ADENYLYLSULPHATE REDUCTASE FROM THE SULFATE-REDUCING ARCHAEON ARCHAEOGLOBUS-FULGIDUS - CLONING AND CHARACTERIZATION OF THE GENES AND COMPARISON OF THE ENZYME WITH OTHER IRON-SULFUR FLAVOPROTEINS
N. Speich et al., ADENYLYLSULPHATE REDUCTASE FROM THE SULFATE-REDUCING ARCHAEON ARCHAEOGLOBUS-FULGIDUS - CLONING AND CHARACTERIZATION OF THE GENES AND COMPARISON OF THE ENZYME WITH OTHER IRON-SULFUR FLAVOPROTEINS, Microbiology, 140, 1994, pp. 1273-1284
Adenylylsulphate (adenosine-5'-phosphosulphate, APS) reductase from th
e extremely thermophilic sulphate-reducing archaeon Archaeoglobus fulg
idus is an iron-sulphur flavoprotein containing one non-covalently bou
nd flavin group, eight non-haem iron and six labile sulphide atoms per
molecule. Reevaluation of the enzyme structure revealed the presence
of two different subunits with molecular masses of 80 and 18.5 kDa. Th
e subunits are arranged in an alpha(2) beta subunit structure. We have
cloned and sequenced a 2.7 kb segment of DNA containing the genes for
the alpha and beta subunits, which we designate aprA and aprB, respec
tively. The two genes are separated by 17 bp and localized in the orde
r aprBA. While a putative promoter could not be identified in the vici
nity of aprBA a probable termination signal was found just downstream
of the translation stop codon of aprA. The codon usage for aprBA shows
strong preferences for G and C in the third codon position. aprA enco
des a 73.3 kDa polypeptide, which shows significant overall similariti
es with the flavoprotein subunits of the succinate dehydrogenases from
Escherichia coli and Bacillus subtilis and the corresponding flavopro
tein of E. coli fumarate reductase. Part of the homologous peptide str
etches could be assigned to domains that are involved in the binding o
f the substrate or of the FAD prosthetic group. aprB encodes a 17.1 kD
a polypeptide representing an iron-sulphur protein, seven cysteine res
idues of which are arranged in two clusters typical of ligands of the
iron-sulphur centres in ([Fe3S4][Fe4S4]) 7-Fe ferredoxins.