PROSITE documentation PDOC00748

Antenna complexes alpha and beta subunits signatures

In photosynthetic bacteria the antenna complexes function as light-harvesting systems that absorb light radiation and transfer the excitation energy to the reaction centers. The antenna complexes are generally composed of two polypeptides (α and β chains); two or three bacteriochlorophyll (BChl) molecules and some carotenoids [1,2].

Both the α and the β chains of antenna complexes are small proteins of 42 to 68 residues which share a three-domain organization. They are composed of a N-terminal hydrophilic cytoplasmic domain followed by a transmembrane region and a C-terminal hydrophilic periplasmic domain. In the transmembrane region of both chains there is a conserved histidine which is most probably involved in the binding of the magnesium atom of a bacteriochlorophyll group. The β chains contain an additional conserved histidine which is located at the C-terminal extremity of the cytoplasmic domain and which is also thought to be involved in bacteriochlorophyll-binding.

We have developed signature patterns for the α and for the β subunits. These signature patterns include the conserved histidine residues.