Identification and molecular characterization of Charybdis feriatus tropomyosin, the major crab allergen.
BACKGROUND
Crab sensitivity is one of the most common seafood allergies. However, to date, there has been no report on the molecular characterization of crab allergens and no comparative analysis with other seafood allergens.


OBJECTIVE
This study was undertaken to clone, identify, and determine the primary structure of a major IgE-reactive molecule in crab.


METHODS
We constructed an expression cDNA library from a common crab, Charybdis feriatus. This library was then screened with the use of sera from subjects with a well-documented history of type I hypersensitivity reactions upon ingestion of crab. An IgE-reactive clone was chosen and subcloned into plasmids for nucleotide sequence determination and expression in Escherichia coli.


RESULTS
We identified a 1-kb cDNA designated as Cha f 1. Expression of Cha f 1 produces a 34-kd recombinant protein reactive to the IgE antibodies from patients with crab allergies but not from control subjects. Cha f 1 has an opening reading frame of 264 amino acids and demonstrates marked homology to the shrimp tropomyosin Met e 1. Absorption of allergic sera with Cha f I removes IgE reactivity to crab extract. Moreover, absorption of allergic sera with recombinant shrimp Met e 1 tropomyosin removes IgE reactivity to Cha f 1.


CONCLUSIONS
This 34-kd protein, designated as Cha f 1, is the first identified major allergen of crab. Nucleotide and amino acid comparison shows that this protein is the crab tropomyosin. The molecular basis of shrimp and crab allergy is readily demonstrated at the nucleotide and amino acid level.
Leung
P S
PS
Division of Rheumatology/Allergy and Clinical Immunology School of Medicine, University of California, Davis, CA 95616, USA.
Chen
Y C
YC
Gershwin
M E
ME
Wong
S H
SH
Kwan
H S
HS
Chu
K H
KH
D000485:Allergens / Q000737:chemistry; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D000918:Antibody Specificity; D001483:Base Sequence; D003386:Brachyura / Q000276:immunology*; D002999:Clone Cells / Q000276:immunology; D003429:Cross Reactions / Q000276:immunology; D018076:DNA, Complementary; D005512:Food Hypersensitivity / Q000276:immunology; D006801:Humans; D007073:Immunoglobulin E / Q000276:immunology; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000276:immunology; D014335:Tropomyosin / Q000276:immunology* / Q000302:isolation & purification*
D000485:Allergens; D000596:Amino Acids; D018076:DNA, Complementary; D011994:Recombinant Proteins; D014335:Tropomyosin; D007073:Immunoglobulin E