Structure and Function of CinD (YtjD) ofLactococcus lactis, a Copper-Induced Nitroreductase Involved in Defense against Oxidative Stress

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Abstract
InLactococcus lactisIL1403, 14 genes are under the control of the copper-inducible CopR repressor. This so-called CopR regulon encompasses the CopR regulator, two putative CPx-type copper ATPases, a copper chaperone, and 10 additional genes of unknown function. We addressed here the function of one of these genes,ytjD, which we renamedcinD( c opper- i nduced n itroreductase). Copper, cadmium, and silver inducedcinD in vivo, as shown by real-time quantitative PCR. A knockout mutant ofcinDwas more sensitive to oxidative stress exerted by 4-nitroquinoline-N-oxide and copper. Purified CinD is a flavoprotein and reduced 2,6-dichlorophenolindophenol and 4-nitroquinoline-N-oxide withkcatvalues of 27 and 11 s−1, respectively, using NADH as a reductant. CinD also exhibited significant catalase activityin vitro. The X-ray structure of CinD was resolved at 1.35 Å and resembles those of other nitroreductases. CinD is thus a nitroreductase which can protectL. lactisagainst oxidative stress that could be exerted by nitroaromatic compounds and copper.

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