ATP synthase (F1 portion)
ATP synthase is a chemical factory to make adenosine triphosphate (ATP). It takes a molecule of adenosine diphosphate (ADP) and a phosphate (P) group and attaches P to ADP resulting in ATP. Phosphates are phosphorous atoms with 4 oxygen atoms bound to them. ADP converts to ATP by removal of one of these 4 oxygen atoms from the phosphate resulting in a link from ADP to P by a shared oxygen. The removed oxygen combines with two hydrogen ions to form water. F1F0-ATP synthase can be found in prokaryotic (bacterial) cells and in the chloroplasts and mitochondria of eukaryotic (plants, animals) cells. It is a very large molecule with a complex organization. The F0 part of the ATP synthase sits within a lipid membrane and the flow of hydrogen ions (protons) through it generates a motion. The motion is the result of small structural changes caused by the binding and release of protons that is transmitted throughout the F0 part and further into the F1 part resulting in a large-scale motion with a frequency of about 100-200 Hz. The force generated by this motion is used to drive the synthesis of ATP from ADP and P.
The structure shown here is that of the F1 portion of the ATP synthase containing the central stalk that connects the F0 portion with the head of the F1 portion containing the catalytic (ATP-generating) subunits. The sites for binding ADP and forming ATP from them are divided into three states: open, loose and tight. In the open state ADP can easily go in and ATP out, the loose state is intermediate and the tight state has a very hight affinity for the nucleotide favoring the formation of the new phosphate bond. The motion, generated by the flow of the protons and transmitted to the F1 part through the central stalk, proceeds in steps of 120 degrees, cycling the state of the nucleotide binding sites through the 3 possible states and thus driving the synthesis of ATP.
Protein Data Bank (PDB)
author: Arno Paehler