An Enzyme Containing the Conserved Domain of Unknown Function DUF62 Acts as a Stereoselective (R_s,S_c)‐S‐Adenosylmethionine Hydrolase

Abstract

Homochirality is a signature of biological systems. The essential and ubiquitous cofactor S‐adenosyl‐l‐methionine (SAM) is synthesized in cells from adenosine triphosphate and l‐methionine to yield exclusively the (S,S)‐SAM diastereomer. (S,S)‐SAM plays a crucial role as the primary methyl donor in transmethylation reactions important to the development and homeostasis of all organisms from bacteria to humans. However, (S,S)‐SAM slowly racemizes at the sulfonium center to yield the inactive (R,S)‐SAM, which can inhibit methyltransferases. Control of SAM homochirality has been shown to involve homocysteine S‐methyltransferases in plants, insects, worms, yeast, and in ∼18 % of bacteria. Herein, we show that a recombinant protein containing a domain of unknown function (DUF62) from the actinomycete bacterium Salinispora tropica functions as a stereoselective (R,S)‐SAM hydrolase (adenosine‐forming). DUF62 proteins are encoded in the genomes of 21 % of bacteria and 42 % of archaea and potentially represent a novel mechanism to remediate SAM damage.

Biochemical and Structural Studies of the Carminomycin 4-O-Methyltransferase DnrK

“…Corresponding control reactions lacking DnrK or AdoMet led to no product. As commercially sourced AdoMet stereochemistry and stability is variable, ,, turnover in a model reaction (conversion of 1 to 1a ) with commercially sourced AdoMet (NEB) was compared to AdoMet generated via methionine adenosyltransferase (MAT)-catalyzed conversion (which affords a single AdoMet stereoisomer from ATP and l -methionine) and found to be identical. Thus, commercially sourced AdoMet was used for all assays described.…”

S-Adenosylmethionine: more than just a methyl donor

“…101 Although the biological function of hydroxide adenosyltransferases is not as obvious as their halogenase counterparts, recent research identied a DUF62containing protein, StDUF62, catalyzing the stereoselective hydrolysis of the non-native (R,S)-SAM (43), which is a stereoisomer that equilibrates with biological (S,S)-SAM (1) upon racemization of the sulfonium. 106 This hints at a role played by DUF62 proteins in preventing in vivo accumulation of the nonbiological SAM diastereomer.…”

Molecular Insights into Converting Hydroxide Adenosyltransferase into Halogenase

“…40 These two types of enzymes belong to the Duf-62 superfamily and share similar protein structures. 40,46,47 However, they catalyze different reactions (Scheme 1). The molecular basis for the specific recognition of halide ions or water has not been determined.…”

“…SAM hydroxide adenosyltransferase (HATase) is a SAM-dependent hydroxylase with high sequence homology to chlorinase (Scheme ). These two types of enzymes belong to the Duf-62 superfamily and share similar protein structures. ,, However, they catalyze different reactions (Scheme ). The molecular basis for the specific recognition of halide ions or water has not been determined.…”