For decades, scientists have debated whether there is a common evolutionary origin for the different photosynthetic (1) organisms present today.

Reporting in todays Nature journal, scientists from the Wolfson Laboratories, Department of Biological Sciences, Imperial College, now provide evidence for a link.

They have discovered a new protein supercomplex in the photosynthetic pathway that links two major proteins that were previously thought to work autonomously.

The key proteins Photosystem I (PSI) and Photosystem II (PSII), work together in the photosynthetic pathway to produce oxygen, and energy for plants to grow (2).

The Imperial researchers investigated the possibility of this link using cyanobacteria, a major photosynthetic producer in the worlds oceans. Tom Bibby and colleagues were investigating the role of a PSII-like protein that is produced by cyanobacteria in conditions of low-iron availability (3). They expected this protein to interact with PSII, due to its DNA sequence similarity with one of its proteins.

By recreating 'iron-stress response' conditions in cyanobacteria, the team found that this PSII-like protein interacts, surprisingly, with PSI, by forming a light harvesting antenna of 18 chlorophyll molecules around the protein complex.

The presence of the antenna increases the light harvesting ability by approximately 72 per cent compared with that of the normal PSI alone.

This means that cyanobacteria can produce oxygen even in low iron conditions. This adaptation would have global environmental significance - both for creating the levels of oxygen in the atmosphere that allowed the
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Contact: Taslima Khan
taslima.khan@ic.ac.uk
44-20-7594-6712
Imperial College London
15-Aug-2001