Methylglyoxal detoxification by an aldo-keto reductase in the cyanobacterium Synechococcus sp. PCC 7002.

Aldo-keto reductases (AKRs) are a superfamily of enzymes that reduce aldehydes and ketones, and have a broad range of substrates. An AKR gene, sakR1, was identified in the cyanobacterium Synechococcus sp. PCC 7002. A mutant strain with sakR1 inactivated was sensitive to glycerol, a carbon source that can support heterotrophic growth of Synechococcus sp. PCC 7002. It was found that the sakR1 null mutant accumulated more toxic methylglyoxal than the wild-type when glycerol was added to growth medium, suggesting that SakR1 is involved in the detoxification of methylglyoxal, a highly toxic metabolite that can damage cellular macromolecules. Enzymic analysis of recombinant SakR1 protein showed that it can efficiently reduce methylglyoxal with NADPH. Based on immunoblotting, SakR1 was not upregulated at an increased cellular methylglyoxal concentration. A pH-dependent enzyme-activity profile suggested that SakR1 activity could be regulated by cellular pH in Synechococcus sp. PCC 7002. The broad substrate specificity of SakR1 implies that SakR1 could play other roles in cellular metabolism.