The Sso7d protein of Sulfolobus solfataricus

The physiological role of the nonspecific DNA-binding protein Sso7d from the crenarchaeon Sulfolobus solfataricus is unknown. In vitro studies have shown that Sso7d promotes annealing of complementary DNA strands (Guagliardi et al. 1997), induces negative supercoiling (Lopez-Garcia et al. 1998), and chaperones the disassembly and renaturation of protein aggregates in an ATP hydrolysis-dependent manner (Guagliardi et al. 2000). In this study, we examined the relationships among the binding of Sso7d to double-stranded DNA, its interaction with protein aggregates, and its ATPase activity. Experiments with 1-anilinonaphthalene-8-sulfonic acid as probe demonstrated that exposed hydrophobic surfaces in Sso7d are responsible for interactions with protein aggregates and double-stranded DNA, whereas the site of ATPase activity has a non-hydrophobic character. The interactions of Sso7d with double-stranded DNA and with protein aggregates are mutually exclusive events, suggesting that the disassembly activity and the DNA-related activities of Sso7d may be competitive in vivo. In contrast, the hydrolysis of ATP by Sso7d is independent of the binding of Sso7d to double-stranded DNA or protein aggregates

Hydration studies on the archaeal protein Sso7d using NMR measurements and MD simulations

<p>Abstract</p> <p>Background</p> <p>How proteins approach surrounding molecules is fundamental to our understanding of the specific interactions that occur at the surface of proteins. The enhanced surface accessibility of small molecules such as organic solvents and paramagnetic probes to protein binding sites has been observed; however, the molecular basis of this finding has not been fully established. Recently, it has been suggested that hydration dynamics play a predominant role in controlling the distribution of hot spots on surface of proteins.</p> <p>Results</p> <p>In the present study, the hydration of the archaeal multifunctional protein Sso7d from <it>Solfolobus solfataricus </it>was investigated using a combination of computational and experimental data derived from molecular dynamics simulations and ePHOGSY NMR spectroscopy.</p> <p>Conclusions</p> <p>We obtained a convergent protein hydration landscape that indicated how the shape and stability of the Sso7d hydration shell could modulate the function of the protein. The DNA binding domain overlaps with the protein region involved in chaperon activity and this domain is hydrated only in a very small central region. This localized hydration seems to favor intermolecular approaches from a large variety of ligands. Conversely, high water density was found in surface regions of the protein where the ATP binding site is located, suggesting that surface water molecules play a role in protecting the protein from unspecific interactions.</p

An intracellular protease of the crenarchaeon Sulfolobus solfataricus, which has sequence similarity to eukaryotic peptidases of the CD clan.

We purified from crude extracts of the hyperthermophilic crenarchaeon Sulfolobus solfataricus a protease that is able to hydrolyse proteins with a pH optimum of 7.5 and a temperature optimum of 70 degrees C. Assays in the presence of classical protease inhibitors showed that the hydrolytic activity is sensitive to thiol-blocking reagents. Fluorescence assays using synthetic peptides demonstrated that the protease has a preference for cleaving glutamic acid residues. The first 12 residues of the protease match the N-terminus residues of a hypothetical protein in the S. solfataricus genome of 95 amino acids in length and calculated molecular mass of 11072 Da. The whole sequence of the protease is not related to any known protein, but it bears a segment which is highly similar to one containing the active cysteine residue in eukaryotic peptidases known as legumains. This is the first protease isolated from S. solfataricus capable of degrading native proteins effectively. Our results add to the knowledge of the intracellular proteolytic machine in hyperthermophilic micro-organisms