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Updated: Aug 15, 2026

Combining Chemical Cross-linking and Mass Spectrometry of Intact Protein Complexes to Study the Architecture of Multi-subunit Protein Assemblies
Published on: November 28, 2017
Three-dimensional solution structures of the chromodomains of cpSRP43
Vaithiyalingam Sivaraja1, Thallapuranam Krishnaswamy Suresh Kumar, Philominathan Sagaya Theresa Leena
1Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, Arkansas 72701, USA.
Abstract:
Chloroplasts contain a unique signal recognition particle (cpSRP). Unlike the cytoplasmic forms, the cpSRP lacks RNA but contains a conserved 54-kDa GTPase and a novel 43-kDa subunit (cpSRP43). Recently, three functionally distinct chromodomains (CDs) have been identified in cpSRP43. In the present study, we report the three-dimensional solution structures of the three CDs (CD1, CD2, and CD3) using a variety of triple resonance NMR experiments. The structure of CD1 consists of a triple-stranded beta-sheet segment. The C-terminal helical segment typically found in the nuclear chromodomains is absent in CD1. The secondary structural elements in CD2 and CD3 include a triple-stranded antiparallel beta-sheet and a C-terminal helix. Interestingly, the orientation of the C-terminal helix is significantly different in the structures of CD2 and CD3. Critical comparison of the structures of the chromodomains of cpSRP43 with those found in nuclear chromodomain proteins revealed that the diverse protein-protein interactions mediated by the CDs appear to stem from the differences that exist in the surface charge potentials of each CD. Results of isothermal titration calorimetry experiments confirmed that only CD2 is involved in binding to cpSRP54. The negatively charged C-terminal helix in CD2 possibly plays a crucial role in the cpSRP54-cpSRP43 interaction.
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