Immobilized Boronates Lectins

W. H. Scouten, Utah State University,

Logan, UT, USA

Copyright © 2000 Academic Press

Lectins and boronates have affinity for very similar biological compounds. They are both useful for separating glycoproteins, glycolipids, and other glycated compounds as well as for the separation of sugars and, in the case of boronates, other compounds containing appropriate 1,2 or 1,3 diols. There is, however, a fundamental difference between lectins and boronates. Lectins bind to glycated molecules because of a natural biological interaction between the lectin and the sugar moiety of the glycated compound. Lectins have biological purposes and functions related to this sugar-lectin interaction. On the other hand, boronates have no biological function but serve as a compound which, by chemi-selection, binds to 1,2 or 1,3 vicinal, co-planer, diols. Since many sugars contain such diols, boronates are very useful functioning as a 'chemical lection'. However, lectins have a much higher degree of binding specificity, as would be expected from the fact that biological interactions depend on multiple binding sites and intricate interactions with complex stereochemistry. Thus, any given lectin may bind to a specific sugar; or in other cases, may bind to an array of sugars. Thus, there exists a broad repertoire of lectins that are capable of binding to various types of glycated biomolecules. Fortunately, a sufficient number of lectins are available commercially to provide essentially the entire array of binding sites and, certainly, that array which is needed for biological separations of glycated biomolecules.

The corollary to this is that while boronates have a fairly low degree of specificity, they have a much higher stability than lectins. Thus an immobilized boronate, such as a boronate chromatography matrix, can be stored for years, whereas a lectin may have limited storage and operational stability.

Finally, in lectin affinity chromatography it should be understood that lectins are purified by affinity chromatography on a variety of immobilized sugars. Such 'reverse' lectin chromatography is beyond the scope of this discussion but does provide a methodology for identifying and isolating lectins that have a unique specificity for a particular rare combination of one or more sugar molecules.

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