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- Description:
- Fish allergies are common in Europe, particularly among male children and young adults. Children allergic to fish react variably to different species.Cod is among the most common offenders, while salmon is the one besttolerated. The allergy-eliciting protein has been isolated from the whitemuscle albumin. It is a parvalbumin, designated Allergen M. Parvalbumins arecalcium (Ca)-binding proteins of low molecular weight. Like many other Ca-binding proteins, they belong to the EF-hand family characterised byhelix-loop-helix (HLH) binding motifs (two helices pack together at an angleof ~90 degrees, separated by a loop region where calcium binds). In the parvalbumin HLH structural motif, calcium is coordinated through one carbonyl oxygen atom and the oxygen-containing side-chains of 5 amino acidresidues, or 4 residues and a water molecule.Initially, parvalbumins were detected in relatively high amounts in lowervertebrate white muscle, where they were thought to be important for fibrerelaxation. They were subsequently found, although in lesser amounts, in thefast twitch skeletal muscles of higher vertebrates, as well as in a varietyof non-muscle tissues, including testis, endocrine glands, skin and specificneurons. There are two distinct phylogenetic lineages: alpha and beta. Mostmuscles contain parvalbumin of only alpha or beta origin. Cod parvalbumin belongs to the beta-lineage and shares significant similarity with parvalbumin of other fish species.Allergen M contains 113 residues, is a homogenous acidic protein and belongsto a group of muscle sarcoplasmic proteins. It carries the major allergenicdeterminants associated with cod sensitivity, which is dependent directly onthe linear structure rather than on the molecular conformation. The allergenic activity of allergen M resides in particular epitopes found inthree loops: AB (~13-33), CD (~48-64) and EF (~80-103). It has an N-acetylterminal amino acid residue and includes 1 residue of glucose attached to the conserved N-terminal cysteine, and 1 residue each of tyrosine, tryptophan and arginine - the arginine is believed to play a key role in maintaining the tertiary structure. Mutation of the last conservedcoordinating residue of the Ca-binding loop (E101D-motif 4) has also beenshown to have a significant impact on the ability of the mutant to obtainthe sevenfold coordination preferred by Ca2+.
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