Molybdenum cofactor-dependent resistance to N-hydroxylated base analogs in Escherichia coli is independent of MobA function

Abstract

Lack of molybdenum cofactor (MoCo) in Escherichia coli and related microorganisms was found to cause hypersensitivity to certain N-hydroxylated base analogs, such as HAP (6-N-hydroxylaminopurine). This observation has lead to a previous proposal that E. coli contains a molybdoenzyme capable of detoxifying such N-hydroxylated analogs. Here, we show that, unexpectedly, deletion of all known or putative molybdoenzymes in E. coli failed to reveal any base-analog sensitivity, suggesting that a novel type of MoCo-dependent activity is involved. Further, we establish that protection against the analogs does not require the common molybdopterin guanine-dinucleotide (MGD) form of the cofactor, but instead the guanosine monophosphate (GMP)-free version of MoCo (MPT) is sufficient.

Fig. 1

(A) MoCo biosynthesis in E. coli and HAP sensitivity of strains blocked in the indicated steps in the MGD synthesis pathway. Deletions of indicated genes were created and transferred to strain NR10836 [17] as indicated in text. 50 μg of HAP was spotted onto the center of each plate as described [17]. (B) Chlorate resistance of the MoCo-deficient strains (see Materials and Methods). The combined (A) and (B) demonstrate that a mobA mutant is resistant to HAP while being defective in MGD evidenced by its chlorate resistance.