What defines G-protein coupled receptors (GPCRs)?

G-protein coupled receptors (GPCRs) are characterized as α-helical integral membrane proteins, which is a defining feature of their structure and function. These receptors span the cell membrane multiple times, typically around seven times, creating a structure made up of α-helical segments of amino acids. This specific configuration is crucial for their role in transmitting signals from outside the cell to the interior, allowing them to activate intracellular G-proteins upon ligand binding.

The α-helical structure provides the necessary topology for ligand binding and subsequent conformational changes that facilitate G-protein activation. This is essential for the diverse range of physiological responses mediated by GPCRs, such as sensory perception, immune responses, and neurotransmission. Understanding this structural aspect is fundamental to the study of cell signaling pathways and pharmacology, given that many drugs target GPCRs to elicit their effects.

In contrast, while GPCRs do have lipid elements due to their membrane localization, they are not primarily lipid-based, and their functionality depends heavily on their protein structure. Although some GPCRs can form dimers or oligomers, they are not universally homodimeric, making it an inaccurate characterization to define GPCRs overall. GPCRs can interact with ligands