Protein transporters are specialized proteins that facilitate the movement of other proteins and molecules across cell membranes. They play a crucial role in maintaining cellular function by ensuring that essential substances, such as nutrients and signaling molecules, enter and exit cells efficiently. These transporters can be classified into two main types: facilitated diffusion transporters, which allow substances to move down their concentration gradient, and active transporters, which require energy to move substances against their gradient. Together, they help regulate various physiological processes, including metabolism and cell communication.