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Combining X-Ray Crystallography with Small Angle X-Ray Scattering to Model Unstructured Regions of Nsa1 from S. Cerevisiae
Published on: January 10, 2018
A helix swapping study of two protein cages
Rongli Fan1, Aimee L Boyle, Vee Vee Cheong
1Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371.
Investigating protein cage assembly, this study found that the E helix, not the BC helix, is crucial for self-assembly. Mutants revealed new insights into protein nanostructure formation and design.
Area of Science:
- Biochemistry
- Structural Biology
- Materials Science
Background:
- Protein cages are versatile structures used in drug delivery, materials science, and studying confined reactions.
- Two key protein cages, DPS and BFR, share structural similarities but differ in an additional short helix.
- This extra helix's role in self-assembly into distinct cage symmetries (12-mer and 24-mer) was previously unclear.
Purpose of the Study:
- To investigate the role of short additional helices in the self-assembly of DPS and BFR protein cages.
- To determine if these minidomains are critical for forming higher-order cage structures.
- To explore the potential for engineering novel protein cages through domain manipulation.
Main Methods:
- Site-directed mutagenesis to delete and swap key helical minidomains in DPS and BFR.
- Circular dichroism spectroscopy to assess protein structure and thermal stability.
- Dynamic light scattering, size exclusion chromatography, and sedimentation equilibrium to analyze self-assembly and oligomer formation.
Main Results:
- Mutant proteins retained helical structures and cooperative unfolding.
- Many BFR mutants failed to self-assemble into cages, forming lower-order complexes.
- Several DPS mutants successfully formed cages, indicating the E helix is more critical than the BC helix for assembly.
- Fusing a BFR minidomain to DPS created a novel, larger 12-subunit cage.
Conclusions:
- The E helix plays a more significant role in protein cage self-assembly than the BC helix.
- Dimerization may be less critical for nanostructure formation than previously hypothesized.
- Protein cage engineering is feasible, allowing for the creation of novel structures with altered properties.
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