Proteomics of vitamin B12 processing

Abstract

The causes of cobalamin (B 12 , Cbl) deficiency are multifactorial. Whether nutritional due to poor dietary intake, or functional due to impairments in absorption or intracellular processing and trafficking events, the major symptoms of Cbl deficiency include megaloblastic anemia, neurological deterioration and in extreme cases, failure to thrive and death. The common biomarkers of Cbl deficiency (hyperhomocysteinemia and methylmalonic acidemia) are extremely valuable diagnostic indicators of the condition, but little is known about the changes that occur at the protein level. A mechanistic explanation bridging the physiological changes associated with functional B 12 deficiency with its intracellular processers and carriers is lacking. In this article, we will cover the effects of B 12 deficiency in a cblC -disrupted background (also referred to as MMACHC) as a model of functional Cbl deficiency. As will be shown, major protein changes involve the cytoskeleton, the neurological system as well as signaling and detoxification pathways. Supplementation of cultured MMACHC-mutant cells with hydroxocobalamin (HOCbl) failed to restore these variants to the normal phenotype, suggesting that a defective Cbl processing pathway produces irreversible changes at the protein level.

Inherited disorders of cobalamin metabolism disrupt nucleocytoplasmic transport of mRNA through impaired methylation/phosphorylation of ELAVL1/HuR

“…Cbl impaired metabolism of the cultured TO neuroblastoma cells caused endoplasmic reticulum (ER) stress downstream of reduced SIRT1 expression (5). The latter result is in line with the previous proteomic results from fibroblasts with inborn errors of Cbl metabolism; these cells show large-scale changes in protein expression in ER and in ubiquitin-proteasome system with UPR (unfolded protein response) and anti-oxidative stress functions (15). …”

Peroxisome Proliferator-Activated Receptor Activation is Associated with Altered Plasma One-Carbon Metabolites and B-Vitamin Status in Rats

“…One potential mechanism could be inhibition of the methylmalonic aciduria combined with homocystinuria type C (MMACHC) protein. MMACHC is a flavoprotein responsible for making free cobalamin available for cofactor synthesis [ 60 ], and lower availability of vitamin B2 may thus reduce MMACHC function. Also, MMACHC is dependent on glutathione transferase activity [ 61 ], linking cobalamin metabolism to the transsulfuration pathway, which is a substantial source of cysteine for glutathione synthesis [ 62 ].…”

Transcellular transport of cobalamin in aortic endothelial cells

“…Most of the endocytosed [ 57 Co]-CNCbl-TC partitioned into 3 possible fates ( Fig. 7): 1) exocytosis yielding protein-free [ 57 Co]-CNCbl, 2) intracellular retention of [ 57 Co]-CNCbl without chemical modification, and 3) intracellular processing of [ 57 Co]-CNCbl by the enzyme MMACHC/cblC (26,32) with subsequent conversion to [ 57 Co]-MeCbl and [ 57 Co]-AdoCbl by MS and MCM. That is consistent with previous observations that the major reservoirs of Cbl in cells are the enzymes MS and MCM.…”

“…Cells take up holo-TC via endocytosis, mediated by the TC receptor (TCblR/CD320) (13)(14)(15)(16)(17)(18)(19)(20)(21).The holo-TC complex is then degraded in lysosomes, and free Cbl is transported into the cytosol by lysosomal proteins Cbl complementation group F (cblF) (22)(23)(24) and cblJ (25,26), which render the micronutrient available for processing and trafficking by the methylmalonic aciduria and homocystinuria type C (MMACHC/cblC) (27,28) and methylmalonic aciduria type D and homocystinuria (MMADHC/cblD) (29)(30)(31) proteins, respectively. An additional group of proteins deliver the micronutrient to its final intracellular destinations, cytosolic MS and mitochondrial MCM (27,32,33). Cbl can also be mobilized across cellular compartments by transcellular transport.…”