Characterization of the complex between native and reduced bovine serum albumin with aquacobalamin and evidence of dual tetrapyrrole binding

Abstract

Serum albumin binds to a variety of endogenous ligands and drugs. Human serum albumin (HSA) binds to heme via hydrophobic interactions and axial coordination of the iron center by protein residue Tyr161. Human serum albumin binds to another tetrapyrrole, cobalamin (Cbl), but the structural and functional properties of this complex are poorly understood. Herein, we investigate the reaction between aquacobalamin (HOCbl) and bovine serum albumin (BSA, the bovine counterpart of HSA) using Ultraviolet-Visible and fluorescent spectroscopy, and electron paramagnetic resonance. The reaction between HOCbl and BSA led to the formation of a BSA-Cbl(III) complex consistent with N-axial ligation (amino). Prior to the formation of this complex, the reactants participate in an additional binding event that has been examined by fluorescence spectroscopy. Binding of BSA to Cbl(III) reduced complex formation between the bound cobalamin and free cyanide to form cyanocobalamin (CNCbl), suggesting that the β-axial position of the cobalamin may be occupied by an amino acid residue from the protein. Reaction of BSA containing reduced disulfide bonds with HOCbl produces cob(II)alamin and disulfide with intermediate formation of thiolate Cbl(III)-BSA complex and its decomposition. Finally, in vitro studies showed that cobalamin binds to BSA only in the presence of an excess of protein, which is in contrast to heme binding to BSA that involves a 1:1 stoichiometry. In vitro formation of BSA-Cbl(III) complex does not preclude subsequent heme binding, which occurs without displacement of HOCbl bound to BSA. These data suggest that the two tetrapyrroles interact with BSA in different binding pockets.

Elevated Plasma Vitamin B12 in Patients with Hepatic Glycogen Storage Diseases

“…Therefore, it is currently unknown whether GSD patients with highly elevated vitamin B 12 have a saturated cobalamin binding capacity of its authentic transport proteins. If so, excess vitamin B 12 might bind to non-dedicated proteins such as albumin [ 47 , 48 , 49 , 50 ] and the recently described immunocomplexes [ 51 , 52 , 53 ]. The biological activity of these protein complexes of vitamin B 12 is unknown and currently under investigation.…”

High Reactivity of Supermolecular Nanoentities of a Vitamin B12 Derivative in Langmuir–Schaefer Films Toward Gaseous Toxins

“…Aquacobalamin (H 2 OCbl) is a well-known cyanide antidote due to the high affinity of the Co­(III) ion toward this toxin . However, the reaction between H 2 OCbl and CN – has some features that can decrease its efficacy as an antidote, i.e., it is relatively slow in neutral aqueous solutions, and H 2 OCbl forms complexes with biological ligands and proteins , that leads to inhibition of the CN – binding. In contrast to H 2 OCbl, cobinamides (Cbis), nucleotide-free derivatives of Cbls, react with CN – significantly more rapidly, and some Cbi species retain this reactivity in the presence of competitive ligands. , Moreover, Cbis possesses higher water solubility and can be introduced via intramuscular injection .…”

Influence of Proteins on the Interaction Between Sodium Selenite and Sulfur-Containing Reductants

“…3). Очевидно, этот эффект связан с наличием в альбумине групп, способных восстанавливаться и образовывать соединение, взаимодействующее с селенитом; таковыми могут быть присутствующие в БСА цистиновые фрагменты [18]. Были проведены опыты по восстановлению селенита гидроксиметансульфинатом в присутствии L-цистина и его селеносодержащего аналогаселено-L-цистина.…”