FIGURE 4. The dynamic interplay between O-GlcNAc and O-phosphate enables the rapid generation of enormous molecular diversity in response to cellular stimuli.

The cycling of two post-translational modifications that are independently regulated, such as that of O-GlcNAcylation and phosphorylation, on the same polypeptide, provides the cell with a rapid-response mechanism for generating enormous molecular diversity to fine-tune protein interactions and functions. As the number (n) of potential modification sites increases, the potential molecular diversity increases drastically. This example illustrates the maximal theoretical molecular diversity if the two modifications independently and reciprocally compete for the same sites. Red, molecular diversity = 2ⁿ; blue, molecular diversity = 3ⁿ.