Nitrogenase: Difference between revisions
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Two different proteins comprise the nitrogenase complex. The FeMo protein binds substrate and reduces H<sup>+</sup> and N<sub>2</sub> to H<sub>2</sub> and ammonia, while the Fe protein receives electrons from ferredoxin, hydrolyzes ATP, and reduces the FeMo protein. To the right is shown a crystal structure (PDB entry [[1n2c]]) where two complexes of FeMo protein bound to Fe protein were crystallized together. Click here to see only <scene name='Sandbox_10/1n2c_single_complex/2'>one complex</scene>. | Two different proteins comprise the nitrogenase complex. The FeMo protein binds substrate and reduces H<sup>+</sup> and N<sub>2</sub> to H<sub>2</sub> and ammonia, while the Fe protein receives electrons from ferredoxin, hydrolyzes ATP, and reduces the FeMo protein. To the right is shown a crystal structure (PDB entry [[1n2c]]) where two complexes of FeMo protein bound to Fe protein were crystallized together. Click here to see only <scene name='Sandbox_10/1n2c_single_complex/2'>one complex</scene>. | ||
At the bottom of the protein, where the Fe protein comes into contact with the FeMo protein, is a <scene name='Sandbox_10/1n2c_fes_cluster_cys/1'>4Fe:4S cluster</scene>, held in place by cysteines. This cluster accepts electrons from ferredoxin and gives electrons to the FeMo protein. | The <scene name='Sandbox_10/1n2c_fe_protein/1'>Fe protein</scene> is here bound to two <scene name='Sandbox_10/1n2c_atp/3'>ADP x AlF<sub>4</sub><sup>-</sup></scene>, an analog for the planar transition state of ATP hydrolysis. The motif that binds ATP is a conserved nucleotide binding motif called Walker's motif A. Coloring by <scene name='Sandbox_10/1n2c_atp_evolutionary/1'>evolutionary conservation</scene>, the nucleotide binding pocket is clear. At the bottom of the protein, where the Fe protein comes into contact with the FeMo protein, is a <scene name='Sandbox_10/1n2c_fes_cluster_cys/1'>4Fe:4S cluster</scene>, held in place by cysteines. This cluster accepts electrons from ferredoxin and gives electrons to the FeMo protein. | ||
When the Fe protein is bound to the FeMo protein (<scene name='Sandbox_10/1n2c_single_complex/2'>zoom out</scene>), ATP is hydrolyzed and electrons that were transferred to the 4Fe:4S cluster of the Fe protein by ferredoxin are transferred to the FeMo protein. The crystal structure of the complete nitrogenase complex reveals how the binding of the Fe and FeMo proteins, the hydrolysis of ATP, and the transfer of electrons are all coupled. The figure below summarizes how these processes are linked. | When the Fe protein is bound to the FeMo protein (<scene name='Sandbox_10/1n2c_single_complex/2'>zoom out</scene>), ATP is hydrolyzed and electrons that were transferred to the 4Fe:4S cluster of the Fe protein by ferredoxin are transferred to the FeMo protein. The crystal structure of the complete nitrogenase complex reveals how the binding of the Fe and FeMo proteins, the hydrolysis of ATP, and the transfer of electrons are all coupled. The figure below summarizes how these processes are linked. | ||
[[Image:clip_image002.jpg]] | [[Image:clip_image002.jpg]] | ||
Before this crystal structure showing the complete nitrogenase complex was solved, crystal structures of the Fe and FeMo proteins had been solved, but the mechanisms of ATP hydrolysis and electron transfer were still unknown. In this structure, as indicated in the figure above, the two subunits of the Fe protein were observed to have swung closer together. This movement results from Fe protein binding to FeMo protein. Focusing in on the <scene name='Sandbox_10/1n2c_atp/3'>ATP binding pocket</scene> discussed above, especially on the <scene name='Sandbox_10/1n2c_atp_lys_10/1'>AlF<sub>4</sub><sup>-</sup></scene> that is an analog for the negatively charged planar transition state of phosphate hydrolysis | |||