Iron-Sulfur World in Aerobic and Hyperthermoacidophilic Archaea Sulfolobus

Figure 1

Comparative structures by superposition of archaeal zinc-containing ferredoxins from S. tokodaii (6Fe form, mostly gray, and pink for Asp48 and Cys86; 1xer.pdb [47, 48]) and A. ambivalens (7Fe form, transparent orange; 2vkr.pdb [49]), drawn in B-factor putty mode with PyMOL <http://pymol.sourceforge.net/> (a), and their close-up view by superposition of the cluster II site (c). In panels (a) and (c), key residues are labeled; pink asterisk indicates the special iron of the cluster II, which is missing in the 6Fe form (1xer.pdb). Typical fast-scan film voltammogram (at 400 mV⋅s^-1) of the 6Fe form of zinc-containing ferredoxin purified from S. tokodaii [17, 44] (measured with a pyrolytic graphite “edge” (PGE) electrode in 5 mM each of MES/PIPES/HEPES buffer, pH 7.0, containing 100 mM NaCl and 0.2 mg/ml poly-L-lysine (Sigma) as a protomer [16]; Couple A^′ (for [3Fe-4S]^1+/0), 𝐸_1/2=−296 mV (versus NHE); Couple C^′ (for [3Fe-4S]^0/2-), 𝐸_1/2=−700 mV (versus NHE); note that wave couple B for [4Fe-4S]^2+/1+ (𝐸_1/2=−530 mV versus NHE) [16] was undetectable in the cyclic voltammogram) [T.I. and K. Tanaka, unpublished results] (b).