Cytochrome c-b562 belongs to an interesting family of four-helix bundle cytochromes that have nearly identical structures yet widely divergent folding pathways, creating a unique opportunity to study the relationship between primary sequences and folding in proteins with similar topologies.  We characterize the dynamics of cytochrome c-b562 through a combination of electron transfer and fluorescence energy transfer (FET). The dynamics of intrachain diffusion in unfolded cytochromes are probed by monitoring contact quenching of a photoexcited, covalently-bound [Ru(bpy)2(IA-phen)]2+ dye by the heme FeIII.  Rates of electron transfer and recombination following nanosecond laser pulses are measured via the luminescence decay of *RuII and transient absorption of the heme.We resolve fast folding by coupling time-resolved FET with an ultrafast continuous flow mixer.  FET occurs between a small, covalently-bound dansyl fluorophore and the heme.  Fitting the dansyl fluorescence decay following picosecond laser excitation provides us with time-dependent dansyl-heme distance distributions during the folding process.

Conformational populations and dynamics of a fast folding cytochrome captured by electron transfer and time-resolved fluorescence energy transfer

241st National Meeting (2011)

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