Abstract
Acinetobacter sp. Ver3 is a polyextremophilic strain characterized by a high tolerance to radiation and pro-oxidants. The Ver3 genome comprises the sodB and sodC genes encoding an iron (AV3SodB) and a copper/zinc superoxide dismutase (AV3SodC), respectively; however, the specific role(s) of these genes has remained elusive. We show that the expression of sodB remained unaltered in different oxidative stress conditions whereas sodC was up-regulated in the presence of blue light. Besides, we studied the changes in the in vitro activity of each SOD enzyme in response to diverse agents and solved the crystal structure of AV3SodB at 1.34 Å, one of the highest resolutions achieved for a SOD. Cell fractionation studies interestingly revealed that AV3SodB is located in the cytosol whereas AV3SodC is also found in the periplasm. Consistently, a bioinformatic analysis of the genomes of 53 Acinetobacter species pointed out the presence of at least one SOD type in each compartment, suggesting that these enzymes are separately required to cope with oxidative stress. Surprisingly, AV3SodC was found in an active state also in outer membrane vesicles, probably exerting a protective role. Overall, our multidisciplinary approach highlights the relevance of SOD enzymes when Acinetobacterspp. are confronted with oxidizing agents.
Highlights
Since the CuZnSOD from A. baumannii ATCC 17978 has been detected in OMVs32, we investigated whether this was the case for AV3SodC
superoxide dismutases (SODs) enzymes are ubiquitous in biology, so understanding the principles that govern their kinetic parameters, the use of metal cofactors and the subcellular localization has diverse implications
SODs are part of the bacterial defence against oxidative stress and, by detoxifying the superoxide produced by the mammalian immune system in response to infection, they play a crucial role in pathogenesis
Summary
The thermostability of recombinant AV3SodB and AV3SodC-p was investigated by pre-incubating the enzymes at different temperatures followed by measurements of the residual activity (Fig. 3c,d). Treatment with inhibitors showed mixed effects on enzyme activity, with AV3SodB being altered mainly by SDS and ethanol, whereas AV3SodC-p was affected by EDTA and guanidine hydrochloride.
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