Small-angle neutron scattering from native and irradiated superoxide dismutase in aqueous solution

Area of Science:

• Biochemistry
• Structural Biology
• Enzymology

Background:

• Bovine erythrocyte superoxide dismutase (SOD) is a crucial enzyme for cellular defense against reactive oxygen species.
• Understanding the structural dynamics of both holo (metal-bound) and apo (metal-free) forms is essential for elucidating its function.
• Previous studies have not fully characterized the solution structure and aggregation behavior of this enzyme under various conditions.

Purpose of the Study:

• To determine the approximate size and shape of holo and apo bovine erythrocyte superoxide dismutase using small-angle neutron scattering.
• To investigate the effect of gamma irradiation on the aggregation state of superoxide dismutase.
• To analyze the interactions between apo and holo forms and the stability of radiation-induced aggregates.

Main Methods:

• Small-angle neutron scattering (SANS) on aqueous solutions of holo and apo bovine erythrocyte superoxide dismutase at neutral pH.
• Analysis of scattering data using a cylindrical model to determine the radius of gyration (Rg).
• Gamma irradiation of enzyme solutions at varying doses and concentrations, followed by SANS and High-Performance Liquid Chromatography (HPLC) analysis.

Main Results:

• Both holo and apo forms of bovine erythrocyte superoxide dismutase fit a cylindrical model, with the apoenzyme showing a marginally larger radius of gyration.
• Gamma irradiation induced side-by-side aggregation of superoxide dismutase molecules, with potential end-to-end stacking at higher doses and concentrations.
• HPLC data confirmed interactions between apo and holo forms and demonstrated the dissociation of radiation-induced aggregates.

Conclusions:

• Small-angle neutron scattering provides insights into the solution structure and aggregation of bovine erythrocyte superoxide dismutase.
• Gamma irradiation is a potent inducer of superoxide dismutase aggregation, with structural interpretations becoming complex at high doses.
• The apo and holo forms of superoxide dismutase interact, and radiation-induced aggregates are reversible, suggesting dynamic structural properties.