Receiver domain of sensor histidine kinase CKI1: Difference between revisions
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<StructureSection load='3mmn' size='400' side='right' caption='Magnesium-bound form of CKI1RD, (PDB entry [[3mmn]])' scene='Receiver_domain/Initial_1/2'> | |||
[[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]] | [[Image:Receiver_domain_surf.png|250px|left|thumb| Receiver domain of CKI1 from ''Arabidopsis'', [[3mmn]]]] | ||
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'''Receiver domain of sensor histidine kinase CKI1''' (CKI1RD) catalyses the transphosphorylation reaction during hormonal and abiotic signalling in plants. Membrane-bound histidine kinase Cytokinin-independet 1 '''(CKI1)''' is a member of the Multistep phosphorelay '''(MSP)''' signalling pathway in ''Arabidopsis''. CKI1 was found to be constitutively active activator of a cytokinin-like response. Intracellularly located C-terminal CKI1RD is responsible for the recognition of CKI1 downstream signalling partners from family of Arabidopsis histidine-containing phosphotransfer proteins '''(AHP)''' and triggers the cytokinin-like signal transmission. Divalent magnesium ion bound in the active site of CKI1RD is essential for the transphosphorylation reaction. Crystal structure of CKI1RD was determined as magnesium-free and magnesium-bound form. Magnesium binding induces the rearrangement of residues around the active site of CKI1RD, as was determined by both X-ray crystallography and NMR spectroscopy. | |||
== Biological Function == | == Biological Function == | ||
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Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs. | Cytokinin signalling in plants is triggered by MSP<ref>PMID:10664616</ref> , which was adopted by plants from bacterial Two-component system<ref>PMID:12226482</ref>. The signalling molecule is bound to the sensory histidin-kinase and then is transferred via AHPs (AHP1-AHP5) to nuclear response regulators (ARRs). ARRs act as transcription factors or interact with other effector proteins<ref>PMID:12972049</ref> to perform specific cellular response to initial environmental stimuli. In contrast to ancestral Two-component signalling in bacteria, protein interactions in plant MSP are supposed to be rather nonspecific. The current MSP interaction maps from ''Arabidopsis'' are based on yeast two-hybrid system<ref>PMID:10930573</ref><ref>PMID: 16965536</ref><ref>PMID:18642946</ref> and show the AHPs as highly promiscuous, able to interact with all cytokinin receptors, number of other histidine-kinases and number of ARRs. | ||
Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>. | Recently was shown that CKI1RD is responsible for a specific interaction with individual subset of second messengers from AHP family (AHP2, AHP3, AHP5)<ref>PMID:21569135</ref>. | ||
==CKI1RD structure and effects of magnesium binding in the active site== | ==CKI1RD structure and effects of magnesium binding in the active site== | ||
The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. | The crystal structure of CKI1RD shows the conformational conservation of RDs belonging to CheY-like protein superfamily <ref>PMID:8257674</ref><ref>PMID:19036790</ref>. CKI1RD is folded in a (α/β)5 manner with central β-sheet formed from parallel beta-strands (β2-β1-β3-β4-β5) surrounded on both sides by two (α1 and α5) and three (α2, α3, α4) α-helices. Secondary structure elements are connected by five loops L1-L5 on the face side of the protein. The active site with <scene name='Receiver_domain/Initial_1/6'> phosphoacceptor D1050</scene> is located at the C-termini of the central β3-strand in a pocket delineated loops L1, L3 and L5. A highly conserved <scene name='Receiver_domain/Initial_1/4'> triad of carboxyl oxygens</scene>, formed by D1050 together with D992 and D993 and carbonyl oxygen of <scene name='Receiver_domain/Initial_1/8'> Q1052</scene> give the active site an acidic character. This architecture of the active site is well conserved among CheY-like superfamily and corresponds to the phosphotransfer function of the receiver domains. | ||
[[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Structure and sequence conservation among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains (CKI1RD numbering)]] | [[Image:Structural and sequentional conservation among receiver domains.png.PNG|250px|left|thumb| Structure and sequence conservation among known receiver domains. Left: Superimposition of 35 known crystal structures of receiver domains. Right: Representation of highly conserved residues among receiver domains (CKI1RD numbering)]] | ||