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Since the 1880’s, it has been known that extracts from
certain plants could agglutinate red blood cells. In the 1940’s,
agglutinins were discovered which could “select” types of cells
based on their blood group activities. Although “lectin” was
originally coined to define agglutinins that could discriminate
among types of red blood cells, today the term is used
more generally and includes sugar-binding proteins from
many sources regardless of their ability to agglutinate cells.
Lectins have been found in plants, viruses, microorganisms,
and animals but despite their ubiquity, in many cases their
biological function is unclear.
Most lectins are multimeric, consisting of non-covalently
associated subunits. It is this multimeric structure that gives
lectins their ability to agglutinate cells or form precipitates
with glycoconjugates in a manner similar to antigen-antibody
interactions. This unique group of proteins has provided
researchers with powerful tools to explore a myriad of
biological structures and processes. Because of the specificity
that each lectin has toward a particular carbohydrate structure,
even oligosaccharides with identical sugar compositions can be
distinguished or separated. The affinity between a lectin and
its receptor may vary a great deal due to small changes in the
carbohydrate structure of the receptor. These properties enable
the researcher to discriminate between structures, isolate a
specific glycoconjugate, cell, or virus from a mixture, or study
one process among several. Another property of some lectins
is an ability to induce mitosis in cells that are normally not
dividing. This property has been exploited extensively in an
attempt to understand the process of lymphocyte blastogenesis
and the biochemical and structural alterations associated with
mitogenesis.
Lectins have been purified by “conventional” procedures
including salt-induced crystallization, ethanol precipitation,
ion exchange chromatography and gel filtration, or by
affinity chromatography. The former methods rely on the
physicochemical properties of the proteins for separation while
affinity chromatography depends on the specific interaction
between the lectin and a carbohydrate structure attached to
an inert matrix. We employ both “conventional” procedures
and affinity chromatography for each of our lectins.
Purification is monitored and final product is assessed by
immunoprecipitation with antisera, agglutination titre,
polyacrylamide gel electrophoresis, and binding activity to
specific affinity columns, providing the assurance that our
customers have the best lectins available.
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Agarose Bound Lectins
Lectin affinity chromatography is a simple and widely used
technique for the isolation of a variety of glycoconjugates. The
glycoconjugate is allowed to bind to the immobilized lectin,
and the unbound residual material is removed by washing.
The bound glycoconjugates are generally eluted with a solution
of a sugar known to inhibit binding of the particular lectin.
Soluble glycoproteins, hormones, antigens, polysaccharides,
detergent-solubilized membrane-bound glycoconjugates, cell
surface receptors, blood group substances, viral glycoproteins,
histocompatibility antigens, lymphokines, enzymes, lymphocyte
markers, serum proteins, and oncofetal antigens are only a few
of the substances that have been purified using immobilized
lectins.
Our immobilized lectins are prepared using our affinity-purified
lectins. Heat stable, cross-linked 4% agarose beads with
a molecular weight exclusion limit of about 2x107 daltons
are used as the solid-phase matrix to which the lectins are
covalently coupled. The attachment of the lectins to the beads
is carefully controlled to preserve lectin activity and minimize
conformational changes of the bound lectins that might result
in nonspecific ionic or hydrophobic interactions. The technique
we have developed to couple lectins to agarose beads inserts a
hydrophilic spacer arm between the lectin and the matrix.
This coupling method provides several advantages over the
traditional cyanogen bromide procedure:
Maximum carbohydrate binding activity of the coupled
lectins is retained
Linkage is stable over a range of pH values
Conjugated proteins are not leached off the beads by Tris or
other routinely used buffers
No residual charges are present after conjugation. This
minimizes non-specific binding to the matrix.
Our agarose bound lectins are supplied at a constant
concentration of lectin per ml of settled beads. The
concentration for each lectin is selected to achieve the highest
glycoconjugate binding capacity per mg of lectin present in
the beads. Each lot is tested for its binding capacity using
glycoproteins known to bind the lectin. This provides a
guideline for the user and assures the quality of our agarose
bound lectins.
Labeled Lectins
Some lectins can tolerate a higher degree of conjugation and
still remain fully active, soluble, and retain low nonspecific
binding properties, while others cannot. Each of our labeled
lectins has an appropriate number of fluorochromes or biotins
bound that provides the optimum staining characteristics for
that lectin. These conjugates are supplied essentially free of
unconjugated fluorochromes or biotins, preserved with sodium
azide.
Table of Lectin Properties
A useful table of lectin properties can be be downloaded here.
Additional Information
Thousands of articles on lectins have been published
examining hundreds of different aspects and uses of lectins.
In this catalog, only a few of the uses and properties of each
lectin are described. However, both general and specific
information can be found in the excellent books and articles
listed in the links below.
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General Lectin References
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Lectin Perfusion References (Tomato Lectin)
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