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Proteins tune the reactivity of metal sites; less understood is the impact of association with a redox partner. We demonstrate the utility of carbon-deuterium labels for selective analysis of delicate...

Almost all living organisms on Earth utilize the same 20 amino acids to build their millions of different proteins, even though there are hundreds of amino acids naturally occurring on Earth. Although it is likely that both the prebiotic and the current environment of Earth shaped the selection of these 20 proteinogenic amino acids, environmental conditions on extraterrestrial planets and moons are known to be quite different than those on Earth. In particular, the surfaces of planets and moons such as Mars, Europa and Enceladus have a much greater flux of UV and gamma radiation impacting their surface than that of Earth. Thus, if life were to have evolved extraterrestrially, a different lexicon of amino acids may have been selected due to different environmental pressures, such as higher radiation exposure. One fundamental property an amino acid must have in order to be of use to the evolution of life is relative stability. Therefore, we studied the stability of three different proteinogenic amino acids (tyrosine, phenylalanine and tryptophan) as compared with 20 non-proteinogenic amino acids that were structurally similar to the aromatic proteinogenic amino acids, following ultraviolet (UV) light (254, 302, or 365 nm) and gamma-ray irradiation. The degree of degradation of the amino acids was quantified using an ultra-high performance liquid chromatography-mass spectrometer (UPLC-MS). The result showed that many non-proteinogenic amino acids had either equal or increased stability to certain radiation wavelengths as compared with their proteinogenic counterparts, with fluorinated phenylalanine and tryptophan derivatives, in particular, exhibiting enhanced stability as compared with proteinogenic phenylalanine and tryptophan amino acids following gamma and select UV irradiation.

Cytochrome P450s are diverse and powerful catalysts that can activate molecular oxygen to oxidize a wide variety of substrates. Catalysis relies on effective uptake of two electrons and two protons. For cytochrome P450cam, an archetypal member of the superfamily, the second electron must be supplied by the redox partner putidaredoxin (Pdx). Pdx also plays an effector role beyond electron transfer, but after decades the mechanism remains under investigation. We applied infrared spectroscopy to heme-ligated CN– to examine the influence of Pdx binding. The results indicate that Pdx induces the population of a conformation wherein the CN– ligand forms a strong hydrogen bond to a solvent water molecule, experimentally corroborating the formation of a proposed proton delivery network. Further, characterization of T252A P450cam implicates the side chain of Thr252 in regulating the population equilibrium of hydrogen-bonded states within the P450cam/Pdx complex, which could underlie its role in directing activated oxygen toward product formation and preventing reaction uncoupling through peroxide release.

Determining the mechanism by which Cytochrome P450s (P450s) can catalyze oxidation reactions of substrates with differing specificity and regioselectivity is crucial for aiding drug development and understanding drug metabolism. Cytochrome P450cam (P450cam), a model P450, catalyzes the hydroxylation of d-camphor to 5-exo-hydroxycamphor with high specificity and regioselectivity, it can also act upon camphor-like analogs at the expense of regioselectivity. Previous studies have suggested conformational dynamics may play a role in the recognition and hydroxylation of substrates with varying degrees of regioselectivity. To investigate the role of dynamics in regioselectivity, we characterized P450cam when bound to a camphor and norcamphor, substrates acted upon with 100% and 45% regioselectivity respectively. 2D IR spectroscopy was paired site-specific labeling and used to measure protein side-chain dynamics with high spatial and temporal resolution. Cyanophenylalanine was used as a vibrational probe and incorporated in five distinct locations of P450cam, three sites in the active site and two progressively distal from the active site. The results suggest different parts of the protein active site are preferentially involved in substrate binding and contributions from inhomogeneous broadening are more significant for substrates acted upon with high regioselectivity.