Sandbox Reserved 344: Difference between revisions
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::::::'''THIS PAGE COPIED TO: '''[http://www.proteopedia.org/wiki/index.php/PhoP_Regulatory_Domain] | |||
{{STRUCTURE_2pl1|PDB=2pl1|SCENE=}} | {{STRUCTURE_2pl1|PDB=2pl1|SCENE=}} | ||
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=Introduction= | =Introduction= | ||
The response regulator PhoP from the OmpR/PhoB family of two-component systems is responsible for initiating the cellular response to the extracellular concentration of Mg<sup>2+</sup> of certain gram-negative bacteria such as ''Escherichia coli'' and ''Salmonella enterica''. A drop in Mg<sup>2+</sup> concentration is an indicator to the pathogenic bacteria that it has entered a host cell and needs to react correspondingly. The histidine protein kinase, PhoQ, spanning the inner membrane of the bacteria, senses the lowered Mg<sup>2+</sup> concentration and phosphorylates the cytosolic PhoP. PhoP forms a homodimer and sets a signal cascade in motion, affecting other two component signalling systems and directly regulating gene expression by binding to PhoP boxes on the DNA. PhoP consists of a regulatory domain and an effector domain. | |||
Gene regulation is achieved by the increased affinity of the homodimer to the PhoP box, a tandem repeat promoter. The response is organism specific but generally involves virulence and the survival in an environment with low Mg<sup>2+</sup> concentration. <ref name = "Bachh2007"> PMID:17545283</ref><ref name = "Groisman"> PMID:11222580</ref> | |||
=Structure= | =Structure= | ||
PhoP consists of 2 domains, the regulatory domain and the C-terminal effector domain.<ref name = "Bachh2007"/> | PhoP consists of 2 domains, the regulatory domain and the C-terminal effector domain.<ref name = "Bachh2007"/> | ||
===Regulatory Domain=== | ===Regulatory Domain=== | ||
The regulatory domain consists of 5 α-helixes and 5 β-sheets. Twofold symmetry is achieved on the α-4 helix, β-5 sheet and α-5 helix face. The regulatory domain may be phosphorylated at a conserved aspartate by PhoQ, a histidine protein kinase. Phosphorylation of this aspartate stabilizes the homodimer.<ref name = "Bachh2007"/> | The regulatory domain consists of 5 α-helixes and 5 β-sheets. Twofold symmetry is achieved on the | ||
The PhoP regulatory domain has intrinsic autophosphatase activity, allowing it to inactivate itself after a delay. | <scene name='Sandbox_Reserved_344/Dimerization_surface/1'>α-4 helix, β-5 sheet and α-5 helix face</scene> . The regulatory domain may be phosphorylated at a conserved aspartate by PhoQ, a histidine protein kinase. Phosphorylation of this aspartate stabilizes the homodimer.<ref name = "Bachh2007"/> | ||
The PhoP regulatory domain has intrinsic autophosphatase activity, allowing it to inactivate itself after a delay.<ref name = "Perron-S"> PMID:16339942</ref> | |||
=====Activated form===== | |||
:Phosphorylation of the regulatory domain stabilizes dimer formation. <ref name = "Bachh2007"/> | |||
:The phosphoryl analog <scene name='Sandbox_Reserved_344/P-analog/1'>Beryllofluoride</scene> (BeF<sup>3-</sup>) was used during crystalization of the regulatory domain of ''Escherichia coli''. | |||
:The Phosphoryl analog made the following bonds (Fluoride: light green, Magnesium: dark green): | |||
::: BeF<sup>3-</sup> | |||
::: F1 to Mg<sup>2+</sup> | |||
::: F2 to Thr 79 (Hydrogen Bond) | |||
::: F3 to Lys 101 (Salt bridge) | |||
=====Un-activated form===== | =====Un-activated form===== | ||
:Under normal physiological conditions, unactivated PhoP occurs mainly as a monomer. At higher concentration unactivated PhoP has been shown to dimerize and act | :Under normal physiological conditions, unactivated PhoP occurs mainly as a monomer. At higher concentration unactivated PhoP has been shown to dimerize and act similar to activated and dimerized PhoP. Many regulatory domains isolated from members of the OmpR/PhoB family and in their inactive form, crystalize in a form similar to their activated dimers.<ref name = "Bachh2007"/> | ||
===Effector domain=== | ===Effector domain=== | ||
When the regulatory domain is phosphorylated, PhoP forms a homodimer. There is no direct change in conformation conferred on the effector domain by the regulatory domain. It is the dimerization that activates the effector domain. The PhoP has a winged helix-turn-helix motif characteristic of the OmpR/PhoB family of response regulators.<ref name = "Hickey"> PMID:19652341</ref> This winged helix-turn-helix allows binding to DNA and regulation of transcription. Binding occurs at tandem repeat promoters with two repeats of the sequence (T/G)GTTTA, known as the PhoP box.<ref name = "Groisman"/> | |||
=Function= | =Function= | ||
Two component systems allow bacteria to respond to changes in their environment. These systems are found mainly in prokaryotes and a few eukaryotes.<ref name = "Mack"> PMID:19371748</ref> The PhoP/PhoQ system, found specifically in gram-negative bacteria, react mainly to a drop in extracellular Mg<sup>2+</sup>. Since the magnesium concentration is typically lower inside the host cell compared to outside, this acts as a trigger to become virulent. Other functions activated by the PhoP/PhoQ system includes adaptation to low Mg<sup>2+</sup> conditions, changes in cell wall, expression of proteases to protect against antimicrobial peptides and various other species specific responses. PhoP in ''Salmonella enterica'' regulates up to 40 proteins.<ref name = "Groisman"/> | Two component systems allow bacteria to respond to changes in their environment. These systems are found mainly in prokaryotes and a few eukaryotes.<ref name = "Mack"> PMID:19371748</ref> The PhoP/PhoQ system, found specifically in gram-negative bacteria, react mainly to a drop in extracellular Mg<sup>2+</sup>. Since the magnesium concentration is typically lower inside the host cell compared to outside, this acts as a trigger to become virulent. Other functions activated by the PhoP/PhoQ system includes adaptation to low Mg<sup>2+</sup> conditions, changes in cell wall, expression of proteases to protect against antimicrobial peptides and various other species specific responses. PhoP in ''Salmonella enterica'' regulates up to 40 proteins.<ref name = "Groisman"/> | ||
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Further evidence to PhoP's role in response to the extracellular environment is given by evidence of sRNA regulation of the expression of the phoP gene. Envelope stress, though σ<sup>E</sup> and the sRNA MicA affects expression of the PhoPQ system. <ref name = "Coornaert"> PMID:20345657</ref> | Further evidence to PhoP's role in response to the extracellular environment is given by evidence of sRNA regulation of the expression of the phoP gene. Envelope stress, though σ<sup>E</sup> and the sRNA MicA affects expression of the PhoPQ system. <ref name = "Coornaert"> PMID:20345657</ref> | ||
The PhoP/PhoQ system may also be found in non-cytoplasmic pathogens, such as ''Erwinia carotovora supsb. carotovora'', a plant pathogen living in the intercellular fluid, or non-pathogenic bacteria. <ref name = "Groisman"/> | |||
=Importance of PhoP= | =Importance of PhoP= | ||
PhoP/PhoQ plays in key role in certain bacteria becoming virulent. This makes it a promising target for vaccine and antimicrobial drug development. | PhoP/PhoQ plays in key role in certain bacteria becoming virulent. For example, ''Salmonella typhimurium'' becomes avirulent when it carries a phoP mutation.<ref name = "Groisman1989"> PMID:2674945</ref> This makes it a promising target for vaccine and antimicrobial drug development.<ref name = "Bachh2007"/> | ||
=References= | =References= | ||
<references/> | <references/> | ||