COPI functions by forming a vesicle coat that facilitates the budding of vesicles from donor membranes. The process begins with the recruitment of ARF1 (ADP-ribosylation factor 1), a small GTPase that, when activated, binds to the membrane and recruits the COPI coat complex. The coat complex is composed of seven subunits, collectively known as the coatomer. This coatomer complex helps in deforming the membrane to form a vesicle and in selecting the cargo that will be transported.
