Background
Chloroplasts are the photosynthetic organelles that convert light energy into chemical energy. They retain their own genome (the plastid genome), which is transcribed by a bacterial-type RNA polymerase called PEP (Plastid-Encoded RNA Polymerase). Understanding PEP is critical for crop improvement and bioenergy research.
The Challenge
- Complex assembly: PEP is a multi-subunit complex (>500 kDa) with associated transcription factors
- Plant source: The complex was isolated from plant tissue, yielding limited material
- Conformational heterogeneity: Multiple transcription states coexist
- Novel architecture: No homologous structure had been solved previously
Shuimu's Approach
- Native complex purification: PEP was isolated from spinach chloroplasts using a multi-step chromatography protocol
- GraFuture™ graphene oxide grids: Essential for achieving uniform particle distribution
- High-throughput data collection: Multiple sessions on 300kV Titan Krios, generating >10,000 micrographs
- 3D classification: Extensive classification to separate transcription initiation, elongation, and termination states
- First atomic structure of the plant plastid RNA polymerase complex
- Revealed the unique architecture of PEP-associated proteins (PAPs)
- Showed how sigma factors recruit PEP to chloroplast promoters
- Captured multiple transcription cycle intermediates
Results
Impact
This structure provides a molecular blueprint for understanding how plants regulate photosynthesis gene expression. It opens avenues for engineering chloroplast gene expression to improve crop yield and stress tolerance.
Recognition
Featured on the cover of Cell (March 2024) — one of the highest-profile recognitions in structural biology.
Publication
Cryo-EM structures of the plant plastid-encoded RNA polymerase — Cell (Cover), March 2024. Read the paper →