Limunectin. A phosphocholine-binding protein from Limulus amebocytes with adhesion-promoting properties.
A protein that binds to and precipitates with pneumococcal C-polysaccharide and a phosphocholine (PC) derivative of bovine serum albumin has been affinity purified from Limulus amebocytes. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis reveals that the isolated protein consists of a single polypeptide chain of approximately 50 kDa. It is an intracellular protein localized in the secretory granules of amebocytes according to immunogold staining. Although it shares the PC-binding property with C-reactive protein isolated from Limulus and other animal species, it differs from C-reactive protein in that the latter binds to PC only in the presence of Ca2+, whereas the newly isolated protein binds to PC in a Ca(2+)-independent manner. In this respect, the newly isolated PC-binding protein resembles the antibodies to PC of mouse myelomas. The gene coding for this protein has been isolated. The gene sequence predicts a protein of 54 kDa with an unusual structural feature: it consists almost entirely of 10 contiguous segments, 45 amino acids in length, with extensive homology. Some limited sequence homologies were found between the 54-kDa protein and segments of vitronectin, gelatinase, and collagenase. It binds to bacterial cells, fixed amebocytes, and a number of extracellular matrix molecules. Due to its structural and some functional similarities to other adhesion molecules, the Limulus 54-kDa protein was named "Limunectin."
Liu
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Division of Biochemistry and Biophysics, Food and Drug Administration, Bethesda, Maryland 20892.
Lin
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Cislo
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Minetti
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Baba
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Liu
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D000595:Amino Acid Sequence; D000818:Animals; D060829:Arthropod Proteins; D001483:Base Sequence; D001667:Binding, Competitive; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D015815:Cell Adhesion Molecules / Q000302:isolation & purification* / Q000378:metabolism*; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D006737:Horseshoe Crabs / Q000032:analysis* / Q000648:ultrastructure; D005779:Immunodiffusion; D007150:Immunohistochemistry; D013058:Mass Spectrometry; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010767:Phosphorylcholine / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid
D060829:Arthropod Proteins; D002352:Carrier Proteins; D015815:Cell Adhesion Molecules; D010767:Phosphorylcholine; C070119:limunectin protein, Limulus