Key result
Reaction of [2Fe2S]-containing spinach ferredoxin I with nitric oxide at pH 6.0 favored the formation of protein-bound Roussin's Red Ester over dinitrosyl iron complex in the presence of trace O2.
Infrared spectroscopy demonstrates that trace O2 plays a critical role in determining the products of iron-sulfur protein nitrosylation, potentially relevant to how pathogens sense NO during mammalian immune responses.
May inform pathogen NO-sensing models in immunity; leaves open extension to mammalian iron-sulfur proteins.
We use infrared spectroscopy to demonstrate the critical role that trace O2 plays in determining the products formed when a [2Fe2S] cluster protein reacts with nitric oxide (NO). The observed importance of O2 may have physiological relevance, as many pathogens sense NO using iron-sulfur proteins and will be exposed to NO in an aerobic environment during a mammalian immune response. We show that the [2Fe2S]-containing spinach ferredoxin I undergoes reaction with NO at pH 6.0, with the proportion of protein-bound Roussin's Red Ester compared to the dinitrosyl iron complex product favored by trace O2. Roussin's Red Ester is also favored on nitrosylation in the presence of the thiolate scavenging reagent, iodoacetamide, suggesting that the role of O2 is in oxidative sequestration of cysteine thiolates. Infrared spectroscopy has been overlooked as a tool for studying iron-sulfur protein nitrosylation despite the fact that there exists a wealth of infrared spectroscopic data on small-molecule nitrosyl clusters which serve as models for the identification of protein-bound nitrosyl clusters.
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Grabarczyk et al. (2014) studied this question. Nitric oxide and trace O2 was evaluated on Proportion of protein-bound Roussin's Red Ester compared to the dinitrosyl iron complex product. Reaction of [2Fe2S]-containing spinach ferredoxin I with nitric oxide at pH 6.0 favored the formation of protein-bound Roussin's Red Ester over dinitrosyl iron complex in the presence of trace O2.
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