Answer
When only one type of protein subunit is used in the complex, it is called a homo oligomer or homomer. A homo- tetramer (with 4 identical subunits) can have two symmetries: either a four-fold axis in the cyclic point group C4, or three orthogonal two-fold axes in the dihedral point group D2 (also noted as 222). Both point groups have m = 4, yet they yield very different quaternary structures. Dihedral (Dn) symmetry, which requires the number of subunits to be even
(m = 2n), is very common in globular soluble proteins. Homo-hexamers (with 6 identical subunits) generally have D3 symmetry. An example is Escherichia coli aspartate transcarbamoylase, in which each of the six protomers comprises one catalytic and one regulatory chain.
Work Step by Step
When only one type of protein subunit is used in the complex, it is called a homo oligomer or homomer. A homo- tetramer (with 4 identical subunits) can have two symmetries: either a four-fold axis in the cyclic point group C4, or three orthogonal two-fold axes in the dihedral point group D2 (also noted as 222). Both point groups have m = 4, yet they yield very different quaternary structures. Dihedral (Dn) symmetry, which requires the number of subunits to be even
(m = 2n), is very common in globular soluble proteins. Homo-hexamers (with 6 identical subunits) generally have D3 symmetry. An example is Escherichia coli aspartate transcarbamoylase, in which each of the six protomers comprises one catalytic and one regulatory chain.
