The function of allergens may determine allergenicity

Grass group I allergens (beta-expansins) are novel, papain-related proteinases

Expansins are a family of proteins that catalyse long-term extension of isolated plant cell walls due to an as yet unknown biochemical mechanism. They are divided into two groups, the alpha-expansins and beta-expansins, the latter group consisting of grass group I allergens and their vegetative homologs. These grass group I allergens, to which more than 95% of patients allergic to grass pollen possess IgE antibodies, are highly immunologically crossreactive glycoproteins exclusively expressed in pollen of all grasses. Alignments of the amino-acid sequences of grass group I allergens derived from diverse grass species reveal up to 95% homology. It is therefore likely that these molecules share a similar biological function. The major grass group I allergen from timothy grass (Phleum pratense), Phl p 1, was chosen as a model glycoprotein and expressed in the methylotrophic yeast Pichia pastoris to obtain a post-translationally modified and functionally active allergen. The recombinant allergen exhibited proteolytic activity when assayed with various test systems and substrates, which was also subsequently demonstrated with the natural protein, nPhl p 1. These observations are confirmed by amino-acid alignments of Phl p 1 with three functionally important sequence motifs surrounding the active-site amino acids of the C1 (papain-like) family of cysteine proteinases. Moreover, the significantly homologous alpha-expansins mostly share the functionally important C1 sequence motifs. This leads us to propose a C1 cysteine proteinase function for grass group I allergens, which may mediate plant cell wall growth and possibly contributes to the allergenicity of the molecule.

From housekeeper to microsurgeon: the diagnostic and therapeutic potential of ribonucleases

The RNA population in cells is controlled post-transcriptionally by ribonucleases (RNases) of varying specificity. Angiogenin, neurotoxins, and plant allergens are among many proteins with RNase activity or significant homology to known RNases. RNase activity in serum and cell extracts is elevated in a variety of cancers and infectious diseases. RNases are regulated by specific activators and inhibitors, including interferons. Many of these regulatory molecules are useful lead compounds for the design of drugs to control tumor angiogenesis, allergic reactions, and viral replication. One RNase (Onconase) and several RNase activators are now in clinical trials for cancer treatment or inhibition of chronic virus infections. Several others, alone or conjugated with specific cell binding molecules, are being developed for their antifungal, antiviral, and antitumor cell activity.