Journal:JBIC:10

Crystal structures of the all cysteinyl coordinated D14C variant of Pyrococcus furiosus ferredoxin: [4Fe-4S] <-> [3Fe-4S] cluster conversion

Monika Nøhr Løvgreen, Maja Martic, Michael S. Windahl, Hans E. M. Christensen and Pernille Harris^[1]

Molecular Tour
Structures of the all cysteinyl coordinated D14C variant of ferredoxin from the hyperthermophilic archaeon Pyrococcus furiosus have been determined for the [4Fe-4S] <-> and [3Fe-4S] forms (click to enlarge). The [4Fe-4S] form diffracted to 1.7 Å and two different types of molecules were found in the crystal (2z8q). They have different crystal packing and intramolecular disulfide bond conformation. The crystal packing reveals a beta-sheet interaction between A molecules (shown in blue and green) in adjacent asymmetric units, while B molecules are packed as monomers in a less rigid position next to the A-A extended beta-sheet dimers (shown in red and yellow). The intramolecular disulfide bond in the A molecules is in a double conformation while the intramolecular disulfide bond in the B molecules is in a single conformation (click to see morph, molecule A is shown in blue and molecule B in green).

pH dependent equilibrium of D14C [3Fe-4S] P. furiosus ferredoxin between protonated and deprotonated monomers and formation of a disulfide bonded dimer from deprotonated monomers. Fd is short for ferredoxin.

Two forms of D14C [3Fe-4S] Pyrococcus furiosus ferredoxin are obtained when purified at pH 8.0: a monomer and a dimer connected by an intermolecular disulfide bond (see static image at the left). When purified at pH 5.8, only the monomer is obtained. The [3Fe-4S] form diffracted to 2.8 Å resolution and showed only the monomeric form, which resembles molecule A of D14C [4Fe-4S] Pyrococcus furiosus ferredoxin. Crystal packing in D14C [3Fe-4S] ferredoxin is as extended beta-sheet dimers of adjacent molecules (shown in red and orange), which is the same as WT [3Fe-4S] P. furiosus ferredoxin (1sj1, shown in blue and cyan) even though the space groups are different (see also corresponding side views for D14C [3Fe-4S]) and WT [3Fe-4S]).

PDB reference: Crystal structure of D14C [3Fe-4S] Pyrococcus furiosus ferredoxin, 3pni.