A Certain GTP-Binding Protein Can Exist in Two Main States

Short Answer

A certain GTP-binding protein can exist in two main states. When bound to GDP, it is mostly cytosolic. In its GTP-bound form, however, it associates with the cytosolic face of the endoplasmic reticulum (ER) membrane, where it hydrolyzes the bound GTP after a short delay and is released again into the cytosol. You have created and expressed green fluorescent protein (GFP) fusions of the wild-type protein, as well as that of a mutant protein that does not bind GTP as readily as the wild type. You then perform a fluorescence recovery after photobleaching (FRAP) experiment by photobleaching a small area of the ER membrane and measuring GFP fluorescence recovery over time. According to the results below, which curve (1 or 2) do you think corresponds to the wild-type fusion protein? Write down 1 or 2 as your answer.