Mapping mutations onto a protein's linear sequence to see where damage clusters and what kind of function is being disturbed.
A protein is a long chain of amino acids. The lollipop mutation plot unfolds this chain into a line: the horizontal axis is amino acid position, colored blocks mark functional domains, and vertical stems show where mutations recur in a cohort.
TP53 is the most frequently mutated gene in human cancer. Its canonical protein product, p53, is 393 amino acids long. Most cancer hotspots fall in the DNA-binding domain, but they do not all break p53 in the same way. R248 and R273 are DNA-contact residues. R175H is usually described as a structural or conformational hotspot because it disrupts the fold near the zinc-binding surface that supports DNA binding.
Figure 1. TP53 mutation hotspots. Lollipop height encodes recurrence in a simulated cohort. The six classic hotspot residues, R175, G245, R248, R249, R273, and R282, cluster in the DNA-binding domain. Color separates DNA-contact hotspots from structural hotspots.
CDKN1A encodes p21, a 164-amino-acid cell-cycle inhibitor that p53 can activate after DNA damage. It is useful as a contrast case. In many tumors, the pathway is disrupted upstream by TP53 mutation, so p21 does not show the same dense hotspot pattern.
Figure 2. CDKN1A lollipop plot. The simulated burden is lower and scattered across the short p21 protein, with the PCNA-interacting PIP box near the C terminus marked separately.