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Results 1 - 6 of 6
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General Information
in prokaryotic cells, the signal recognition particle consists of a SRP54 protein or Ffh and a 4.5S SRP RNA. Ffh contains a methionine-rich M domain, which binds the SRP RNA and the signal sequence on the translating ribosome. In addition, an NG domain in Ffh, comprising a GTPase G domain and a four-helix bundle N domain, forms a tight complex with a highly homologous NG domain in the SRP receptor, called FtsY in bacteria, in the presence of GTP. GTP hydrolysis at the end of the signal recognition particle cycle drives the disassembly of the Ffh-FtsY GTPase complex. The assembly of the signal recognition particle-FtsY GTPase complex and its GTPase activation require discrete conformational rearrangements in the signal recognition particle that are regulated by the RNC and the target membrane, respectively, thus ensuring the spatial and temporal precision of these molecular events during protein targeting, function of SRP RNA during co-translational protein targeting, overiew
bidentate interaction between the Ffh-FtsY GTPase complex and the distal end of the SRP RNA, overview. By modifying the GTPase docking interface, the efficiency of activation of the Ffh-FtsY GTPase complex can be specifically tuned. A guanine at residue 86 could compete with and substitute for G83 as a catalytic base. Conserved bases in loop D specifically catalyze GTP hydrolysis, a guanine at residue 86 can compete with and substitute for G83 as a catalytic base, loop E controls the action of the distal end docking sites
concerted complex assembly and GTPase activation occurs in the chloroplast signal recognition particle. In contrast to the cytosolic homologues, GTPase activation in the chloroplast SRP-SR complex contributes marginally to the targeting of LHC proteins. Complex assembly and GTPase activation are highly coupled in the chloroplast SRP and SR and suggest that the chloroplast GTPases may forego the GTPase activation step as a key regulatory point. Homology model of the cpSRP54·cpFtsY complex based on superposition of the crystal structure of apo-cpFtsY onto that of Thermus aquaticus SR, i.e. FtsY, in complex with Ffh. Thermodynamic and kinetics for formation of the cpSRP54-cpFtsY complex, formed by wild-types and mutants, detailed overview. IBD loops play essential roles in both complex assembly and GTPase activation
physiological function
the enzyme is involved in translocation of the signal recognition particle (SRP) RNA is a universally conserved and essential component of the SRP that mediates the co-translational targeting of proteins to the correct cellular membrane. During the targeting reaction, two functional ends in the signal recognition particle RNA mediate distinct functions. Whereas the RNA tetraloop facilitates initial assembly of two GTPases between the signal recognition particle and signal recognition particle receptor, this GTPase complex subsequently relocalizes about 100 A to the 5',3'-distal end of the RNA, a conformation crucial for GTPase activation and cargo handover
physiological function
the universally conserved signal recognition particle, SRP, and SRP receptor, SR, mediate the cotranslational targeting of proteins to cellular membranes. In contrast, a unique chloroplast SRP in green plants is primarily dedicated to the post-translational targeting of light harvesting chlorophyll a/b binding proteins. In both pathways, dimerization and activation between the SRP and SR GTPases mediate the delivery of cargo. Efficient assembly of the cpSRP54-cpFtsY complex is crucial for the targeting and integration of LHCP, whereas GTPase activation and/or GTP hydrolysis plays a modulatory role to help enhance the efficiency of targeting
physiological function
together with its receptor SR, signal recognition particle, SRP, mediates the GTP-dependent delivery of translating ribosomes bearing signal sequences to translocons on the target membrane. The activated SRP:SR GTPase complex binds the distal end of the SRP hairpin RNA where GTP hydrolysis is stimulated. The SRP:SR GTPase complex initially assembles at the tetraloop end of the SRP RNA and then relocalizes to the opposite end of the RNA. This rearrangement provides a mechanism for coupling GTP hydrolysis to the handover of cargo to the translocon
Results 1 - 6 of 6