|
Peanut agglutinin is a 110,000 molecular weight lectin composed of four identical subunits of approximately 27,000 daltons each. PNA binds preferentially to a commonly occurring structure, galactosyl (b-1,3) N-acetylgalactosamine. This carbohydrate sequence (called the “T-antigen”) is present in many glycoconjugates such as M and N blood groups, gangliosides, and many other soluble and membrane-associated glycoproteins and glycolipids. With certain exceptions, the receptor sequence for PNA is normally sialylated which prevents the lectin from binding to its receptor oligosaccharide (see Jacalin). In fact, even sialic acid which is not bound directly to the receptor sugars may inhibit binding. Although PNA appears not to require any divalent cations for activity, the presence of calcium ions in diluents can enhance the binding of PNA to receptors, possibly by neutralizing the negative charges on sialic acid residues adjacent to the receptor sequence.
PNA is useful in distinguishing between normal and tumor tissues and in assessing malignancy in transitional mucosa. In addition, PNA binding has been employed as a measure of cellular maturity in lymphoid tissues, to distinguish a variety of lymphocyte subpopulations in man and experimental animals, and to measure the levels of lymphoid cell populations in many diseases. PNA has been employed in the fractionation of stem cells in mice for use in bone marrow transplantation across histocompatibility barriers. |