Low-resolution structures of transient protein-protein complexes using small-angle X-ray scattering

Area of Science:

• Biophysics
• Structural Biology
• Biochemistry

Background:

• Studying weak protein-protein complexes in solution is challenging.
• Small-angle X-ray scattering (SAXS) is a powerful technique for structural analysis.
• Deconvoluting signals from coexisting species is crucial for accurate structural determination.

Purpose of the Study:

• To determine the low-resolution structures of monomeric and dimeric low molecular weight phosphatase (lmwPTP) in solution.
• To demonstrate the utility of SAXS combined with multivariate curve resolution with alternating least squares (MCR-ALS) for weak complex analysis.
• To validate the method against crystallographic data and NMR measurements.

Main Methods:

• Utilized small-angle X-ray scattering (SAXS) on an oligomerization equilibrium of lmwPTP.
• Applied the multivariate curve resolution with alternating least squares (MCR-ALS) algorithm to deconvolute SAXS data.
• Compared derived structures with crystallographic data and dissociation constants with NMR measurements.

Main Results:

• Successfully determined individual low-resolution structures of monomeric and dimeric lmwPTP.
• The dimeric complex constituted a maximum of 15% of macromolecules in the sample.
• Derived structures showed good agreement with crystallographic data, and dissociation constants matched NMR results.

Conclusions:

• SAXS coupled with MCR-ALS is effective for studying transient biomolecular complexes in solution.
• The method can resolve structures of components present at low concentrations (e.g., 15%).
• The approach provides a robust framework for analyzing oligomerization equilibria and weak interactions.