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LBL, a novel, developmentally regulated, laminin-binding lectin
Z Z Bao1, J Muschler, A F Horwitz
1Department of Cell and Structural Biology, University of Illinois, Urbana 61801.
Insights
Researchers discovered a novel extracellular matrix molecule, termed laminin-binding lectin (LBL), which functions as a galactoside-binding lectin. This protein binds to laminin and is expressed late in avian development.
Area of Science:
- Extracellular Matrix Biology
- Developmental Biology
- Molecular Biology
Background:
- Integrin preparations often contain associated protein complexes.
- Novel extracellular matrix molecules play crucial roles in tissue structure and development.
- Understanding protein interactions within the extracellular matrix is key to deciphering cellular processes.
Purpose of the Study:
- To purify and characterize a novel 190/220-kDa complex found in integrin preparations.
- To determine the molecular identity, function, and localization of this novel protein.
- To investigate its binding properties and developmental expression pattern.
Main Methods:
- Immunoaffinity purification using monoclonal antibodies.
- Subunit composition analysis and N-terminal amino acid sequencing.
- Hemagglutination assays for lectin activity and carbohydrate-binding specificity.
- Binding assays with extracellular matrix proteins like laminin, fibronectin, and collagen IV.
Main Results:
- A novel extracellular matrix molecule, a trimer of 70-kDa subunits, was purified.
- The protein exhibits galactoside-binding lectin activity and binds specifically to laminin.
- It is widely distributed in basement membranes and connective tissues, with late developmental expression in avian embryos.
- The protein, named laminin-binding lectin (LBL), is conserved and often copurifies with laminin.
Conclusions:
- Laminin-binding lectin (LBL) is a novel extracellular matrix molecule with unique lectin and laminin-binding properties.
- Its late expression suggests a specific role in later stages of avian development.
- LBL's conservation and association with laminin highlight its significance in extracellular matrix composition and function.
Abstract:
A 190/220-kDa complex found in integrin preparations was purified, and monoclonal antibodies were raised against it. The immunoaffinity-purified complex appears to be a trimer of very similar or identical 70-kDa subunits. It is a novel extracellular matrix molecule as determined by its subunit composition, N-terminal amino acid sequence, and in vivo localization. It is distributed widely in basement membranes including those from muscle, nerve, and kidney. It is also present in connective tissue regions such as perineurium and perimysium. It has the unusual property that it is initially expressed very late in avian development near the time of hatching. This protein is found to copurified with integrin because it binds to the carbohydrate support in Sepharose. Hemagglutination assays with mono- and disaccharides show that it functions as a lectin with galactoside-binding specificity. This protein is also found to bind strongly and specifically to laminin at a site distinct from its lectin activity, but does not bind to fibronectin or type IV collagen. The protein appears to be conserved and is a common contaminant of many laminin preparations. We call this novel protein "LBL" for laminin-binding lectin.