ABSTRACT
A recombinant form of the elongation factor 2 from the archaeon Sulfolobus solfataricus (SsEF-2), carrying the A26G substitution, has been produced and characterized. The amino acid replacement converted the guanine nucleotide binding consensus sequences A-X-X-X-X-G-K-[T,S] of the elongation factors EF-G or EF-2 into the corresponding G-X-X-X-X-G-K-[T,S] motif which is present in all the other GTP-binding proteins. The rate of poly(U)-directed poly(Phe) synthesis and the ribosome-dependent GTPase activity of A26GSsEF-2 were decreased compared to SsEF-2, thus indicating that the A26G replacement partially affected the function of SsEF-2 during translocation. In contrast, the A26G substitution enhanced the catalytic efficiency of the intrinsic SsEF-2 GTPase triggered by ethylene glycol [Raimo, G., Masullo, M., Scarano, G., & Bocchini, V. (1997) Biochimie 78, 832-837]. Surprisingly, A26GSsEF-2 was able to hydrolyse GTP even in the absence of ethylene glycol; furthermore, the alcohol increased the affinity for GTP without modifying the catalytic constant of A26GSsEF-2 GTPase. Compared to SsEF-2, the affinity of A26GSsEF-2 for [3H]GDP was significantly reduced. These findings suggest that A26 is a regulator of the biochemical functions of SsEF-2. The involvement of this alanine residue in the guanine nucleotide-binding pocket of EF-2 or EF-G is discussed.
Subject(s)
Consensus Sequence , GTP Phosphohydrolase-Linked Elongation Factors/metabolism , Guanine Nucleotides/metabolism , Peptide Elongation Factors/metabolism , Sulfolobus/metabolism , Base Sequence , Binding Sites , DNA Primers , Enzyme Activation , Mutagenesis, Site-Directed , Peptide Elongation Factor 2 , Peptide Elongation Factors/chemistry , Sulfolobus/enzymologyABSTRACT
The crystal structure of superoxide dismutase (SOD) from the hyper thermophile Sulfolobus solfataricus has been determined at 2.3 A resolution by molecular replacement and refined to a crystallographic R-factor of 16.8 % (Rfree 19.8 %). The crystals belong to the space group C2 (a=76.3 A, b=124.3 A, c=60.3 A, beta=128.8 degrees) with two identical monomers in the asymmetric unit. The monomer has a molecular weight of 24 kDa and consists of 210 amino acid residues of which 205 are visible in the electron density map. The overall fold of the monomer of S. solfataricus SOD is similar to that of the other known Fe or Mn-SODs. S. solfataricus SOD forms a very compact tetramer of a type similar to that of SOD from the hyperthermophile Aquifex pyrophilus. Both structures show an elevated number of inter-subunit ion-pairs compared with the mesophilic SOD from Mycobacterium tuberculosis and the thermophilic SOD from Thermus thermophilus. However, in contrast to the A. pyrophilus SOD structure, the number of intra-subunit ion-pairs as well as inter- subunit hydrogen bonds is not higher than in the compared mesophilic and thermophilic SOD structures. The electron density also revealed an unexpected and unusual covalent modification of a conserved tyrosine in the active site. Its involvement in the specific activity of the enzyme is discussed.
Subject(s)
Sulfolobus/enzymology , Superoxide Dismutase/chemistry , Amino Acid Sequence , Binding Sites , Crystallography, X-Ray , Histidine/metabolism , Models, Molecular , Molecular Sequence Data , Protein Conformation , Sequence Homology, Amino Acid , Tyrosine/chemistry , Tyrosine/metabolismABSTRACT
The present article is a review of the work done on the elongation factors EF-1 alpha, EF-2 and EF-1 beta isolated from the hyperthermophilic archaeon Sulfolobus solfataricus. The molecular, physical and biochemical properties of the intact, truncated, mutant or chimeric forms are described and compared.
Subject(s)
Peptide Elongation Factors/chemistry , Sulfolobus/chemistry , Escherichia coli/chemistry , Kinetics , Mutation , Peptide Elongation Factor 1 , Peptide Elongation Factor 2 , Peptide Elongation Factor Tu/chemistry , Peptide Elongation Factors/genetics , Recombinant Fusion Proteins/metabolism , Structure-Activity Relationship , Sulfolobus/enzymologyABSTRACT
Bovine seminal RNase (BS-RNase) is a dimeric member of the pancreatic-like ribonuclease superfamily, with antitumor activity. We report here that recombinant Met(-1) BS-RNase is a less potent cytotoxic factor, while structurally and catalytically indistinguishable from BS-RNase isolated from natural sources. Mature recombinant BS-RNase instead displays full antitumor action. This suggests that the conformation of the N-terminal region of BS-RNase is among the structural determinants of its antitumor action, in addition to its catalytic activity and its quaternary structure.
