The three-dimensional structure of recombinant horseradish peroxidase in complex with BHA (benzhydroxamic acid) is the first structure of a peroxidase-substrate complex demonstrating the existence of an aromatic binding pocket. The crystal structure of the peroxidase-substrate complex has been determined to 2.0 A resolution with a crystallographic R-factor of 0.176 (R-free = 0. 192). A well-defined electron density for BHA is observed in the peroxidase active site, with a hydrophobic pocket surrounding the aromatic ring of the substrate. The hydrophobic pocket is provided by residues H42, F68, G69, A140, P141, and F179 and heme C18, C18-methyl, and C20, with the shortest distance (3.7 A) found between heme C18-methyl and BHA C63. Very little structural rearrangement is seen in the heme crevice in response to substrate binding. F68 moves to form a lid on the hydrophobic pocket, and the distal water molecule moves 0.6 A toward the heme iron. The bound BHA molecule forms an extensive hydrogen bonding network with H42, R38, P139, and the distal water molecule 2.6 A above the heme iron. This remarkably good match in hydrogen bond requirements between the catalytic residues of HRPC and BHA makes the extended interaction between BHA and the distal heme crevice of HRPC possible. Indeed, the ability of BHA to bind to peroxidases, which lack a peripheral hydrophobic pocket, suggests that BHA is a general counterpart for the conserved hydrogen bond donors and acceptors of the distal catalytic site. The closest aromatic residue to BHA is F179, which we predict provides an important hydrophobic interaction with more typical peroxidase substrates.

Ves v 5 is one of three major allergens found in yellow-jacket venom: phospholipase A(1) (Ves v 1), hyaluronidase (Ves v 2), and antigen 5 (Ves v 5). Ves v 5 is related by high amino acid sequence identity to pathogenesis-related proteins including proteins from mammals, reptiles, insects, fungi, and plants. The crystal structure of Ves v 5 has been solved and refined to a resolution of 1.9 A. The majority of residues conserved between the pathogenesis-related proteins can be rationalized in terms of hydrogen bonding patterns and hydrophobic interactions defining an alpha-beta-alpha sandwich core structure. A small number of consensus residues are solvent exposed (including two adjacent histidines) and located in an elongated cavity that forms a putative active site. The site has no structural resemblance to previously characterized enzymes. Homologous antigen 5's from a large number of different yellow jackets, hornets, and paper wasps are known and patients show varying extents of cross-reactivity to the related antigen 5's. The structure of Ves v 5 allows a detailed analysis of the epitopes that may participate in antigenic cross-reactivity, findings that are useful for the development of a vaccine for treatment of insect allergy.

Allergy to house dust mite is among the most prevalent allergic diseases worldwide. Most house dust mite allergic patients react to Der p 1 from Dermatophagoides pteronyssinus, which is a cysteine protease. To avoid heterogeneity in the sample used for crystallization, a modified recombinant molecule was produced. The sequence of the proDer p 1 allergen was modified to reduce glycosylation and to abolish enzymatic activity. The resulting rproDer p 1 preparation was homogenous and stable and yielded crystals diffracting to a resolution of 1.61 Å. The active site is located in a large cleft on the surface of the molecule. The 80-aa pro-peptide adopts a unique fold that interacts with the active site cleft and a substantial adjacent area on the mature region, excluding access to the cleft and the active site. Studies performed using crossed-line immunoelectrophoresis and IgE inhibition experiments indicated that several epitopes are covered by the pro-peptide and that the epitopes on the recombinant mature molecule are indistinguishable from those on the natural one. The structure confirms previous results suggesting a preference for aliphatic residues in the important P2 position in substrates. Sequence variations in related species are concentrated on the surface, which explains the existence of cross-reacting and species-specific antibodies. This study describes the first crystal structure of one of the clinically most important house dust mite allergens, the cysteine protease Der p 1.