title: Domain Organization in the 54-kDa Subunit of the Chloroplast Signal Recognition Particle.
abstract: Chloroplast signal recognition particle (cpSRP) is a heterodimer composed of an evolutionarily conserved 54-kDa GTPase (cpSRP54) and a unique 43-kDa subunit (cpSRP43) responsible for delivering light-harvesting chlorophyll binding protein to the thylakoid membrane. While a nearly complete three-dimensional structure of cpSRP43 has been determined, no high-resolution structure is yet available for cpSRP54. In this study, we developed and examined an in silico three-dimensional model of the structure of cpSRP54 by homology modeling using cytosolic homologs. Model selection was guided by single-molecule Förster resonance energy transfer experiments, which revealed the presence of at least two distinct conformations. Small angle x-ray scattering showed that the linking region among the GTPase (G-domain) and methionine-rich (M-domain) domains, an M-domain loop, and the cpSRP43 binding C-terminal extension of cpSRP54 are predominantly disordered. Interestingly, the linker and loop segments were observed to play an important role in organizing the domain arrangement of cpSRP54. Further, deletion of the finger loop abolished loading of the cpSRP cargo, light-harvesting chlorophyll binding protein. These data highlight important structural dynamics relevant to cpSRP54's role in the post- and cotranslational signaling processes.
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Rory C
authors.initials: RC
authors.lastname: Henderson
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Feng
authors.initials: F
authors.lastname: Gao
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Srinivas
authors.initials: S
authors.lastname: Jayanthi
authors.affiliation: Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Alicia
authors.initials: A
authors.lastname: Kight
authors.affiliation: Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Priyanka
authors.initials: P
authors.lastname: Sharma
authors.affiliation: Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Robyn L
authors.initials: RL
authors.lastname: Goforth
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Colin D
authors.initials: CD
authors.lastname: Heyes
authors.affiliation: Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas.
authors.forename: Ralph L
authors.initials: RL
authors.lastname: Henry
authors.affiliation: Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas. Electronic address: sthalla@uark.edu.
authors.forename: Thallapuranam Krishnaswamy
authors.initials: TK
authors.lastname: Suresh Kumar
mesh_terms: D000818:Animals; D017360:Arabidopsis; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000378:metabolism; D019843:Archaeal Proteins / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D004285:Dogs; D004926:Escherichia coli; D031541:Fluorescence Resonance Energy Transfer; D020558:GTP Phosphohydrolases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D063747:Methanocaldococcus; D056004:Molecular Dynamics Simulation; D009154:Mutation; D000072417:Protein Domains; D053838:Scattering, Small Angle; D018271:Signal Recognition Particle / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein; D048229:Sulfolobus solfataricus; D013824:Thermus; D014961:X-Ray Diffraction
chemical_list: D029681:Arabidopsis Proteins; D019843:Archaeal Proteins; D001426:Bacterial Proteins; D018271:Signal Recognition Particle; D020558:GTP Phosphohydrolases