ATP Powered Pumps

By Adam Attebery

Introduction

• General information about ATP activated pumps

• Four different classes of ATP activated transmembrane proteins

–Function and examples of each

–Mechanism of each

ATP Powered Pumps

• Transport various small particles against concentration gradient

• All ATP powered pumps are transmembrane with ATP binding site on the cytosolic face of membrane.

4 classes of pumps

• P-class pump– Sodium potassium pumps and calcium pumps

• V-class proton pumps– Plasma membrane of osteoclasts

• F-class proton pumps– Inner mitochondrial membrane

• ABC superfamily– Flippase

P-class Pumps

• All contain two identical catalytic α subunits with ATP binding sites

• In general P-class pumps are ion pumps that move the molecules against concentration gradient

ATP-Powered Ion Pumps

• Ionic composition of the cytosol usually differs greatly from the extracellular fluid

• Cytosolic pH is kept near 7.2 regardless of the extracellular pH

F-class and V-class Pumps

• Structures are similar to one another– Not related to P-class Pumps

• All known F and V-class pumps transport only protons

• V-class pumps maintain low pH at the cost of ATP

• F-class pumps function to power the synthesis of ATP

ABC Superfamily

• Specific to a single substrate or a family of substrates– Ions, sugars, amino acids, phospholipids,

peptides, polysaccharides, or even proteins

• Structural organization consisting of 4 domains– 2 transmembrane domains– 2 cytosolic ATP-binding domains

Summary

• Four classes of transmembrane proteins– Require the hydrolysis of ATP

• Two examples of P-class ATPases– Calcium pump of SR in muscle– Sodium Potassium pump

• Phosphorylation of the alpha subunits and a conformational change are essential for coupling ATP hydrolysis to transport ions

Summary

• V- and F-class ATPases transport protons exclusively– V-class pumps maintain pH– F-class pumps are found in mitochondria and

produce ATP

Summary

• All ABC superfamily proteins contain four core domains– 2 transmembrane domains

• Form pathway for solute movement• Determine substrate specificity

– 2 cytosolic ATP-binding domains

Summary

• ABC superfamily transport a wide array or substrates including:– Toxins– Drugs– Phospholipids– Peptides – Proteins

Summary

• According to the flippase model– Molecules diffuse into cytosolic leaflet

– Flip to exoplasmic leaflet in an ATP powered process

– Finally diffuses from membrane into extracellular space