Coenzyme specificity of para-hydroxybenzoate hydroxylase and related flavoprotein monooxygenases

What is it about?

p-Hydroxybenzoate hydroxylase (PHBH) and related group A flavoprotein monooxygenases lack a canonical NAD(P)H-binding domain and the way they interact with the pyridine nucleotide coenzyme is shrouded in mystery. Here, we report a phylogenetic analysis, which shows that PHBHs group into three clades consisting of NADPH-specific, NAD(P)H-dependent and NADH-preferring enzymes. The latter proteins frequently occur in Actinobacteria. To validate the results, we produced several putative PHBHs in Escherichia coli and confirmed their predicted coenzyme preferences. Based on phylogeny, protein energy profiling and lifestyle of PHBH harboring bacteria we propose that the coenzyme specificity of PHBH emerged through adaptive evolution and that the NADH-preferring enzymes are the older versions of PHBH. Structural comparison and distance tree analysis of group A flavoprotein monooxygenases indicate that a similar protein segment as being responsible for the coenzyme specificity of PHBH is involved in determining the coenzyme specificity of the other group A members.

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Why is it important?

Understanding the coenzyme preference of flavin-dependent aromatic hydroxylases is intriguing from a structural point of view and crucial for their use in biocatalysis.

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