Protection of aquo/hydroxocobalamin from reduced glutathione by a B_(12) trafficking chaperone
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We identified a bovine B_(12) trafficking chaperone bCblC in Bos taurus that showed 88% amino acid sequence identity with a human homologue. The protein bCblC was purified from E. coli by over-expression of the encoding gene. bCblC bound cyanocobalamin (CNCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) in the base-off states and eliminated the upper axial ligands forming aquo/hydroxocobalamin (OH₂/OHCbl) under aerobic conditions. A transition of OH₂/OHCbl was induced upon binding to bCblC. Interestingly,bCblC-bound OH₂/OHCbl did not react with reduced glutathione (GSH), while the reaction of free OH₂/OHCbl with GSH resulted in the formation of glutathionylcobalamin (GSCbl)and glutathione disulfide (GSSG). Furthermore we found that bCblC eliminates the GSH ligand of GSCbl forming OH₂/OHCbl. The results demonstrated that bCblC is a B12 trafficking chaperone that binds cobalamins and protects OH₂/OHCbl from GSH, which could be oxidized to GSSG by free OH₂/OHCbl. [BMB reports 2011; 44(3): 170-175]
Abstract
We identified a bovine B_(12) trafficking chaperone bCblC in Bos taurus that showed 88% amino acid sequence identity with a human homologue. The protein bCblC was purified from E. coli by over-expression of the encoding gene. bCblC bound cyanocobalamin (CNCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) in the base-off states and eliminated the upper axial ligands forming aquo/hydroxocobalamin (OH₂/OHCbl) under aerobic conditions. A transition of OH₂/OHCbl was induced upon binding to bCblC. Interestingly,bCblC-bound OH₂/OHCbl did not react with reduced glutathione (GSH), while the reaction of free OH₂/OHCbl with GSH resulted in the formation of glutathionylcobalamin (GSCbl)and glutathione disulfide (GSSG). Furthermore we found that bCblC eliminates the GSH ligand of GSCbl forming OH₂/OHCbl. The results demonstrated that bCblC is a B12 trafficking chaperone that binds cobalamins and protects OH₂/OHCbl from GSH, which could be oxidized to GSSG by free OH₂/OHCbl. [BMB reports 2011; 44(3): 170-175]
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