All cells synthesize and coat themselves with specific varieties of glycan structures which are critical for cell regulation, communication, and identification. A ubiquitous characteristic of cancerous and other diseased cells is atypical cell surface glycosylation, which significantly affects cell behavior and environment. These specialized and aberrant glycan patterns have been correlated with the prognosis of malignant cells. In fact, many tumor-targeting antibodies are directed against specific cancerous glycan epitopes.
Changes in glycosylation patterns are a result of up-regulation or down-regulation of the enzymes that synthesize glycans. These changes are caused by abnormal gene mutations which allow opportunities for diseased cells to evolve a more and more robust glycan coat to promote its strength and proliferation.
More investigation is needed to reveal the precise mechanisms and interactions involved with these specifically evolved glycan structures which allow growth and prosperity within the immune system. With the emergence of glycoscience comes the necessity for advanced tools to progress this field of study. Lectin microarray technology has surpassed the traditional use of mass spectrometry for glycomics analysis in both efficiency and capability. Lectin microarrays provide the ability to profile binding patterns for a variety of glycoforms - from individual polysaccharides to whole cells - while also being quick, easy, and requiring minimal sample volume. Below is an example of the information that can be revealed by testing cancerous human serum on Z Biotech's Lectin Microarray.
We selected 26 lectins to include in our first-generation lectin microarray. These 26 lectins represent most carbohydrate-binding epitopes and have been characterized on our glycan arrays. There are 8 or 16 identical subarrays on a single array chip so that 8 or 16 samples can be analyzed simultaneously. Our lectin microarray provides scientists with a powerful and sensitive tool for analyzing glycosylation profiles of therapeutic proteins, biomarkers, or other proteins of interest.
Typical Binding Assay Result from the Lectin Microarray
Example 1: The Lectin Microarray was assayed with a biotinylated alpha-L-fucose target (0.01 μg/ml), followed by streptavidin-Cy3 (1 μg/ml). The array was scanned with a microarray scanner at 532nm wavelength. The positive control shows binding as expected. Three lectins, AAL, UEA-I, and LTA, show specific binding to the target.
Example 2: The Lectin Microarray was assayed with AlexaFluor555-labeled cancerous (breast cancer) and healthy human serum (1:50 dilution). The array was scanned at 532nm wavelength. Data is normalized by equalizing the sum of the 26 lectin intensities on the cancerous and healthy sample subarrays. There is no binding to positive control because the samples were pre-labeled. By comparing healthy to cancerous sera on this array we can observe differences in glycosylation patterns. One such observation is that the PNA lectin (L15) binding is relatively low in the cancerous sample, indicating that its known binding epitope – T antigen – is hypo-expressed in the cancerous serum. There is also relatively increased HPA lectin (L20) binding in the cancerous sample, indicating that its known binding epitope – Tn antigen – is more prevalent. One explanation for this could be a mutation of the gene encoding Cosmc in the cancer patient. Cosmc is a chaperone required for the expression of the enzyme that synthesizes T antigen from Tn antigen, and a deficiency in this pathway would result in more Tn antigen and less T antigen. In addition, there is increased DSA lectin (L5) binding in the cancerous sample, indicating elevated tri- or tetra-antennary complex-type N-glycans. This suggests an overexpression of GlcNAcT-IV, the enzyme that mediates the biosynthesis of tri- or tetra-antennary N-glycans by adding a 4-linked GlcNAc onto the 3-mannose arm.
Example 3: The Lectin Microarray was assayed with AlexaFluor555-labeled fetuin glycoprotein and asialofetuin glycoprotein (50 µg/ml). The array was scanned at 532nm wavelength. Data is normalized by the signal of the lectin with the highest binding affinity. There is no binding to a positive control (a biotinylated probe) because the samples were labeled with fluorescence. By comparing fetuin and asialofetuin on this array we can observe differences in glycosylation (sialylation) patterns. The clearest observation is that there is a relative increase in binding to strong galactose binders (i.e., RCA-1, ECL, PNA, WFA, SBA) for asialofetuin. As expected, this indicates more exposed galactose epitopes where there lacks a sialic acid terminus.