Final answer:
Ca2+-mediated signal transduction cascades are typically enacted through the protein calmodulin. The process starts with a G protein opening a Ca2+ channel, increasing Ca2+ in the cytoplasm, which then binds to calmodulin. This interaction initiates a series of phosphorylation cascades involving proteins such as protein kinases.
Step-by-step explanation:
Most Ca2+-mediated signal transduction cascades act through the protein calmodulin, a Ca2+-binding protein that is present in every eukaryotic cell. This process begins when a G protein interacts with and opens a Ca2+ channel, leading to an increase in cytoplasmic Ca2+. Calmodulin, after binding to the increased Ca2+, undergoes a conformational change which allows it to activate other proteins and thus initiates various cascades within the target cell. These cascades often involve phosphorylation events, facilitated by enzymes such as protein kinases like PKA (Protein Kinase A) or PKC (Protein Kinase C). Protein phosphorylation changes the shapes and function of proteins, enabling them to activate or inactivate specified pathways leading to a cellular response.
The role of G-proteins is central to this signal transduction. They couple extracellular signals to cellular responses through the exchange of GDP for GTP, which activates them to engage downstream effectors such as adenylyl cyclase, leading to the production of second messengers like cAMP, or phospholipase C, which generates IP3 and DAG, further impacting intracellular signaling pathways.