Cyanobacteria and red algae use light-harvesting pigments bound by proteins to
capture solar radiation and to channel excitation energy into their reaction
centres. In most cyanobacteria, a multi-megadalton soluble structure known as
the phycobilisome is a major light-harvesting system. Allophycocyanin is the
main component of the phycobilisome core, forming a link between the rest of the
phycobilisome and the reaction-centre core. The crystal structure of
allophycocyanin from Thermosynechococcus elongatus (TeAPC) has been determined
and refined at 3.5 A resolution to a crystallographic R value of 26.0% (R(free)
= 28.5%). The structure was solved by molecular replacement using the
allophycocyanin structure from Spirulina platensis as the search model. The
asymmetric unit contains an (alphabeta) monomer which is expanded by symmetry to
a crystallographic trimer.
