Dodecameric protein

A dodecameric protein has a quaternary structure consisting of 12 protein subunits in a complex. Dodecameric complexes can have a number of subunit 'topologies', but typically only a few of the theoretically possible subunit arrangements are observed in protein structures.

A dodecamer (protein) is a protein complex with 12 protein subunits.

A common subunit arrangement involves a tetrahedral distribution of subunit trimers (or 3-4-point symmetry). Another observed arrangement of subunits puts two rings of six subunits side by side along the sixfold axis (or 2-6-point symmetry).

Dodecameric proteins include

• Complete gap junction channel, composed of two hexamers.
• glutamine synthetase (PDB code: 2gls)
• Dodecameric ferritin (PDB code: 1qgh)
• Aβ42 - Amyloid-beta 42
• Helicobacter pylori urease
• HHV capsid portal protein

Propionyl-CoA carboxylase

When multiple copies of a polypeptide encoded by a gene form an aggregate, this protein structure is referred to as a multimer. When a multimer is formed from polypeptides produced by two different mutant alleles of a particular gene, the mixed multimer may exhibit greater functional activity than the unmixed multimers formed by each of the mutants alone. In such a case, the phenomenon is referred to as intragenic complementation or interallelic complementation.^[1]

Propionyl-CoA carboxylase (PCC) is a dodecameric heteropolymer composed of α and β subunits in a α6β6 structure. Mutations in PCC, either in the α subunit (PCCα) or β subunit (PCCβ) can cause propionic acidemia in humans. When different mutant skin fibroblast cell lines defective in PCCβ were fused in pairwise combinations, the β heteromultimeric protein formed as a result often exhibited a higher level of activity than would be expected based on the activities of the parental enzymes.^[2] This finding of intragenic complementation indicated that the multimeric dodecameric structure of PCC allows cooperative interactions between the constituent PCCβ monomers that can generate a more functional form of the holoenzyme.

References

1. Crick FH, Orgel LE. The theory of inter-allelic complementation. J Mol Biol. 1964 Jan;8:161-5. doi: 10.1016/s0022-2836(64)80156-x. PMID 14149958
2. Rodríguez-Pombo P, Pérez-Cerdá C, Pérez B, Desviat LR, Sánchez-Pulido L, Ugarte M. Towards a model to explain the intragenic complementation in the heteromultimeric protein propionyl-CoA carboxylase. Biochim Biophys Acta. 2005;1740(3):489-498. doi:10.1016/j.bbadis.2004.10.009

• The Protein Data Bank (PDB)
• Protein Interfaces, Surfaces and Assemblies Server (PISA) part of the PDBe.