Final answer:
The protein association mainly mediated by ionic bond is between SOS and Ras. GRB2 interacts with SOS through ionic bonding, which leads to the activation of the Ras protein and the subsequent signaling pathway.
Step-by-step explanation:
The protein association mainly mediated by ionic bond is between SOS and Ras. Upon binding of epidermal growth factor (EGF) to the EGF receptor (EGFR), two proteins associated with the receptor called GRB2 and SOS. GRB2 interacts with SOS through ionic bonding, which leads to the activation of the Ras protein and the subsequent signaling pathway.