Structural and functional analysis of an l ‐serine O‐ phosphate decarboxylase involved in norcobamide biosynthesis

Structural diversity of natural cobamides (Cbas, B 12 vitamers) is limited to the nucleotide loop. The loop is connected to the cobalt‐containing corrin ring via an ( R )‐1‐aminopropan‐2‐ol O ‐2‐phosphate (AP‐P) linker moiety. AP‐P is produced by the l ‐threonine O ‐3‐phosphate ( l ‐Thr‐P) decarboxylase CobD. Here, the CobD homolog SMUL_1544 of the organohalide‐respiring epsilonproteobacterium Sulfurospirillum multivorans was characterized as a decarboxylase that produces ethanolamine O ‐phosphate (EA‐P) from l ‐serine O‐ phosphate ( l ‐Ser‐P). EA‐P is assumed to serve as precursor of the linker moiety of norcobamides that function as cofactors in the respiratory reductive dehalogenase. SMUL_1544 ( Sm CobD) is a pyridoxal‐5′‐phosphate (PLP)‐containing enzyme. The structural analysis of the Sm CobD apoprotein combined with the characterization of truncated mutant proteins uncovered a role of the Sm CobD N‐terminus in efficient l ‐Ser‐P conversion.