True lipases attach triacylglycerols and act at an oil-water interface; they constitute a ubiquitous group of enzymes catalysing a wide variety of reactions, many with industrial potential. But so far the three-dimensional structure has not been reported for any lipase. Here we report the X-ray structure of the Mucor miehei triglyceride lipase and describe the atomic model obtained at 3.1 A resolution and refined to 1.9 A resolution. It reveals a Ser..His..Asp trypsin-like catalytic triad with an active serine buried under a short helical fragment of a long surface loop.

Artemisinins are the most important class of antimalarial drugs. They specifically inhibit PfATP6, a SERCA-type ATPase of Plasmodium falciparum. Here we show that a single amino acid in transmembrane segment 3 of SERCAs can determine susceptibility to artemisinin. An L263E replacement of a malarial by a mammalian residue abolishes inhibition by artemisinins. Introducing residues found in other Plasmodium spp. also modulates artemisinin sensitivity, suggesting that artemisinins interact with the thapsigargin-binding cleft of susceptible SERCAs.

X-ray diffraction analysis (at 2.1-A resolution) of an acid alpha-amylase from Aspergillus niger allowed a detailed description of the stereochemistry of the calcium-binding sites. The primary site (which is essential in maintaining proper folding around the active site) contains a tightly bound Ca2+ with an unusually high number of eight ligands (O delta 1 and O delta 2 of Asp175, O delta of Asn121, main-chain carbonyl oxygens of Glu162 and Glu210, and three water molecules). A secondary binding site was identified at the bottom of the substrate binding cleft; it involves the residues presumed to play a catalytic role (Asp206 and Glu230). This explains the inhibitory effect of calcium observed at higher concentrations. Neutral Aspergillus oryzae (TAKA) alpha-amylase was also refined in a new crystal at 2.1-A resolution. The structure of this homologous (over 80%) enzyme and additional kinetic studies support all the structural conclusions regarding both calcium-binding sites.

Monoclinic crystals of a neutral a-amylase fromAspergillus oryzae, containing three molecules in the asymmetric unit, have been reported previously and studied at 3 A, resolution [Matsuura, Kunusoki, Harada & Kakudo (1984). J. Biochem. 95,[697][698][699][700][701][702].Here we report the solution of the structure of this enzyme in a different crystal form (space group P21212~, a = 50.9, b = 67.2, c = 132.7 A,), with only one molecule in the asymmetric unit. The structure was solved by the molecular replacement method, using a model of acid a-amylase from a related fungus A. niger [Brady, Brzozowski, Derewenda, Dodson & Dodson (1991). Acta Cryst. B47, 527-535]. Conventional least-squares crystallographic refinement failed to converge in a satisfactory manner, and the technique of molecular dynamics in the form of the XPLOR package [Brunger (1988). XPLOR Manual. Yale Univ., USA] was used to overcome the problem. A large rigid-body type movement of the C-terminal domain was identified and accounted for. The final round of restrained least-squares refinement (at 2.1 A. resolution) includ-* Present address to which correspondence should be sent:

In silico screening of combinatorial libraries prior to synthesis promises to be a valuable aid to lead discovery. PRO_SELECT, a tool for the virtual screening of libraries for fit to a protein active site, has been used to find novel leads against the serine protease factor Xa. A small seed template was built upon using three iterations of library design, virtual screening, synthesis, and biological testing. Highly potent molecules with selectivity for factor Xa over other serine proteases were rapidly obtained.