Journal Article

Iron deficiency induces the formation of an antenna ring around trimeric photosystem I in cyanobacteria

Nield, Jon, Bibby, Thomas S., Barber, James

2001

Overview

Although iron is the fourth most abundant element in the Earth's crust, its concentration in the aquatic ecosystems—particularly the open oceans—is sufficiently low to limit photosynthetic activity and phytoplankton growth 1 , 2 . Cyanobacteria, a major class of phytoplankton, respond to iron deficiency by expressing the ‘iron-stress-induced’ gene, isiA (ref. 3 ). The protein encoded by this gene has an amino-acid sequence that shows significant homology with one of the chlorophyll a -binding proteins (CP43) of photosystem II (PSII) 4 , 5 . The precise function of the CP43-like protein, here called CP43′, has not been elucidated, although there have been many suggestions 3 , 6 . Here we show that CP43′ associates with photosystem I (PSI) to form a complex that consists of a ring of 18 CP43′ molecules around a PSI trimer. This significantly increases the size of the light-harvesting system of PSI. The utilization of a PSII-like protein as an extra antenna for PSI emphasises the flexibility of cyanobacterial light-harvesting systems, and seems to be a strategy which compensates for the lowering of phycobilisome and PSI levels in response to iron deficiency.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: antenna ring / Aquatic ecosystems / Bacteria / Bacterial Proteins - chemistry / Bacterial Proteins - genetics / Bacterial Proteins - metabolism / Bacterial Proteins - physiology / Bacterial Proteins - ultrastructure / Bacteriology / Biological and medical sciences / Carrier Proteins - chemistry / Carrier Proteins - genetics / Carrier Proteins - metabolism / Carrier Proteins - physiology / Carrier Proteins - ultrastructure / CP43' protein / Crystallography, X-Ray / Cyanobacteria - metabolism / Cyanobacteria - physiology / Cyanobacteria - ultrastructure / Cyanophyta / Ecosystems / Fundamental and applied biological sciences. Psychology / Humanities and Social Sciences / Iron / Iron - physiology / isiA gene / letter / Light-Harvesting Protein Complexes / Marine ecosystems / Metabolism. Enzymes / Microbiology / multidisciplinary / Nutrient deficiency / Oceans / Photosynthetic Reaction Center Complex Proteins - chemistry / Photosynthetic Reaction Center Complex Proteins - metabolism / Photosynthetic Reaction Center Complex Proteins - ultrastructure / Phycobilisomes / Phytoplankton / Phytoplankton - chemistry / Phytoplankton - physiology / Phytoplankton - ultrastructure / Protein Conformation / Science / Science (multidisciplinary)