CRYSTALLIZATION AND PRELIMINARY STRUCTURAL STUDIES OF FTR FROM Synechocytis

Shaodong Dai and Hans Eklund

Department of Molecular Biology, Swedish University of Agricultural Sciences

Ferredoxin:thioredoxin reductase (FTR) is the key enzyme of the ferredoxin/thioredoxin system, the light-dependent enzyme regulatory system in oxygenic photosynthesis. The light signal is transmitted in the form of electrons from the chlorophyll-containing thylakoid membranes via a ferredoxin, ferredoxin:thioredoxin reductase (FTR) and thioredoxins which activate or deactivate target enzymes by reduction of regulatory disulfide bridges. FTR catalyzed the crucial step in this important regulatory pathway, e.g., the two-electron reduction of active site disulfide in thioredoxin by sequential one-electron oxidation of the ferredoxin.

FTR is a unique 4Fe-4S iron sulfur protein. It has both disulfide active site and 4Fe- 4S cluster which have a new biological role involving both the production and stabilization of a thiyl radicalintermediate. Recently we obtained crystals of FTR from Synechocytis sp. PCC6803. The crytals are dark brown colour with maximum dimension of 0.12 mm but diffract beyond 3A on raxisII. These crystals belong to the space group of P41212, a=b=45 .2, c=172. 8 A, with one molecule in an asymmetric unit. Heavy atom, Au, Pt, Hg were soaked and the complete data sets were collected. Structural Determination is in progress.