Heme cofactors in proteins usually display distortions from planarity, and it has been proposed that distortions play a role in determining reactivity. In cytochromes c, the heme cofactor is ruffled, but the effect of ruffling on function has not been clear. To better understand the effects of ruffling on heme properties, cytochrome c variants with different amounts of ruffling have been prepared and studied using electrochemistry, nuclear magnetic resonance (NMR), nuclear resonance vibrational spectroscopy (NRVS), vibrational coherence spectroscopy (VCS), resonance Raman, and transient absorption spectroscopy. The results indicate that increasing ruffling increases porphyrin ligand field strength and decreases reduction potential. Furthermore, ruffling decreases delocalization of Fe d(π)-based molecular orbitals to the β-pyrrole carbons, resulting in decreased coupling to redox partners and lower electron transfer rates. In addition, ruffling influences iron vibrational dynamics, which are strongly coupled to polypeptide vibrations. These results provide a basis for understanding the effect of cytochrome c association with membranes on heme conformation and electron transfer activity.

Effects of heme ruffling on vibrational dynamics, electronic structure, and electronic coupling

249th National Meeting (2015)

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