Glycans have several distinct properties that make their development as disease biomarkers appealing.
Firstly, their location on cell surfaces makes them the first point of contact for cellular interactions, and thus
they are crucial in the control of normal metabolic processes, and conversely, they function as pathogen
adhesion receptors. Secondly, specific glycan structures that are not present, or are in low amounts in normal
state, proliferate or alter their sequence in disease states. And, lastly, changes in glycosylation may be found
in many proteins, including those that are highly abundant. Thus changes in the normal levels of glycan
structures, such as terminal sialic acid, may be markers of disease states. New highly-specific reagents are
required in order to overcome current limitations in the discovery and exploitation of disease-related glycans.
Using structurally-guided genetic manipulations, we are converting the NanB sialidase from S. pneumococcus
into a high-specificity affinity reagent for the detection of all types of sialic acid modifications of glycopeptides
and glycoproteins. Because such a protein has lectin-like properties, but is derived from an enzyme, it is called
a "Lectenz®". A NanB Lectenz® addresses a key need in disease glycomarker detection: namely, a robust and
easy to produce reagent specific for detecting all types of sialylated glycans. This reagent could be employed
in an affinity matrix for sample enrichment, which in conjunction with existing MS based methods could provide
linkage information. Glycopeptide sample enrichment aids glycomic analyses by eliminating non-glycosylated
peptides, which would otherwise attenuate the signals from glycopeptides that have low ionization efficiency.
Glycosylation site mapping is essential in fully characterizing and exploiting glycans as markers of specific
disease states, but at present, no reagent exists that can detect sialylated glycans, independent of the type of
linkage associated with the sialic acid. Thus, at present, a number of reagents with varying specificities and
affinities must be employed to capture or detect all forms of sialylated glycans.
Lectenz® offer numerous advantages over plant lectins: they are engineered to be high affinity and yet retain
the exquisite substrate specificity of the endogenous enzyme, they may be efficiently produced, and for human
homologues have the potential to be employed in vivo with low toxicity. Whereas some aspects of Lectenz®
development parallel those of antibody evolution, Lectenz® have the tremendous benefit of employing a protein
naïve template that has the desired specificity.