Autori: Cosmin Ionel Sicora, Felix M. Ho, Tiina Salminen, Stenbjörn Styring, Eva-Mari Aro

Editorial: Biochimica et Biophysica Acta (BBA) - Bioenergetics , 1787, p.105-112, 2009.

Rezumat:

Cyanobacteria, contrary to higher plants, have a small psbA gene family encoding the reaction centre D1 protein
subunit of photosystem II, the first macromolecular pigment-protein complex of the photosynthetic electron
transport chain. Modulation of expression of multiple psbA genes in the family allows cyanobacteria to adapt to
changing environmental conditions. To date, two different strategies for regulation of the psbA genes have
emerged. One, characterized in Synechocystis PCC6803 and Gloeobacter violaceus PCC7421 involves the
increased expression of one type of D1 protein to cope with the increased rate of damage. The other strategy, in
Synechococcus PCC7942 and Anabaena PCC7120, is to replace the existing D1 with a new D1 form for the
duration of the stress. However, most of the psbA gene families characterized to date contain also a divergent,
apparently silent psbA gene of unknown function. This gene, present in Synechocystis, Anabaena and
Thermosynechococcus elongatus BP-1 was not induced by any stress condition applied so far. Our data shows a
reversible induction of the divergent psbA gene during the onset of argon-induced microaerobic conditions in
Synechocystis, Anabaena and Thermosynechococcus elongatus. The unitary functional response of three
unrelated cyanobacterial species, namely the induction of the expression of the divergent psbA gene as a
reaction to the same environmental cue, indicates that these genes and the protein they encode are part of a
specific cellular response to microaerobic conditions. There are no specific primary structure similarities
between the different microaerobic inducible D1 forms, designated as D1′. Only three amino acid residues are
consistently conserved in D1′. These modifications are: G80 to A, F158 to L and T286 to L. In silico mutation of
the published D1 structure from Thermosynechococcus did not reveal major modifications. The point by point
effects of the mutations on the local environment of the PSII structure are also discussed.

Cuvinte cheie: psbA, cianobacterii, proteina D1, fotosinteza // psbA, Microaerobic effect, D1 protein, Cyanobacteria