Mutations in the gene encoding the amyloid protein precursor (APP) cause autosomal dominant Alzheimer's disease. Cleavage of APP by unidentified proteases, referred to as beta- and gamma-secretases, generates the amyloid beta-peptide, the main component of the amyloid plaques found in Alzheimer's disease patients. The disease-causing mutations flank the protease cleavage sites in APP and facilitate its cleavage. Here we identify a new membrane-bound aspartyl protease (Asp2) with beta-secretase activity. The Asp2 gene is expressed widely in brain and other tissues. Decreasing the expression of Asp2 in cells reduces amyloid beta-peptide production and blocks the accumulation of the carboxy-terminal APP fragment that is created by beta-secretase cleavage. Solubilized Asp2 protein cleaves a synthetic APP peptide substrate at the beta-secretase site, and the rate of cleavage is increased tenfold by a mutation associated with early-onset Alzheimer's disease in Sweden. Thus, Asp2 is a new protein target for drugs that are designed to block the production of amyloid beta-peptide peptide and the consequent formation of amyloid plaque in Alzheimer's disease.

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A human myelomonocytic cell line, U937, produced an interleukin-1 (IL-1) receptor antagonist protein (IRAP) which was purified and partially sequenced. A complementary DNA coding for IRAP was cloned and sequenced. The mature translation product of the cDNA has been expressed in Escherichia coli and was an active competitive inhibitor of the binding of IL-1 to the T-cell/fibroblast form of the IL-1 receptor. Recombinant IRAP specifically inhibited IL-1 bioactivity on T cells and endothelial cells in vitro and was a potent inhibitor of IL-1 induced corticosterone production in vivo.

The crystal structure of a complex between chemically synthesized human immunodeficiency virus type 1 (HIV-1) protease and an octapeptide inhibitor has been refined to an R factor of 0.138 at 2.5-A resolution. The substrate-based inhibitor, H-Val-Ser-Gln-Asn-Leu psi [CH(OH)CH2]Val-Ile-Val-OH (U-85548e) contains a hydroxyethylene isostere replacement at the scissile bond that is believed to mimic the tetrahedral transition state of the proteolytic reaction. This potent inhibitor has Ki less than 1 nM and was developed as an active-site titrant of the HIV-1 protease. The inhibitor binds in an extended conformation and is involved in beta-sheet interactions with the active-site floor and flaps of the enzyme, which form the substrate/inhibitor cavity. The inhibitor diastereomer has the S configuration at the chiral carbon atom of the hydroxyethylene insert, and the hydroxyl group is within H-bonding distance of the two active-site carboxyl groups in the enzyme dimer. The two subunits of the enzyme are related by a pseudodyad, which superposes them at a 178 degrees rotation. The main difference between the subunits is in the beta turns of the flaps, which have different conformations in the two monomers. The inhibitor has a clear preferred orientation in the active site and the alternative conformation, if any, is a minor one (occupancy of less than 30%). A new model of the enzymatic mechanism is proposed in which the proteolytic reaction is viewed as a one-step process during which the nucleophile (water molecule) and electrophile (an acidic proton) attack the scissile bond in a concerted manner.

Bovine liver rhodanese is a single polypeptide of 293 amino acids in which the halves of the molecule assume analogous tertiary structures in the absence of substantial sequence homology. The sulphur atom transferred during catalysis is bound in persulphide linkage to Cys-247. Substrate binding seems to involve Arg-186 and Lys-249.