Allosteric Regulation of Oligomerization by a B Trafficking G-Protein Is Corrupted in Methylmalonic Aciduria.

Allosteric regulation of methylmalonyl-CoA mutase (MCM) by the G-protein chaperone CblA is transduced via three "switch" elements that gate the movement of the B cofactor to and from MCM. Mutations in CblA and MCM cause hereditary methylmalonic aciduria. Unlike the bacterial orthologs used previously to model disease-causing mutations, human MCM and CblA exhibit a complex pattern of regulation that involves interconverting oligomers, which are differentially sensitive to the presence of GTP versus GDP.

Sacrificial Cobalt-Carbon Bond Homolysis in Coenzyme B as a Cofactor Conservation Strategy.

A sophisticated intracellular trafficking pathway in humans is used to tailor vitamin B into its active cofactor forms, and to deliver it to two known B-dependent enzymes. Herein, we report an unexpected strategy for cellular retention of B, an essential and reactive cofactor. If methylmalonyl-CoA mutase is unavailable to accept the coenzyme B product of adenosyltransferase, the latter catalyzes homolytic scission of the cobalt-carbon bond in an unconventional reversal of the nucleophilic displacement reaction that was used to make it.

Functional Role of Solvent Entropy and Conformational Entropy of Metal Binding in a Dynamically Driven Allosteric System.

Allostery is a regulatory phenomenon whereby ligand binding to one site influences the binding of the same or a different ligand to another site on a macromolecule. The physical origins of allosteric regulation remain under intense investigation. In general terms, ligand-induced structural changes, perturbations of residue-specific dynamics, and surrounding solvent molecules all potentially contribute to the global energetics of allostery.

The Human Knockout Gene CLYBL Connects Itaconate to Vitamin B.

CLYBL encodes a ubiquitously expressed mitochondrial enzyme, conserved across all vertebrates, whose cellular activity and pathway assignment are unknown. Its homozygous loss is tolerated in seemingly healthy individuals, with reduced circulating B levels being the only and consistent phenotype reported to date. Here, by combining enzymology, structural biology, and activity-based metabolomics, we report that CLYBL operates as a citramalyl-CoA lyase in mammalian cells.