New insights into the thermostability of bacterial ferredoxins: high-resolution crystal structure of the seven-iron ferredoxin from Thermus thermophilus.
The crystal structure of the seven-iron ferredoxin from Thermus thermophilus (FdTt) has been determined at 1.64 A resolution, allowing us to unveil the common mechanisms of thermostabilization within "bacterial-type" ferredoxins. FdTt and other homologous thermophilic seven-iron ferredoxins are smaller than their mesophilic counterparts. Thermostabilizing features are optimized in a minimal structural and functional unit, with an extensive cross-linking of secondary structure elements mediated by improved polar and hydrophobic interactions. Most of the potentially stabilizing features are focused on the vicinity of the functional [3Fe-4S] cluster. The structural [4Fe-4S] cluster is shielded in thermophilic FdTt by an increased number of polar interactions involving the two N-terminal residues. Comparisons with the hyperthermostable ferredoxin from Thermotoga maritima reveal that (1) a reduction in the number of non-glycine residues in strained conformations, (2) improved polar interactions within the common iron-sulfur cluster binding (betaalphabeta)2 motif, and (3) an optimized charge distribution at the protein surface, constitute a common strategy for increasing the thermal stability of these ferredoxins.
Macedo-Ribeiro
S
S
Max-Planck-Institut für Biochemie, Abteilung Strukturforschungm, Martinsried, Germany. sandra@aramis.ibmc.up.pt
Martins
B M
BM
Pereira
P J
PJ
Buse
G
G
Huber
R
R
Soulimane
T
T
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D018360:Crystallography, X-Ray; D005288:Ferredoxins / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D016963:Thermus thermophilus / Q000737:chemistry*
D005288:Ferredoxins