Biliary secretory immunoglobulin A is a major constituent of the new group of cholesterol crystal-binding proteins.
OBJECTIVE
Recently we described a new group of lectin-bound biliary proteins that bind to cholesterol crystals, modify crystal morphology, and inhibit cholesterol crystallization. The aim of the current study was to characterize and identify individual members of this group of cholesterol crystal-binding proteins.


METHODS
Crystal-binding proteins were purified from human gallbladder bile by lectin affinity chromatography and preparative gel electrophoresis. Purified crystal-binding proteins were characterized by using cholesterol crystal-growth assays, immunoblotting, and amino acid analysis. For comparison, identified biliary proteins were isolated from gallbladder bile by lectin affinity and immunoaffinity chromatography.


RESULTS
The individual crystal-binding proteins with molecular weights of 74, 63, and 28 kilodaltons inhibited cholesterol crystallization in a dose-dependent manner (2.5-10 micrograms/mL). Immunoblotting with specific antibodies and N-terminal amino acid sequences revealed that the 74-kilodalton crystal-binding protein is the secretory component, the 63-kilodalton protein is the heavy chain, and the 28-kilodalton protein is the light chain of human secretory immunoglobulin (Ig) A. Isolated biliary IgA showed a potent inhibitory effect on cholesterol crystallization in model bile even at levels less than physiological concentrations (1-100 micrograms/mL).


CONCLUSIONS
Biliary secretory IgA is a major constituent of the previously described group of cholesterol crystal-binding proteins. Crystal-binding IgA may be an important modulator of crystal agglomeration into stones and stone growth in vivo.
Busch
N
N
Department of Internal Medicine III, University of Technology, Aachen, Germany.
Lammert
F
F
Matern
S
S
D000595:Amino Acid Sequence; D001646:Bile / Q000737:chemistry* / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002769:Cholelithiasis / Q000209:etiology; D002784:Cholesterol / Q000378:metabolism*; D002846:Chromatography, Affinity; D003460:Crystallization; D006801:Humans; D007071:Immunoglobulin A, Secretory / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data
D002352:Carrier Proteins; D007071:Immunoglobulin A, Secretory; D002784:Cholesterol