SecA: Difference between revisions

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=Introduction=

The [http://www.nature.com/nature/journal/v455/n7215/full/nature07335.html SecA] ATPase '''SecA''' drives the post-translational translocation of proteins through the SecY channel in the bacterial inner membrane. SecA is a dimer that can dissociate into monomers under certain conditions. Many bacterial proteins are transported post-translationally across the inner membrane by the Sec machinery, which consists of two essential components (1-4). One is the SecY complex, which forms a conserved heterotrimeric protein-conducting channel in the inner membrane.<ref name=journal1>PMID:15618215</ref> The other is SecA, a cytoplasmic ATPase, which "pushes" substrate polypeptide chains through the SecY channel.<ref name=journal1/> . For additional details see [[SecA PBD motions]].

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Here we report crystal structures of SecA bound in an intermediate state of nucleotide hydrolysis to the SecY channel. The structures suggest mechanisms for how the channel is opened and prepared for the arrival of a translocation substrate, and how SecA moves polypeptides through the channel.

Notable finding is that ADP binding to the high-affinity site stabilizes a compact conformation of SecA (ground state) that has low affinity for the SecYEG/membrane<ref name=journal1/>. Click the green link to view the active site of <scene name='~~Sandbox_158~~/~~Scene_1~~/3'>ADP</scene> with surrounding amino acids. This result suggests that following ATP hydrolysis, the ADP-bound SecA undergoes retraction from the translocon to complete one reaction cycle. However, the apo (nucleotide free) form of SecA can also exist in a compact conformation with low affinity for the translocon<ref name=journal1/>. Moreover, ADP release from SecA is stimulated by SecYEG/membrane, raising the question whether SecA retraction from the membrane occurs in the ADP-bound form, the apo form, or both<ref name=journal1/>.

Notable finding is that ADP binding to the high-affinity site stabilizes a compact conformation of SecA (ground state) that has low affinity for the SecYEG/membrane<ref name=journal1/>. Click the green link to view the active site of <scene name='38/382930/Cv/3'>ADP</scene> with surrounding amino acids (Water molecules shown as red spheres). This result suggests that following ATP hydrolysis, the ADP-bound SecA undergoes retraction from the translocon to complete one reaction cycle. However, the apo (nucleotide free) form of SecA can also exist in a compact conformation with low affinity for the translocon<ref name=journal1/>. Moreover, ADP release from SecA is stimulated by SecYEG/membrane, raising the question whether SecA retraction from the membrane occurs in the ADP-bound form, the apo form, or both<ref name=journal1/>.

==Structure Determination Of SecA-SecY Complexes==

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-<StructureSection load='3jv2' size='400' side='right' scene='' caption='Dimer of monomeric SecA complex with peptide (pink and yellow), ADP and Mg+2 ion (green), [[3jv2]]'>
+<StructureSection load='3jv2' size='400' side='right' scene='' caption='Dimer of monomeric SecA complex with peptide (pink and yellow), ADP and Mg+2 ion (green), [[3jv2]]' pspeed='8'>
 =Introduction=
 The [http://www.nature.com/nature/journal/v455/n7215/full/nature07335.html SecA] ATPase '''SecA''' drives the post-translational translocation of proteins through the SecY channel in the bacterial inner membrane. SecA is a dimer that can dissociate into monomers under certain conditions. Many bacterial proteins are transported post-translationally across the inner membrane by the Sec machinery, which consists of two essential components (1-4). One is the SecY complex, which forms a conserved heterotrimeric protein-conducting channel in the inner membrane.<ref name=journal1>PMID:15618215</ref> The other is SecA, a cytoplasmic ATPase, which "pushes" substrate polypeptide chains through the SecY channel.<ref name=journal1/> .  For additional details see [[SecA PBD motions]].
@@ Line 7: / Line 7: @@
 Here we report crystal structures of SecA bound in an intermediate state of nucleotide hydrolysis to the SecY channel. The structures suggest mechanisms for how the channel is opened and prepared for the arrival of a translocation substrate, and how SecA moves polypeptides through the channel.
-Notable finding is that ADP binding to the high-affinity site stabilizes a compact conformation of SecA (ground state) that has low affinity for the SecYEG/membrane<ref name=journal1/>. Click the green link to view the active site of <scene name='Sandbox_158/Scene_1/3'>ADP</scene> with surrounding amino acids. This result suggests that following ATP hydrolysis, the ADP-bound SecA undergoes retraction from the translocon to complete one reaction cycle. However, the apo (nucleotide free) form of SecA can also exist in a compact conformation with low affinity for the translocon<ref name=journal1/>. Moreover, ADP release from SecA is stimulated by SecYEG/membrane, raising the question whether SecA retraction from the membrane occurs in the ADP-bound form, the apo form, or both<ref name=journal1/>.
+Notable finding is that ADP binding to the high-affinity site stabilizes a compact conformation of SecA (ground state) that has low affinity for the SecYEG/membrane<ref name=journal1/>. Click the green link to view the active site of <scene name='38/382930/Cv/3'>ADP</scene> with surrounding amino acids (Water molecules shown as red spheres). This result suggests that following ATP hydrolysis, the ADP-bound SecA undergoes retraction from the translocon to complete one reaction cycle. However, the apo (nucleotide free) form of SecA can also exist in a compact conformation with low affinity for the translocon<ref name=journal1/>. Moreover, ADP release from SecA is stimulated by SecYEG/membrane, raising the question whether SecA retraction from the membrane occurs in the ADP-bound form, the apo form, or both<ref name=journal1/>.
 ==Structure Determination Of SecA-SecY Complexes==