Biochemical and Physiological Studies of a Novel Nudix Hydrolase, NuhA, in Cyanobacteria

Abstract

The Nudix hydrolase is a family of proteins that hydrolyzes nucleic acid derivatives, such as (d)NTP, NADH and ADP-ribose. We cloned the nuhA gene encoding a novel Nudix hydrolase, NuhA, in Synechococcus sp. PCC 7002 that hydrolyzes ADP-ribose specifically.
The NuhA protein contained a catalytic Nudix domain in the N-terminal region and an uncharacterized domain termed PfamB-3375 in the C-terminal region. The mutated NuhA with a trancated PfamB-3375 domain showed a higher K_m than the wild-type NuhA. Moreover, the mutated protein failed to form a hexamer, which was characteristic of NuhA.
We inactivated the nuhA gene to examine the role of NuhA in vivo. The ΔnuhA cells grew while forming the aggregation of cells in low-CO₂ conditions. However, the aggregation of ΔnuhA cells was prevented in high-CO₂ conditions. It appears that enough supply of CO₂ mitigates the harmful effects caused by the accumulation of ADP-ribose.