Mega-Dalton protein complexes characterization

Significance of the Topic

Large megadalton protein complexes such as bacteriophage baseplates are crucial for understanding phage–host interactions. Detailed solution-state analyses of these assemblies inform structural biology and the development of novel antiviral strategies.

Objectives and Study Overview

This work presents an integrated analytical SEC platform combined with multi-angle light scattering (MALS), quasi-elastic light scattering (QELS), refractometry and UV280 nm absorbance to characterize the TP901-1 lactococcal phage baseplate. Two target assemblies were investigated:

• The BppU–BppL subcomplex
• The full BppU–BppL–Dit megadalton assembly

Methodology and Instrumentation

Recombinant co-expression generated defined protein mixtures. Separation by size-exclusion chromatography on Superose 6 10/30 or Shodex KW804 columns was monitored on-line by:

• MALS for absolute molar mass determination
• QELS for hydrodynamic radius (Rh)
• Refractometry for concentration measurement
• UV280 nm absorbance for protein detection

Data analysis yielded molar mass, radius of gyration (Rg) and Rh values.

Main Results and Discussion

• BppL behaved as a homotrimer in solution, consistent with crystallographic data.
• The BppU–BppL assembly comprised nine BppL and three BppU units (~600 kDa).
• Inclusion of Dit produced a 1.7 MDa complex with 54 BppL, 18 BppU and 6 Dit copies, characterized by Rh = 12.5 nm and Rg = 11.4 nm.
• The high valency of receptor binding proteins suggests avidity-driven enhancement of host anchoring.

Benefits and Practical Applications

This SEC-MALS/QELS approach allows precise in-solution determination of stoichiometry and size for large macromolecular assemblies, supporting structural analyses and guiding the design of phage-based therapeutics or nanobiomaterials.

Future Trends and Potential Applications

Future directions include integration with native mass spectrometry, high-resolution cryo-EM correlation and automated high-throughput workflows. These enhancements will extend applicability to diverse supramolecular systems and dynamic assembly processes.

Conclusion

The described method reliably characterizes MegaDalton protein complexes in solution, providing detailed stoichiometry and structural parameters. It represents the largest bacteriophage baseplate assembly analyzed to date by this approach.

Used Instrumentation

• Wyatt Technology DAWN MALS detector
• QELS module
• Optilab refractometer
• UV280 nm absorbance detector
• Superose 6 10/30 and Shodex KW804 SEC columns

References

• Veesler D. Note on TP901-1 phage baseplate characterization, Wyatt Technology Corporation, 2016.