Activating mutants in rat sarcoma (RAS) and B-rapid accelerated fibrosarcoma (BRAF) are found in at least a third of cases of human tumors and melanoma; hence, numerous therapeutic treatments target this pathway. In this letter, we study the adhesion force of RAS-coated beads with BRAF-coated beads, BRAF (A246P) mutant–coated beads, and GST-coated beads using optical tweezers. One full and two fractional RAS–BRAF specific binding modes are identified using the rupture force distribution. The koff (0) of the full binding mode in RAS–BRAF is 3.71×10-4/s and 1.16×10-4s-1 in RAS–BRAF (A246P), whereas the xb is around 3 \times 10-10 m in both groups.