We have isolated and sequenced a 598-bp full length
cDNA clone for the human Charcot-Leyden crystal (CLC)
protein (
eosinophil lysophospholipase), the unique and prominent constituent of human eosinophils and basophils that forms the hexagonal bipyramidal crystals classically observed in tissues and secretions from sites of eosinophil-associated
inflammation. A 426-bp open reading frame encoded a 142-amino
acid polypeptide with a predicted molecular mass of 16.5 kDa and isoelectric point of 7.28. The deduced amino acid sequence of CLC
protein showed 20 to 30% similarity over regions of approximately 100
amino acids with the carboxyl-terminal domains of four
IgE-
binding proteins, including the 31-kDa human and rat
IgE-
binding proteins, the 35-kDa mouse
carbohydrate binding protein (
CBP35), Mac-2, the murine macrophage
cell surface protein that is identical to
CBP35, and the human homologue of Mac-2. These
proteins are members of a superfamily of
beta-galactoside binding S-type
animal lectins, which includes a group of highly conserved 14-kDa
lectins isolated from human lung, heart, placenta, bovine heart, chicken skin, mouse fibroblasts, and the electric organ of the electric eel; CLC
protein also showed sequence similarities to these 14-kDa
animal lectins, including conservation of 7 of 16 invariant
amino acid residues thought to comprise the
carbohydrate-binding domain of these
proteins, with conservative
amino acid changes at others; thus, CLC
protein could potentially possess
carbohydrate or
IgE-binding activities. Northern analyses revealed an approximately 900-bp
mRNA species that was present in peripheral blood eosinophils from patients with
eosinophilia, basophils from patients with
chronic myelogenous leukemia, and in HL-60 cells induced towards eosinophilic differentiation with
B cell growth factor-II (IL-5) or granulocytic differentiation with
DMSO, but was absent in neutrophils, monocytes, T cells, B cells, or HL-60 cells induced towards monocytic differentiation with
vitamin D3. Southern analyses revealed a gene of approximately 5 to 6 kb in length. The
cDNA clone and complete amino acid sequence data for CLC
protein will facilitate structure-function analyses of its unusual hydrophobic properties, unique propensity for crystallization,
lysophospholipase, and potential
lectin-like activities.