Summary: B12 binding domain
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This is the Wikipedia entry entitled "Vitamin B12-binding domain". More...
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Vitamin B12-binding domain Edit Wikipedia article
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nmr structure of glutamate mutase (b12-binding subunit) complexed with the vitamin b12 nucleotide
|B12-binding_2 (4-helical bundle cap domain)|
how a protein binds b12: a 3.o angstrom x-ray structure of the b12-binding domains of methionine synthase
In molecular biology, the vitamin B12-binding domain is a protein domain which binds to cobalamin (vitamin B12). It can bind two different forms of the cobalamin cofactor, with cobalt bonded either to a methyl group (methylcobalamin) or to 5'-deoxyadenosine (adenosylcobalamin). Cobalamin-binding domains are mainly found in two families of enzymes present in animals and prokaryotes, which perform distinct kinds of reactions at the cobalt-carbon bond. Enzymes that require methylcobalamin carry out methyl transfer reactions. Enzymes that require adenosylcobalamin catalyse reactions in which the first step is the cleavage of adenosylcobalamin to form cob(II)alamin and the 5'-deoxyadenosyl radical, and thus act as radical generators. In both types of enzymes the B12-binding domain uses a histidine to bind the cobalt atom of cobalamin cofactors. This histidine is embedded in a DXHXXG sequence, the most conserved primary sequence motif of the domain. Proteins containing the cobalamin-binding domain include:
- Animal and prokaryotic methionine synthase (EC 18.104.22.168), which catalyse the transfer of a methyl group from methyl-cobalamin to homocysteine, yielding enzyme-bound cob(I)alamin and methionine.
- Animal and prokaryotic methylmalonyl-CoA mutase (EC 22.214.171.124), which are involved in the degradation of several amino acids, odd-chain fatty acids and cholesterol via propionyl-CoA to the tricarboxylic acid cycle.
The core structure of the cobalamin-binding domain is characterised by a five-stranded alpha/beta (Rossmann) fold, which consists of 5 parallel beta-sheets surrounded by 4-5 alpha helices in three layers (alpha/beta/alpha). Upon binding cobalamin, important elements of the binding site appear to become structured, including an alpha-helix that forms on one side of the cleft accommodating the nucleotide 'tail' of the cofactor. In cobalamin, the cobalt atom can be either free (dmb-off) or bound to dimethylbenzimidazole (dmb-on) according to the pH. When bound to the cobalamin-binding domain, the dimethylbenzimidazole ligand is replaced by the active histidine (His-on) of the DXHXXG motif. The replacement of dimethylbenzimidazole by histidine allows switching between the catalytic and activation cycles. In methionine synthase the cobalamin cofactor is sandwiched between the cobalamin-binding domain and an approximately 90 residues N-terminal domain forming a helical bundle comprising two pairs of antiparallel helices. This N-terminal domain forms a 4-helical bundle cap, in the conversion to the active conformation of this enzyme, the 4-helical cap rotates to allow the cobalamin cofactor to bind the activation domain.
- Krautler B (August 2005). "Vitamin B12: chemistry and biochemistry". Biochem. Soc. Trans. 33 (Pt 4): 806–10. doi:10.1042/BST0330806. PMID 16042603.
- Ludwig ML, Matthews RG (1997). "Structure-based perspectives on B12-dependent enzymes". Annu. Rev. Biochem. 66: 269–313. doi:10.1146/annurev.biochem.66.1.269. PMID 9242908.
- Banerjee R, Ragsdale SW (2003). "The many faces of vitamin B12: catalysis by cobalamin-dependent enzymes". Annu. Rev. Biochem. 72: 209–47. doi:10.1146/annurev.biochem.72.121801.161828. PMID 14527323.
- Reitzer R, Gruber K, Jogl G, Wagner UG, Bothe H, Buckel W, Kratky C (August 1999). "Glutamate mutase from Clostridium cochlearium: the structure of a coenzyme B12-dependent enzyme provides new mechanistic insights". Structure 7 (8): 891–902. doi:10.1016/s0969-2126(99)80116-6. PMID 10467146.
- Drennan CL, Huang S, Drummond JT, Matthews RG, Lidwig ML (December 1994). "How a protein binds B12: A 3.0 A X-ray structure of B12-binding domains of methionine synthase". Science 266 (5191): 1669–74. doi:10.1126/science.7992050. PMID 7992050.
- Mancia F, Keep NH, Nakagawa A, Leadlay PF, McSweeney S, Rasmussen B, BÃ¶secke P, Diat O, Evans PR (March 1996). "How coenzyme B12 radicals are generated: the crystal structure of methylmalonyl-coenzyme A mutase at 2 A resolution". Structure 4 (3): 339–50. doi:10.1016/s0969-2126(96)00037-8. PMID 8805541.
- Bandarian V, Pattridge KA, Lennon BW, Huddler DP, Matthews RG, Ludwig ML (January 2002). "Domain alternation switches B(12)-dependent methionine synthase to the activation conformation". Nat. Struct. Biol. 9 (1): 53–6. doi:10.1038/nsb738. PMID 11731805.
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B12 binding domain Provide feedback
This domain binds to B12 (adenosylcobamide)[1-3], it is found in several enzymes, such as glutamate mutase Q05488 methionine synthase Q99707 and methylmalonyl-CoA mutase P22033. It contains a conserved DxHxxGx(41)SxVx(26)GG motif, which is important for B12 binding .
Tollinger M, Konrat R, Hilbert BH, Marsh EN, Krautler B; , Structure 1998;6:1021-1033.: How a protein prepares for B12 binding: structure and dynamics of the B12-binding subunit of glutamate mutase from Clostridium tetanomorphum. PUBMED:9739092 EPMC:9739092
Perez-Marin MC, Padmanabhan S, Polanco MC, Murillo FJ, Elias-Arnanz M;, Mol Microbiol. 2008;67:804-819.: Vitamin B12 partners the CarH repressor to downregulate a photoinducible promoter in Myxococcus xanthus. PUBMED:18315685 EPMC:18315685
External database links
This tab holds annotation information from the InterPro database.
InterPro entry IPR006158
The cobalamin (vitamin B12) binding domain can bind two different forms of the cobalamin cofactor, with cobalt bonded either to a methyl group (methylcobalamin) or to 5'-deoxyadenosine (adenosylcobalamin). Cobalamin-binding domains are mainly found in two families of enzymes present in animals and prokaryotes, which perform distinct kinds of reactions at the cobalt-carbon bond. Enzymes that require methylcobalamin carry out methyl transfer reactions. Enzymes that require adenosylcobalamin catalyse reactions in which the first step is the cleavage of adenosylcobalamin to form cob(II)alamin and the 5'-deoxyadenosyl radical, and thus act as radical generators. In both types of enzymes the B12-binding domain uses a histidine to bind the cobalt atom of cobalamin cofactors. This histidine is embedded in a DXHXXG sequence, the most conserved primary sequence motif of the domain [PUBMED:16042603, PUBMED:9242908, PUBMED:14527323]. Proteins containing the cobalamin-binding domain include:
- Animal and prokaryotic methionine synthase (EC), which catalyse the transfer of a methyl group from methyl-cobalamin to homocysteine, yielding enzyme-bound cob(I)alamin and methionine.
- Animal and prokaryotic methylmalonyl-CoA mutase (EC), which are involved in the degradation of several amino acids, odd-chain fatty acids and cholesterol via propionyl-CoA to the tricarboxylic acid cycle.
- Prokaryotic lysine 5,6-aminomutase (EC).
- Prokaryotic glutamate mutase (EC) [PUBMED:10467146].
- Prokaryotic methyleneglutarate mutase (EC).
- Prokaryotic isobutyryl-CoA mutase (EC).
The core structure of the cobalamin-binding domain is characterised by a five-stranded alpha/beta (Rossmann) fold, which consists of 5 parallel beta-sheets surrounded by 4-5 alpha helices in three layers (alpha/beta/alpha) [PUBMED:7992050]. Upon binding cobalamin, important elements of the binding site appear to become structured, including an alpha-helix that forms on one side of the cleft accommodating the nucleotide 'tail' of the cofactor. In cobalamin, the cobalt atom can be either free (dmb-off) or bound to dimethylbenzimidazole (dmb-on) according to the pH. When bound to the cobalamin-binding domain, the dimethylbenzimidazole ligand is replaced by the active histidine (His-on) of the DXHXXG motif. The replacement of dimethylbenzimidazole by histidine allows switching between the catalytic and activation cycles [PUBMED:8805541]. In methionine synthase the cobalamin cofactor is sandwiched between the cobalamin-binding domain and an approximately 90 residues N-terminal domain forming a helical bundle comprising two pairs of antiparallel helices [PUBMED:8805541].
In methionine synthase, there is a second, adjacent domain involved in cobalamin binding that forms a 4-helical bundle cap (INTERPRO); in the conversion to the active conformation of this enzyme, the 4-helical cap rotates to allow the cobalamin cofactor to bind the activation domain (INTERPRO) [PUBMED:11731805].
The mapping between Pfam and Gene Ontology is provided by InterPro. If you use this data please cite InterPro.
|Molecular function||metal ion binding (GO:0046872)|
|cobalamin binding (GO:0031419)|
Below is a listing of the unique domain organisations or architectures in which this domain is found. More...
The graphic that is shown by default represents the longest sequence with a given architecture. Each row contains the following information:
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a textual description of the architecture, e.g. Gla, EGF x 2, Trypsin.
This example describes an architecture with one
Gladomain, followed by two consecutive
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1Cannot generate PP/Heatmap alignments for seeds; no PP data available
Key: available, not generated, — not available.
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|Seed source:||Pfam-B_359 (release 5.2)|
|Author:||Bateman A, Mian N|
|Number in seed:||133|
|Number in full:||8147|
|Average length of the domain:||115.00 aa|
|Average identity of full alignment:||22 %|
|Average coverage of the sequence by the domain:||16.83 %|
|HMM build commands:||
build method: hmmbuild -o /dev/null HMM SEED
search method: hmmsearch -Z 23193494 -E 1000 --cpu 4 HMM pfamseq
|Family (HMM) version:||14|
|Download:||download the raw HMM for this family|
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Unmapped species names
The tree is built by looking at each sequence in the full alignment for the family. We take the name of the species given by UniProt and try to map that to the full taxonomic tree from NCBI. In some cases, the name chosen by UniProt does not map to any node in the NCBI tree, perhaps because the chosen name is listed as a synonym or a misspelling in the NCBI taxonomy.
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Since we reduce the species tree to only the eight main taxonomic levels, sequences that are mapped to the sub-species level in the tree would not normally be shown. Rather than leave out these species, we map them instead to their parent species. So, for example, for sequences belonging to one of the Vibrio cholerae sub-species in the NCBI taxonomy, we show them instead as belonging to the species Vibrio cholerae.
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The tree shows the occurrence of this domain across different species. More...
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For all of the domain matches in a full alignment, we count the number that are found on all sequences in the alignment. This total is shown in the purple box.
We also count the number of unique sequences on which each domain is found, which is shown in green. Note that a domain may appear multiple times on the same sequence, leading to the difference between these two numbers.
Finally, we group sequences from the same organism according to the NCBI code that is assigned by UniProt, allowing us to count the number of distinct sequences on which the domain is found. This value is shown in the pink boxes.
We use the NCBI species tree to group organisms according to their taxonomy and this forms the structure of the displayed tree. Note that in some cases the trees are too large (have too many nodes) to allow us to build an interactive tree, but in most cases you can still view the tree in a plain text, non-interactive representation. Those species which are represented in the seed alignment for this domain are highlighted.
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There are 5 interactions for this family. More...
We determine these interactions using iPfam, which considers the interactions between residues in three-dimensional protein structures and maps those interactions back to Pfam families. You can find more information about the iPfam algorithm in the journal article that accompanies the website.
For those sequences which have a structure in the Protein DataBank, we use the mapping between UniProt, PDB and Pfam coordinate systems from the PDBe group, to allow us to map Pfam domains onto UniProt sequences and three-dimensional protein structures. The table below shows the structures on which the B12-binding domain has been found. There are 71 instances of this domain found in the PDB. Note that there may be multiple copies of the domain in a single PDB structure, since many structures contain multiple copies of the same protein seqence.
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