Regulation of Structural Dynamics within a Signal Recognition Particle Promotes Binding of Protein Targeting Substrates.
Protein targeting is critical in all living organisms and involves a signal recognition particle (SRP), an SRP receptor, and a translocase. In co-translational targeting, interactions among these proteins are mediated by the ribosome. In chloroplasts, the light-harvesting chlorophyll-binding protein (LHCP) in the thylakoid membrane is targeted post-translationally without a ribosome. A multidomain chloroplast-specific subunit of the SRP, cpSRP43, is proposed to take on the role of coordinating the sequence of targeting events. Here, we demonstrate that cpSRP43 exhibits significant interdomain dynamics that are reduced upon binding its SRP binding partner, cpSRP54. We showed that the affinity of cpSRP43 for the binding motif of LHCP (L18) increases when cpSRP43 is complexed to the binding motif of cpSRP54 (cpSRP54pep). These results support the conclusion that substrate binding to the chloroplast SRP is modulated by protein structural dynamics in which a major role of cpSRP54 is to improve substrate binding efficiency to the cpSRP.
Departments of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701.
Feng
F
Gao
Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701.
Alicia D
AD
Kight
Departments of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701.
Rory
R
Henderson
Departments of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701.
Srinivas
S
Jayanthi
Departments of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701.
Parth
P
Patel
Departments of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701.
Marissa
M
Murchison
Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701.
Priyanka
P
Sharma
Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701.
Robyn L
RL
Goforth
Departments of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701. Electronic address: sthalla@uark.edu.
Thallapuranam Krishnaswamy Suresh
TKS
Kumar
Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701. Electronic address: rahenry@uark.edu.
Ralph L
RL
Henry
Departments of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701. Electronic address: cheyes@uark.edu.
Colin D
CD
Heyes
D020816:Amino Acid Motifs; D017360:Arabidopsis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D018271:Signal Recognition Particle / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020524:Thylakoids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; D018271:Signal Recognition Particle; C568473:cpSRP43 protein, Arabidopsis
chloroplast; isothermal titration calorimetry (ITC); membrane transport; molecular dynamics; protein dynamic; protein targeting; signal recognition particle (SRP); single molecule biophysics