Dear Tushar,

Leptin binds with fucose, mannose and galactose. The platelet membrane.seems to express endogenous lectin-like activity.  

 Dear Prof. Kandaswami,

Thank you for this information. I guess the molecules or sugar  residues you mentioned are part of some glycoprotein. Is it correct? If it is so, which is that protein? Is it possible to detect it with Western blot (using lectin as a probe, analogous to a primary antibody)? At what molecular weight can we expect a band corresponding to lectin specific glycoprotein?

Dear Tamara,

Thank you for the kind clarification! I regret that it is a typing error on my part!! I am conversant with the adipokine, "leptin".  I could not have meant "leptin"!  Tushar's question is on lectin.  What I wrote as "leptin" should read "lectin". Tushar's question is "What does lectin bind to on a blood vessel?"  I stand corrected on the spelling, "lectin" as opposed to " leptin".

The fact that my second sentence reads as " The platelet membrane seems to express endogenous lectin-like activity" shows that I meant lectin instead of leptin. Obviously, it may be confusing, between "lectin" and "leptin". 

Leptin has been regarded to play critical roles in controlling energy balance in vertebrates; evidence has been reported for the existence of an authentic avian leptin protein gene (LEP) predominantly expressed in the brain and pituitary tissues. The biochemical mechanisms fostering caloric homeostasis and appetite control in humans are enormously complex involving two crucial signal molecules, insulin and leptin (a protein with 146 amino acids). Accrued evidence suggests that leptin and its receptor play a role in human obesity. However, the findings in humans are not as clear-cut as in the mouse.

The role of the hormones, leptin and adiponectin, adipokines predominantly synthesized in the adipose tissue, has been actively investigated in mammary tumor growth; both these critical proteins/hormones, expressed in breast cancer, are potentially linked to the process of carcinogenesis, in particular in the obesity-related breast cancer. Adipose tissue, which consists of mature adipocytes, macrophages and undifferentiated fibroblasts, plays a critical role in the development of breast cancer.  An unstable adipose tissue microenvironment might tremendously influence carcinogenesis of the breast and could have an immense impact on breast cancer development.   The procarcinogenic effect of leptin and anticarcinogenic activity of adiponectin are well known.  

Tushar,

Lectins are specific carbohydrate-binding (binding specific carbohydrate structures on cell surfaces) proteins, ubiquitously distributed in animals, plants and microorganisms. Certain lectins, such as calnexin, function as chaperones in protein folding.  Lectins from animals foster   cell-cell contact.  A lectin generally possesses two or more binding sites for carbohydrate units; some lectins form oligomers with multiple binding sites. The lectin binding sites on the surface of one cell interact with a mosaic of carbohydrates projected surface of another cell. Different classes of lectins are recognized based on their amino acid sequences and biochemical properties. One large class is the C type (for calcium-requiring) occurring in animals. Proteins designated as “selectins” are members of the C-type family; they bind immune system cells to the sites of injury in the course of the inflammatory response. Changes in the amino acid residues of a lectin that interact with the carbohydrate modify the carbohydrate-binding specificity of the lectin. In a C-type carbohydrate-binding domain from an animal lectin, a calcium ion ion links a mannose residue to the lectin. 

Dear Tushar,

Lectins from tomato bind to oligomers of glucosamine.

Lectin activity was described some 150 years ago, when cell agglutination by snake venom and hemagglutination (the clumping of erythrocytes) by castor beans were described. Lectins are proteins of nonimmune origin containing one or more catalytic domains, which reversibly bind to mono- or oligosaccharides. Some lectins binding monomeric mannose are also known. Certain mammalian serum glycoprotein glycans possess terminal sialic acid residues; upon cleavage, these residues expose galactose residues, which bind to asialoglycoprotein receptors, which are C-type galactose specific lectins. Selectins, C-type lectins (see answers above) facilitate the adhesion of leukocytes to endothelial cells of blood vessels. This adhesion is caused by selectin-carbohydrate interaction. Lectins with low affinity to bind to a monosaccharide can bind with much higher affinity to an oligosaccharide containing two or more monosaccharide residues in a favorable linkage. Lectins can bind simultaneously to more than one oligosaccharide.  The biological origin and structure of lectins influence the nature of sugars to which they bind.

Selectins, constitute is one of the families of cell adhesion molecules present in the endothelial glycocalyx, a network of membrane-bound proteoglycans and glycoproteins, covering the endothelium luminally. Glycoproteins from the selectin family possess a terminal lectin domain, which is mainly responsible for the binding of carbohydrate groups on glycosylated proteins or lipids. The glycocalyx of the aortic endothelium recognizes the Wisteria floribunda lectin, which binds N-acetyl-D-galactosamine, while the lectin from Lycopersicon esculentum (tomato) exhibits an affinity for N-acetyl-β-D-glucosamine oligomers.   

Western blot analysis of isolated endothelial cell membrane glycoproteins.  Schumacher U, Vischer P, Völker W, Engelmann B. Lectin binding and uptake and glycoprotein characterization of isolated porcine aortic endothelial and smooth muscle cells. Cell Biochem Funct. 1993 Sep;11(3):225-30. PubMed PMID: 8403237. 

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Has anyone tried to use lectin (LEA) or the antibody directed against the protein that lectin binds to for western blotting ?