Conversion of Cobinamide into Adenosylcobamide in Bacteria and Archaea

Adenosylcobalamin (AdoCbl, also known as [aka] coenzyme B 12 ) is the most complex coenzyme known, and its biosynthesis requires a great deal of genetic information (Fig. 1) (61).The core of AdoCbl is a cobalt-containing cyclic tetrapyrrolidine/ pyrroline known as the corrin ring.The latter is synthesized only by prokaryotes via either of two pathways, the aerobic or anaerobic pathway, which differ in several important ways, but most notably in the timing of cobalt insertion (early in the anaerobic pathway, late in the aerobic pathway) and the type of cobaltochelatase used by each pathway (reviewed in references 5, 49, and 61).Unlike other members of the metal-containing cyclic tetrapyrroles, AdoCbl has upper and lower ligands, and in prokaryotes such as Salmonella enterica serovar Typhimurium (hereafter serovar Typhimurium), these ligands are attached to the corrin ring under aerobic or anaerobic conditions (21,28).Recently, C. A. Roessner and A. I. Scott published a minireview on the topic of anaerobic de novo corrin ring biosynthesis which fine-tuned our understanding of the assembly of the core of Cbl (46).It is only fitting to offer the readership of the journal a minireview of what has been learned about other important aspects of coenzyme B 12 synthesis in bacteria and archaea.Unfortunately, the nomenclature for coenzyme B 12 is complex.The rules for naming complete molecules and precursors have been published by the Commission on Biochemical Nomenclature (CBN) of the International Union of Pure and Applied Chemistry (IUPAC) and revised by the International Union of Biochemistry (IUB) (2, 3).For the reader's benefit, I define below terminology used in this minireview.Corrinoids.Molecules containing the cobalt-containing cyclic tetrapyrrole known as the corrin ring.Incomplete corrinoids.Corrinoids lacking the lower (Co␣) axial ligand base.Cobamide (Cba).A complete corrinoid, that is, a corrinoid containing the nucleotide loop.The name of the Cba depends on the nature of the lower ligand.Cobalamin (Cbl).The Cba whose lower (Co␣) ligand base is 5,6-dimethylbenzimidazole (DMB).Adenosylcobamide (AdoCba).The coenzymic form of a Cba whose lower (Co␣) ligand is not DMB.PseudoAdoCba.The coenzymic form of AdoCba with adenine as the lower (Co␣) ligand.Vitamin B 12 , or cyanocobalamin.Cbl with a cyano group as the upper (Co␤) ligand.