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RNases are among the most stable proteins in nature. They even refold spontaneously after heat inactivation, regaining full activity. Due to their stability and universal presence, they often pose a problem when experimenting with RNA. We investigated the capabilities of nonthermal atmospheric-pressure plasmas to inactivate RNase A and studied the inactivation mechanism on a molecular level. While prolonged heating above 90 °C is required for heat inactivating RNase A, direct plasma treatment with a dielectric barrier discharge (DBD) source caused permanent inactivation within minutes. Circular dichroism spectroscopy showed that DBD-treated RNase A unfolds rapidly. Raman spectroscopy indicated methionine modifications and formation of sulfonic acid. A mass spectrometry-based analysis of the protein modifications that occur during plasma treatment over time revealed that methionine sulfoxide formation coincides with protein inactivation. Chemical reduction of methionine sulfoxides partially restored RNase A activity confirming that sulfoxidation is causal and sufficient for RNase A inactivation. Continued plasma exposure led to over-oxidation of structural disulfide bonds. Using antibodies, disulfide bond over-oxidation was shown to be a general protein inactivation mechanism of the DBD. The antibody’s heavy and light chains linked by disulfide bonds dissociated after plasma exposure. Based on their ability to inactivate proteins by oxidation of sulfur-containing amino acids and over-oxidation of disulfide bonds, DBD devices present a viable option for inactivating undesired or hazardous proteins on heat or solvent-sensitive surfaces. [ABSTRACT FROM AUTHOR]

The incorrect surface density of bacteria (4 x 106 cm-2) on the agar plate was given in the right column, line 16, on page 3 in section 3 'Substrate preparation'. The correct surface coverage was 2.2 x 103 cm-2. This surface coverage was selected to obtain a homogeneous surface coverage after 18 hours of incubation at 37 degC. The term 'monolayer surface coverage' in the same section is used to stress the fact that there is no multilayer of bacteria during the treatment and that the shadowing effects can be neglected. However, the surface is not fully covered by one continuous layer of bacteria. This error and ambiguity in the use of the term 'monolayer surface coverage' does not affect the interpretation of the results and conclusions in the article. Additionally, the names of Volker Schulz-von der Gathen and Nikolas Knake have been misspelled in the 'Acknowledgments'. The authors apologize for any inconvenience and confusion they may have caused. [ABSTRACT FROM AUTHOR]