Reductive elimination pathway for homocysteine to methionine conversion in cobalamin-dependent methionine synthase

Infection with Helicobacter pylori may predispose to atherosclerosis: role of inflammation and thickening of intima-media of carotid arteries

Atherosclerosis is a major instigator of cardiovascular disease (CVD) and a main cause of global morbidity and mortality. The high prevalence of CVD calls for urgent attention to possible preventive measures in order to curb its incidence. Traditional risk factors of atherosclerosis, like age, smoking, diabetes mellitus, dyslipidemia, hypertension and chronic inflammation, are under extensive investigation. However, these only account for around 50% of the etiology of atherosclerosis, mandating a search for different or overlooked risk factors. In this regard, chronic infections, by Helicobacter pylori for instance, are a primary candidate. H. pylori colonizes the gut and contributes to several gastrointestinal diseases, but, recently, the potential involvement of this bacterium in extra-gastric diseases including CVD has been under the spotlight. Indeed, H. pylori infection appears to stimulate foam cell formation as well as chronic immune responses that could upregulate key inflammatory mediators including cytokines, C-reactive protein, and lipoproteins. These factors are involved in the thickening of intima-media of carotid arteries (CIMT), a hallmark of atherosclerosis. Interestingly, H. pylori infection was found to increase (CIMT), which along with other evidence, could implicate H. pylori in the pathogenesis of atherosclerosis. Nevertheless, the involvement of H. pylori in CVD and atherosclerosis remains controversial as several studies report no connection between H. pylori and atherosclerosis. This review examines and critically discusses the evidence that argues for a potential role of this bacterium in atherogenesis. However, additional basic and clinical research studies are warranted to convincingly establish the association between H. pylori and atherosclerosis.

Methyl transfer reactions catalyzed by cobalamin-dependent enzymes: Insight from molecular docking

Methyl transfer reactions, mediated by methyltransferases (MeTrs), such as methionine synthase (MetH) or monomethylamine: CoM (MtmBC), constitute one of the most important classes of vitamin B₁₂-dependent reactions. The challenge in exploring the catalytic function of MeTrs is related to their modular structure. From the crystallographic point of view, the structure of each subunit has been determined, but there is a lack of understanding of how each subunit interacts with each other. So far, theoretical studies of methyl group transfer were carried out for the structural models of the active site of each subunit. However, those studies do not include the effect of the enzymatic environment, which is crucial for a comprehensive understanding of enzyme-mediated methyl transfer reactions. Herein, to explore how two subunits interact with each other and how the methyl transfer reaction is catalyzed by MeTrs, molecular docking of the functional units of MetH and MtmBC was carried out. Along with the interactions of the functional units, the reaction coordinates, including the Co-C bond distance for methylation of cob(I)alamin (Co^ICbl) and the C-S bond distance in demethylation reaction of cob(III)alamin (Co^IIICbl), were considered. The functional groups should be arranged so that there is an appropriate distance to transfer a methyl group and present results indicate that steric interactions can limit the number of potential arrangements. This calls into question the possibility of S_N2-type mechanism previously proposed for MeTrs. Further, it leads to the conclusion that the methyl transfer reaction involves some spatial changes of modules suggesting an alternate radical-based pathway for MeTrs-mediated methyl transfer reactions. The calculations also showed that changes in torsion angles induce a change in reaction coordinates, namely Co-C and C-S bond distances, for the methylation and demethylation reactions catalyzed both by MetH and MtmBC.

Intraprotein transmethylation via a CH3–Co(iii) species in myoglobin reconstituted with a cobalt corrinoid complex

A cobalt corrinoid complex bound in the myoglobin heme pocket demonstrates the formation of a CH₃–Co(iii) bond and subsequent transmethylation.

Co-C dissociation of adenosylcobalamin (coenzyme B12): role of dispersion, induction effects, solvent polarity, and relativistic and thermal corrections

Quantum-chemical cluster modeling is challenged in the limit of large, soft systems by the effects of dispersion and solvent, and well as other physical interactions. Adenosylcobalamin (AdoCbl, coenzyme B12), as one of the most complex cofactors in life, constitutes such a challenge. The cleavage of its unique organometallic Co-C bond has inspired multiple studies of this cofactor. This paper reports the fully relaxed potential energy surface of Co-C cleavage of AdoCbl, including for the first time all side-chain interactions with the dissociating Ado group. Various methods and corrections for dispersion, relativistic effects, solvent polarity, basis set superposition error, and thermal and vibrational effects were investigated, totaling more than 550 single-point energies for the large model. The results show immense variability depending on method, including solvation, functional type, and dispersion, challenging the conceived accuracy of methods used for such systems. In particular, B3LYP-D3 seems to severely underestimate the Co-C bond strength, consistent with previous results, and BP86 remains accurate for cobalamins when dispersion interactions are accounted for.