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An Interprotein Co-S Coordination Complex in the B₁₂-Trafficking Pathway.

ABSTRACT: The CblC and CblD chaperones are involved in early steps in the cobalamin trafficking pathway. Cobalamin derivatives entering the cytoplasm are converted by CblC to a common cob(II)alamin intermediate via glutathione-dependent alkyltransferase or reductive elimination activities. Cob(II)alamin is subsequently converted to one of two biologically active alkylcobalamins by downstream chaperones. The function of CblD has been elusive although it is known to form a complex with CblC under certain conditions. Here, we report that CblD provides a sulfur ligand to cob(II)alamin bound to CblC, forming an interprotein coordination complex that rapidly oxidizes to thiolato-cob(III)alamin. Cysteine scanning mutagenesis and EPR spectroscopy identified Cys-261 on CblD as the sulfur donor. The unusual interprotein Co-S bond was characterized by X-ray absorption spectroscopy and visualized in the crystal structure of the human CblD thiolato-cob(III)alamin complex. Our study provides insights into how cobalamin coordination chemistry could be utilized for cofactor translocation in the trafficking pathway.

SUBMITTER: Li Z

PROVIDER: S-EPMC7530128 | biostudies-literature | 2020 Sep

REPOSITORIES: biostudies-literature

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An Interprotein Co-S Coordination Complex in the B<sub>12</sub>-Trafficking Pathway.

Li Zhu Z Mascarenhas Romila R Twahir Umar T UT Kallon Albert A Deb Aniruddha A Yaw Madeline M Penner-Hahn James J Koutmos Markos M Warncke Kurt K Banerjee Ruma R

Journal of the American Chemical Society 20200914 38

The CblC and CblD chaperones are involved in early steps in the cobalamin trafficking pathway. Cobalamin derivatives entering the cytoplasm are converted by CblC to a common cob(II)alamin intermediate via glutathione-dependent alkyltransferase or reductive elimination activities. Cob(II)alamin is subsequently converted to one of two biologically active alkylcobalamins by downstream chaperones. The function of CblD has been elusive although it is known to form a complex with CblC under certain co ...[more]

PMID: 32871076

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Project description:Metals are partners for an estimated one-third of the proteome and vary in complexity from mononuclear centers to organometallic cofactors. Vitamin B12 or cobalamin represents the epitome of this complexity and is the product of an assembly line comprising some 30 enzymes. Unable to biosynthesize cobalamin, mammals rely on dietary provision of this essential cofactor, which is needed by just two enzymes, one each in the cytoplasm (methionine synthase) and the mitochondrion (methylmalonyl-CoA mutase). Brilliant clinical genetics studies on patients with inborn errors of cobalamin metabolism spanning several decades had identified at least seven genetic loci in addition to the two encoding B12 enzymes. While cells are known to house a cadre of chaperones dedicated to metal trafficking pathways that contain metal reactivity and confer targeting specificity, the seemingly supernumerary chaperones in the B12 pathway had raised obvious questions as to the rationale for their existence.With the discovery of the genes underlying cobalamin disorders, our laboratory has been at the forefront of ascribing functions to B12 chaperones and elucidating the intricate redox-linked coordination chemistry and protein-linked cofactor conformational dynamics that orchestrate the processing and translocation of cargo along the trafficking pathway. These studies have uncovered novel chemistry that exploits the innate chemical versatility of alkylcobalamins, i.e., the ability to form and dismantle the cobalt-carbon bond using homolytic or heterolytic chemistry. In addition, they have revealed the practical utility of the dimethylbenzimidazole tail, an appendage unique to cobalamins and absent in the structural cousins, porphyrin, chlorin, and corphin, as an instrument for facilitating cofactor transfer between active sites.In this Account, we navigate the chemistry of the B12 trafficking pathway from its point of entry into cells, through lysosomes, and into the cytoplasm, where incoming cobalamin derivatives with a diversity of upper ligands are denuded by the β-ligand transferase activity of CblC to the common cob(II)alamin intermediate. The broad reaction and lax substrate specificity of CblC also enables conversion of cyanocobalamin (technically, vitamin B12, i.e., the form of the cofactor in one-a-day supplements), to cob(II)alamin. CblD then hitches up with CblC via a unique Co-sulfur bond to cob(II)alamin at a bifurcation point, leading to the cytoplasmic methylcobalamin or mitochondrial 5'-deoxyadenosylcobalamin branch. Mutations at loci upstream of the junction point typically affect both branches, leading to homocystinuria and methylmalonic aciduria, whereas mutations in downstream loci lead to one or the other disease. Elucidation of the biochemical penalties associated with individual mutations is providing molecular insights into the clinical data and, in some instances, identifying which cobalamin derivative(s) might be therapeutically beneficial.Our studies on B12 trafficking are revealing strategies for cofactor sequestration and mobilization from low- to high-affinity and low- to high-coordination-number sites, which in turn are regulated by protein dynamics that constructs ergonomic cofactor binding pockets. While these B12 lessons might be broadly relevant to other metal trafficking pathways, much remains to be learned. This Account concludes by identifying some of the major gaps and challenges that are needed to complete our understanding of B12 trafficking.

Project description:The reaction of Co(NCS)2 with urotropine in ethanol leads to the formation of two different compounds, namely, bis-(ethanol-κO)bis-(hexa-methyl-ene-tetra-mine-κN)bis-(thio-cyanato-κN)cobalt(II)-di-aqua-κ 2O-bis-(hexa-methyl-ene-tetra-mine-κN)bis-(thio-cyanato-κN)cobalt(II)-ethanol-hexa-methyl-ene-tetra-mine (1.2/0.8/1.6/4), [Co(NCS)2(C6H12N4)2(C2H6O)2]1.2·[Co(NCS)2(C6H12N4)2(H2O)2]0.8·1.6C2H6O·4C6H12N4, 1, and tris-(ethanol-κO)(hexa-methyl-ene-tetra-mine-κN)bis(thio-cyanato-κN)cobalt(II), [Co(NCS)2(C6H12N4)(C2H6O)3], 2. In the crystal structure of compound 1, two crystallographically independent discrete complexes are observed that are located on centres of inversion. In one of them, the Co cation is octa-hedrally coordinated to two terminal N-bonded thio-cyanate anions, two urotropine ligands and two ethanol mol-ecules, whereas in the second complex 80% of the coordinating ethanol is exchanged by water. Formally, compound 1 is a mixture of two different complexes, i.e. di-aqua-dithio-cyanato-bis-(urotropine)cobalt(II) and di-ethano-ldi-thio-cyanato-bis-(uro-trop-ine)cobalt(II), that contain additional ethanol and urotropine solvate mol-ecules leading to an overall composition of [Co(NCS)2(urotropine)2(ethanol)1.2(H2O)0.8·0.8ethanol·4urotropine. Both discrete complexes are linked by inter-molecular O-H⋯O and O-H⋯N hydrogen bonding and additional urotropine solvate mol-ecules into chains, which are further connected into layers. These layers combine into a three-dimensional network by pairs of centrosymmetric inter-molecular C-H⋯S hydrogen bonds. In the crystal structure of compound 2, di-thio-cyanato-(urotropine)tri-ethano-lcobalt(II), the cobalt cation is octa-hedrally coordinated to two terminal N-bonded thio-cyanate anions, one urotropine ligand and three ethanol mol-ecules into discrete complexes, which are located in general positions. These complexes are linked by inter-molecular O-H⋯N hydrogen bonding into layers, which are further connected into a three-dimensional network by inter-molecular C-H⋯S hydrogen bonding.

Dataset Information

An Interprotein Co-S Coordination Complex in the B₁₂-Trafficking Pathway.

Publications

An Interprotein Co-S Coordination Complex in the B<sub>12</sub>-Trafficking Pathway.

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Dataset Information

An Interprotein Co-S Coordination Complex in the B12-Trafficking Pathway.

Publications

An Interprotein Co-S Coordination Complex in the B<sub>12</sub>-Trafficking Pathway.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

An Interprotein Co-S Coordination Complex in the B₁₂-Trafficking Pathway.