Crystal structure of the major celery allergen Api g 1: molecular analysis of cross-reactivity.

Many patients who have been sensitised to pollen, display allergic symptoms after ingestion of certain plant food such as fresh fruit, vegetables and nuts. The cause is the cross-reactivity between structurally very similar major plant allergens. In particular, allergy to celery is very frequently associated with birch and mugwort pollen sensitization, known as to the birch-mugwort-celery syndrome. The crystal structure of the major celery allergen Api g 1, a homologue of the major birch pollen allergen Bet v 1, has been determined to a resolution of 2.9 A. The structure of Api g 1 is very similar to that of Bet v 1 with major differences occurring in the segment comprised of residues 23-45, preceding the well conserved glycine-rich P-loop, as well as in loops beta3-beta4 and beta5-beta6. In particular, Api g 1 lacks E45, which has been shown to be a crucial residue for antibody recognition in the crystal complex of Bet v 1 with the Fab fragment of a murine monoclonal IgG (BV16) antibody. The absence of E45 and the structural differences in the preceding segment suggest that this region of the Api g 1 surface is probably not responsible for the observed cross-reactivity with Bet v 1. A detailed analysis of the molecular surface in combination with sequence alignment revealed three conserved surface patches which may account for cross-reactivity with Bet v 1. Several residues of Bet v 1 which have been shown by mutagenesis studies to be involved in IgE recognition belong to these conserved surface regions. The structure of Api g 1 and the related epitope analysis provides a molecular basis for a better understanding of allergen cross-reactivity and may lead to the development of hypoallergens which would allow a safer immunotherapy.

Crystal structure of a hypoallergenic isoform of the major birch pollen allergen Bet v 1 and its likely biological function as a plant steroid carrier.

Bet v 1l is a naturally occurring hypoallergenic isoform of the major birch pollen allergen Bet v 1. The Bet v 1 protein belongs to the ubiquitous family of pathogenesis-related plant proteins (PR-10), which are produced in defense-response to various pathogens. Although the allergenic properties of PR-10 proteins have been extensively studied, their biological function in plants is not known. The crystal structure of Bet v 1l in complex with deoxycholate has been determined to a resolution of 1.9A using the method of molecular replacement. The structure reveals a large hydrophobic Y-shaped cavity that spans the protein and is partly occupied by two deoxycholate molecules which are bound in tandem and only partially exposed to solvent. This finding indicates that the hydrophobic cavity may have a role in facilitating the transfer of apolar ligands. The structural similarity of deoxycholate and brassinosteroids (BRs) ubiquitous plant steroid hormones, prompted the mass spectrometry (MS) study in order to examine whether BRs can bind to Bet v 1l. The MS analysis of a mixture of Bet v 1l and BRs revealed a specific non-covalent interaction of Bet v 1l with brassinolide and 24-epicastasterone. Together, our findings are consistent with a general plant-steroid carrier function for Bet v 1 and related PR-10 proteins. The role of BRs transport in PR-10 proteins may be of crucial importance in the plant defense response to pathological situations as well as in growth and development.

Comparison of natural and recombinant forms of the major fish allergen parvalbumin from cod and carp.

Allergic reaction following fish consumption can trigger life-threatening reactions in predisposed individuals. Parvalbumins from different species have been identified as the major fish allergens. There are two distinct phylogenetic lineages of parvalbumins, alpha and beta. Most allergic reactions are caused by beta-parvalbumins. We cloned and expressed cDNAs encoding cod (Gadus morhua) and carp (Cyprinus carpio) beta-parvalbumins and purified natural cod beta-parvalbumin. CD spectra of the purified proteins showed that their overall secondary structure contents were very similar. No differences in thermal stability were monitored in the calcium-bound or calcium-depleted form of natural cod parvalbumin. IgE reactivity was assessed using 26 sera of fish allergic patients from Spain, The Netherlands, and Greece in immunoblot and ELISA experiments. Twenty-five of the 26 patients with IgE reactivity to native and recombinant cod parvalbumin also reacted to the recombinant carp parvalbumin. IgE inhibition assays were performed using cod and carp extracts and purified recombinant parvalbumin of cod and carp. High crossreactivity among cod and carp parvalbumins was observed in immunoblots as well as in fluid phase assays. Natural and recombinant parvalbumins gave comparable results when performing various in vitro diagnostic assays.

Lab scale and medium scale production of recombinant allergens in Escherichia coli.

Recombinant products have become invaluable tools for diagnostic as well as therapeutic purposes in modern medicine. Especially in cases where raw naturally derived products are difficult to standardize, well-defined recombinant single components represent the matter of choice. In the recent past, much effort has been undertaken to define individual proteins derived from various sources like pollen, spores of moulds, pet dander, and food causing Type 1 allergic reactions in humans. Therefore, methods for cloning, sequencing, and expressing cDNAs coding for allergens in Escherichia coli became of great interest to allergologists. For the recombinant production of allergens, suitable expression systems, growing conditions, and purification steps have to be established for each individual product. Finally, the purified recombinant allergen has to be carefully investigated for the biochemical, biophysical, and immunological properties. In the following paper, several prokaryotic expression systems, purification strategies, and analytical methods will be presented and pitfalls discussed.