ATP-dependent

No abstract

The topological similarity of IL-10 to IFN gamma was totally unexpected, and may be a reflection of the close relationship between the biological effects of these two cytokines. The structure of IL-10 provides insights into the possible modes of conversion of the dimer into monomers, and of putative sites of receptor interactions. The good level of refinement and high resolution of this structure show that the internal disorder often associated with other helical cytokines is not an essential feature of this class of proteins.

The crystal structure of a 1:1 complex between the German cockroach allergen Bla g 2 and the Fab fragment of a monoclonal antibody 7C11 was solved at 2.8-Å resolution. Bla g 2 binds to the antibody through four loops that include residues 60 -70, 83-86, 98 -100, and 129 -132. Cation-interactions exist between Lys-65, Arg-83, and Lys-132 in Bla g 2 and several tyrosines in 7C11. In the complex with Fab, Bla g 2 forms a dimer, which is stabilized by a quasi-four-helix bundle comprised of an ␣-helix and a helical turn from each allergen monomer, exhibiting a novel dimerization mode for an aspartic protease. A disulfide bridge between C51a and C113, unique to the aspartic protease family, connects the two helical elements within each Bla g 2 monomer, thus facilitating formation of the bundle. Mutation of these cysteines, as well as the residues Asn-52, Gln-110, and Ile-114, involved in hydrophobic interactions within the bundle, resulted in a protein that did not dimerize. The mutant proteins induced less ␤-hexosaminidase release from mast cells than the wild-type Bla g 2, suggesting a functional role of dimerization in allergenicity. Because 7C11 shares a binding epitope with IgE, the information gained by analysis of the crystal structure of its complex provided guidance for site-directed mutagenesis of the allergen epitope. We have now identified key residues involved in IgE antibody binding; this information will be useful for the design of vaccines for immunotherapy.Cockroach allergy is associated with the development of asthma and is a risk factor for emergency room admission of asthmatic patients, especially among inner city children living in low-income houses infested with cockroaches (1, 2). Cockroaches release allergens to the environment, which are carried by particles (5-40 m of diameter) that reach the lung by inhalation. Bla g 2 is one of the most important cockroach allergens, eliciting production of specific IgE in ϳ70% of cockroach-allergic patients at exposure levels that are 10 -100-fold lower than those from other common indoor allergens from dust mite and cat (3-5). Exposure to Bla g 2 results in cross-linking of IgE bound to the surface of mast cells or basophils from sensitized patients (i.e. in immunological terms, cross-linking refers to the non-covalent linkages between the allergen and two IgE molecules at the surface of mast cells or basophils), and induces release of potent mediators (histamine, leukotrienes, prostaglandins, etc.) of allergic reactions.We recently solved the crystal structure of Bla g 2, confirming that the overall fold of this allergen corresponds to that of pepsin-like aspartic proteases, and revealing structural elements that explain why it is enzymatically inactive (6, 7). Bla g 2 contains important amino acid substitutions in the area corresponding to the catalytic site. These modifications impair enzymatic function, and the allergen did not show proteolytic activity in standard in vitro assays using casein and hemoglobin as substrates (7). Bla g 2 belongs to a gro...