T=75 icosahedral carboxysome
The carboxysome enhances CO2 fixation inside many photosynthetic and chemoautotrophic bacterial cells by encapsulating the key enzymes ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) and carbonic anhydrase. Interestingly this structure is icosahedral like viral capsid and has a T=75 symmetry .
T=75 icosahedral carboxysome is composed of 12 pentameric and 740 hexameric capsomeres for a total of 4500 carboxysome proteins.
Icosahedric triangulation number is calculated following Caspar and Klug system
D. L. Caspar, A. Klug
Cold Spring Harb. Symp. Quant. Biol. 1962; 27: 1?24