Module 2 Lecture 4 PDF

1. P-ATPase Transport involves phosphorylated Asp and conformation shifts Multi-domain protein has all transporter activities 1 ATP hydrolyzed; multiple cations (co)transported per cycle 2. F or V-ATPase Transport uses a rotary mechanism (multi-subunit complexes) 3 ATPs...

1. P-ATPase Transport involves phosphorylated Asp and conformation shifts Multi-domain protein has all transporter activities 1 ATP hydrolyzed; multiple cations (co)transported per cycle 2. F or V-ATPase Transport uses a rotary mechanism (multi-subunit complexes) 3 ATPs hydrolyzed (or synthesized) per rotation 2 to 4 H+ (or Na+) transported per ATP V-ATPase Vacuolar membrane ATP dependent proton pumps V-ATPase transport proton across the membranes. V-ATPase uses ATPs to transport H+ ions. V-ATPases are found within the membranes of many organelles, such as endosomes, lysosomes macrophages, neutrophils. V-ATPase complex structure, consists of two domains. Vo and V1 (Like that of Mitochondrial ATPase (Fo and F1). V1 domain is cytosolic hydrophilic domain and Vo transmembrane domain with multiple subunits in each domain. Binding and hydrolysis of ATP in V1 provide the energy for pumping of H+ ions through Vo domain.  F-type and V-type ATPases are membrane-associated molecular machines that couple the transfer of protons or sodium cations across the membrane with ATP hydrolysis or synthesis. These enzymes represent the cornerstone of cellular bioenergetics and are ubiquitous to all three domains of life (bacteria, archaea and eukaryotes). The F-type F0, F1 ATPases are found in the mitochondria and chloroplasts of all eukaryotic cells and in most bacteria. V-type ATPases occur in eukaryotic cytoplasmic membranes (in particular, vacuoles). 3. ATP-binding cassette (ABC) Transporters Each has 2 ABC and 2 transmembrane domains/subunits Transport by dimerization of ABCs and shifting of TMDs 1-2 ATP hydrolyzed per molecule transported P-class pumps Na+/K+ ATPase pump Na+/K+ ATPase pump, pumps 2 K+ in and 3 Na+ out important for many cellular functions (osmotic balance of cells) 3 Na+ out for every 2 K+ ions in uses ATP as energy source binding of phosphate from ATP drives conformation change that allows ions to be transported to appropriate sides an asparate residue becomes phosphorylated and the energy transfer changes the proteins conformational shape Na+ binding sites switch from high affinity on inside to low affinity on outside to allow for binding of Na+ on inside and release of Na+ ions on outside K+ binding sites switch from high affinity on outside to low affinity on inside for the same reason can be blocked with poisons like ouabain or digitalis blocked pump can't transport ions across membrane and the chemical gradients for Na and K slowly disappear due to continuous action of the leak channels, resting potential removed the potential built up in the Na+ ions will be used by many different processes i.e. cotransporters, neuronal signaling etc.  Sodium Glucose Cotransporter Glucose is one of the most important molecules to act as basic fuel for the brain and other vital organs. Because of its central role in metabolism, most cells have evolved to have an apparatus to sense and transport extracellular glucose into the cells or have adaptive machinery to obtain glucose during fasting. There are 2 classes of glucose carriers described in mammalian cells: active sodium-glucose cotransporters (SGLTs) and facilitative glucose transporters (GLUTs). Sodium-glucose cotransporters (SGLTs) are a group of transporter proteins that cotransport glucose and sodium intracellularly using the sodium-potassium gradient generated by the SGLTs use the movement of Na+ down its electrochemical gradient to drive the uptake of glucose, which is maintained by the Na+ pump. SGLT1 is responsible for glucose absorption from the small intestine, and SGLT2, which accounts for reabsorption of most of the glucose filtered in urine. SGLT inhibitors for improving Healthspan and lifespan  The active transport of Ca2+ across the plasma membrane is driven by a Ca2+ pump that is structurally related to the Na+ -K+ pump and is similarly powered by ATP hydrolysis. It is very important that they maintain low concentrations of Ca2+ for proper cell signalling. Ca2+ is a secondary messenger require for cell signaling. (cyclic AMP, cyclic GMP also Secondary messengers). High levels of cytoplasmic calcium can also cause the cell to undergo apoptosis. Ca2+ require for muscle contraction.  The plasma membrane Ca2+ ATPase (PMCA) is a transport protein in the plasma membrane of cells that functions as a calcium pump to remove calcium (Ca2+) from the cell. PMCA function is vital for regulating the amount of Ca2+ within all eukaryotic cells. There is a very large transmembrane electrochemical gradient of Ca2+ driving the entry of the ion into cells, yet it is very important that they maintain low concentrations of Ca2+ for proper cell signaling. Thus, it is necessary for cells to employ ion pumps to remove the Ca2+. The PMCA and the sodium calcium exchanger (NCX) are together the main regulators of Sodium calcium pump  Sodium calcium pump The sodium-calcium exchanger (Na+- Ca2+ exchanger or NCX) is a membrane protein that removes Ca2+ from the cells. It uses the electrochemical potential energy to allow Na+ to flow across the plasma membrane in exchange for the counter transport of Ca2+. A single calcium ion is exported for the import of three sodium ions, which results in depolarization. The exchanger exists in many different cell types including cardiac, skeletal, smooth muscle, and neuronal cells. It is considered one of the most important cellular mechanisms for removing Ca2+ in a resting state, by  The sodium-calcium exchanger is an antiporter membrane protein that removes calcium from cells. It uses electrochemical gradient of sodium (Na+). It allows three sodium ions into the cell to transport one calcium ion out from the cell. Sodium calcium pump which has low affinity to Ca2+ ions. Functions of Sodium calcium pump: - Cardiac muscle relaxation - Maintenance of low Ca2+ concentration in cytoplasm -