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* Antenna complexes alpha and beta subunits signatures *
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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 (alpha and beta chains); two  or three bacteriochlorophyll (BChl)
molecules and some carotenoids [1,2].

Both the  alpha and the beta 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 beta  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 alpha and for the beta subunits.
These signature patterns include the conserved histidine residues.

-Consensus pattern: [LIVFA]-x-[GASV]-[LIVFA]-x-[IV]-H-x(3)-[LIVM]-[STE]-
                    [STNH]-x(1,3)-[STN]-W-[LIVMFYW]
                    [The H binds BChl]
-Sequences known to belong to this class detected by the pattern: ALL    alpha
 chains.
-Other sequence(s) detected in SWISS-PROT: NONE.

-Consensus pattern: [EQ]-x(4)-H-x(5)-[AGS]-x(3)-[FY]-x(3)-[AG]-x(2)-[AV]-H-
                    x(7)-P     
                    [The two H bind BChl]
-Sequences known to belong to this class detected by the pattern: ALL     beta
 chains, except for Ectothiorhodospira halochloris B800/830/1020 beta-2.
-Other sequence(s) detected in SWISS-PROT: NONE.

-Last update: June 1994 / First entry.

[ 1] Wagner-Huber R., Brunisholz R.A., Bissig I., Frank G., Suter F., Zuber H.
     Eur. J. Biochem. 205:917-925(1992).
[ 2] Brunisholz R.A., Zuber H.
     J. Photochem. Photobiol. B 15:113-140(1992).