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The structural changes elicited by the C11N mutation and by three combinations of mutations situated along possible evolutionary paths connecting the Aquifex aeolicus and the Escherichia coli enzyme are described. All four mutants are not capable of binding metal and lack the structural asymmetry among subunits with regard to substrate binding and conformation of the L7 loop.

The crystallized structure of the Saccharomyces cerevisiae class I ubiquitin-conjugating enzyme, Ubc7 was solved using molecular replacement techniques. The analysis of the protein revealed that its ubiquitin-accepting cysteine is located between the fourth strand, S4 of the beta-sheet and the second alpha-helix, B. A hypervariable surface region was also identified which is thought to be the position responsible for the enzyme's interaction with different E3 proteins or substrates.

Structural analysis has been performed to determine the geometry of bovine thrombin complexed noncovalently with a substrate analog, G17phi(super 2), in which the Arg-16f/Gly-17f peptide bond is replaced with uncleavable analog of residues 7f-19f of fibrinogen Aalpha. At 2.3 angstroms, data indicate that the geometry is consistent with a model of the Michealis complex. The structure consists of three independent complexes in the asymmetric unit and indicate the interactions of the P2' and P3' residues on the carboxyl-terminal side of the scissile bond.

The article explains the electronic structures of the metal centers present in the [Cd.sup.2+], [Zn.sup.2+] and [Cu.sup.2+] substituted forms of Aquifex aeolicus 3-deoxy-d-manno-octulosonate 8-phosphate synthase (KDO8PS). The rate of product released from the synthase is shown to be completely dependent on the metal used in the enzyme.

The three-dimensional structure of the noncovalent hexamer of dihydroorotase (DHO) and aspartate transcarbamoylase (ATC) from the hyperthermophile Aquifex aeolicus is described. The entrances and the interior of the chamber are both electropositive suggesting that the architecture of the nanoreactor has modified the kinetics of the bisynthase, not only by steric channeling but also by preferential escape of the product, dihydroorotase, which is less negatively charged than its precursors.