title: Molecular dynamics simulation reveals preorganization of the chloroplast FtsY towards complex formation induced by GTP binding.
abstract: Two GTPases in the signal recognition particle (SRP) and SRP receptor (SR) interact with one another to mediate the cotranslational protein targeting pathway. Previous studies have shown that a universally conserved SRP RNA facilitates an efficient SRP-SR interaction in the presence of a signal sequence bound to SRP. However, a remarkable exception has been found in chloroplast SRP (cpSRP) pathway, in which the SRP RNA is missing. Based on biochemical and structural analyses, it is proposed that free cpSRP receptor (cpFtsY) has already been preorganized into a closed state for efficient cpSRP-cpFtsY association. However, no direct evidence has been reported to support this postulation thus far. In this study, we characterized the structural dynamics of cpFtsY and its conformational rearrangements induced by GTP binding using molecular dynamics (MD) simulations. Our results showed that the GTP-binding event triggered substantial conformational changes in free cpFtsY, including the relative orientation of N-G domain and several conserved motifs that are critical in complex formation. These rearrangements enabled the cpFtsY to relax into a preorganized 'closed' state that favored the formation of a stable complex with cpSRP54. Interestingly, the intrinsic flexibility of αN1 helix facilitated these rearrangements. In addition, GTP binding in cpFtsY was mediated by conserved residues that have been shown in other SRP GTPases. These findings suggested that GTP-bound cpFtsY could fluctuate into conformations that are favorable to form the stable complex, providing explanation of why SRP-SR interaction bypasses the requirement of the SRP RNA at a molecular level.
authors.affiliation: State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning 116023, China.
authors.forename: Ming-Jun
authors.initials: MJ
authors.lastname: Yang
authors.forename: Xue-Qin
authors.initials: XQ
authors.lastname: Pang
authors.forename: Xin
authors.initials: X
authors.lastname: Zhang
authors.forename: Ke-Li
authors.initials: KL
authors.lastname: Han
mesh_terms: D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism*; D060365:Chloroplast Proteins; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D011487:Protein Conformation; D018271:Signal Recognition Particle / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D008565:Membrane Proteins; D018271:Signal Recognition Particle; C513946:cpFtsY protein, Arabidopsis