Very low
nitrogen concentration is a critical limitation in the oligotrophic oceans inhabited by the cyanobacterium Prochlorococccus, one of the main primary producers on Earth. It is well known that
nitrogen starvation affects redox homeostasis in cells. We have studied the effect of
nitrogen starvation on the
thiol redox
proteome in the Prochlorococcus sp. SS120 strain, by using shotgun proteomic techniques to map the
cysteine modified in each case and to quantify the ratio of reversibly oxidized/reduced species. We identified a number of
proteins showing modified cysteines only under either control or N-
starvation, including
isocitrate dehydrogenase and
ribulose phosphate 3-epimerase. We detected other key
enzymes, such as
glutamine synthetase, transporters and
transaminases, showing that
nitrogen-related pathways were deeply affected by
nitrogen starvation. Reversibly oxidized cysteines were also detected in
proteins of other important metabolic pathways, such as photosynthesis,
phosphorus metabolism,
ATP synthesis and
nucleic acids metabolism. Our results demonstrate a wide effect of
nitrogen limitation on the redox status of the Prochlorococcus
proteome, suggesting that besides previously reported transcriptional changes, this cyanobacterium responds with post-translational redox changes to the lack of
nitrogen in its environment.