ABSTRACT Body color variation is widespread among animals, and the melanocortin 1 receptor (MC1R) acts as a vital switch gene in regulating pigmentation. A small number of amino acid substitutions, or even a single one, in MC1R are known to influence the body coloration of animals. To investigate the associations between MC1R variants and body color variation in melanistic and non‐melanistic populations of a toad‐headed lizard, P. versicolor , we obtained the complete coding sequences of the MC1R gene. Sequence analysis identified two amino acid substitutions—V165I and V237I, located in transmembrane domains 4 (TM4) and 6 (TM6), respectively—that were significantly associated with color variation in P. versicolor . In silico structural analysis incorporating these two substitutions demonstrated that the melanistic MC1R exhibited stronger binding affinity for α‐MSH, as characterized by a smaller binding surface area and volume, a greater number of hydrogen bonds, more favorable binding free energy, a higher binding constant, and a lower dissociation constant. These changes may ultimately enhance melanin synthesis in melanistic populations. Our results provide insights into how amino acid substitutions affect receptor–ligand‐binding capacity by altering the pocket size of MC1R in P. versicolor .
Tong et al. (2026) studied this question.