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Crystal structures of two functionally different thioredoxins in spinach chloroplasts
G Capitani1, Z Marković-Housley, G DelVal
1Structural Biology Division Biozentrum, University of Basel, Basel, CH-4056, Switzerland. capitani@biocfebs.unizh.ch
Journal of Molecular Biology
|August 31, 2000
Summary
Chloroplast thioredoxins f and m, crucial for photosynthesis, were structurally studied. Despite similar folds, they exhibit distinct surface topologies and active site features, explaining their specific enzyme regulation roles.
Area of Science:
- Biochemistry
- Structural Biology
- Plant Physiology
Background:
- Thioredoxins are essential redox proteins regulating cellular processes.
- Chloroplasts utilize two distinct thioredoxins, f (Trx f) and m (Trx m), with different origins and functions.
- Trx f activates Calvin cycle enzymes, while Trx m targets other chloroplast enzymes.
Purpose of the Study:
- To elucidate the structure-function relationships of chloroplast thioredoxins f and m.
- To understand the molecular basis for their distinct substrate specificities.
Main Methods:
- X-ray crystallography was employed to determine the structures of Trx f and Trx m.
- Structures were solved for oxidized and reduced forms, and for different Trx f variants.
- High-resolution structures (2.1-2.3 Å) were obtained.
Main Results:
- Thioredoxin f typically forms a monomer, while truncated Trx f and Trx m form dimers.
- Both proteins share the conserved thioredoxin fold but differ in surface topology and active site charge distribution.
- Trx f possesses an additional N-terminal alpha-helix and a unique exposed cysteine residue.
Conclusions:
- The structural differences, particularly in surface topology and active site flexibility, underlie the specificities of Trx f and Trx m.
- These findings provide insights into the regulatory mechanisms of photosynthesis.