methods interfaced to small-angle x-ray scattering (SAXS), circular dichroism (CD), time-resolved Foerster resonant energy transfer (trFRET), and time-resolved fluorescence anisotropy (trFLAN) have been used to directly monitor global and specific dimensional properties of the partially folded state in the microsecond time range for a representative ({beta}{alpha}){sub 8} barrel protein. Within 150 {micro}s, the {alpha}-subunit of Trp synthase ({alpha}TS) experiences a global collapse and the partial formation of secondary structure. The time resolution of the folding reaction was enhanced with trFRET and trFLAN to show that, within 30 {micro}s, a distinct and autonomous partially collapsed structure has already formed in the N-terminal and central regions but not in the C-terminal region. A distance distribution analysis of the trFRET data confirmed the presence of a heterogeneous ensemble that persists for several hundreds of microseconds. Ready access to locally folded, stable substructures may be a hallmark of repeat-module proteins and the source of early kinetic traps in these very common motifs. Their folding free-energy landscapes should be elaborated to capture this source of frustration.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1006824
- Journal Information:
- Proc. Natl. Acad. Sci. USA, Vol. 105, Issue (36) ; 2008; ISSN 0027-8424
- Country of Publication:
- United States
- Language:
- ENGLISH
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