Small-angle neutron scattering solution structures of NADPH-dependent sulfite reductase

Area of Science:

• Biochemistry
• Structural Biology
• Microbiology

Background:

• Sulfite reductase (SiR) is a crucial enzyme complex for sulfur assimilation in biomass.
• Electron transfer within SiR relies on precise subunit positioning and flexible domain movements.

Purpose of the Study:

• To determine the solution structures of SiR heterodimers using small-angle neutron scattering.
• To elucidate how subunit binding and redox state influence SiRFP conformation and inter-subunit electron transfer.

Main Methods:

• Small-angle neutron scattering (SANS) on SiR heterodimers.
• Neutron contrast matching experiments on selectively deuterated heterodimers.

Main Results:

• The first solution structures of SiR heterodimers (SiRFP-SiRHP) were determined.
• SiRHP binding alters SiRFP's flavodoxin-like domain position and compacts SiRHP's N-terminus.
• SiRFP reduction results in a more open structure, positioning the N-terminal domain for SiRHP interaction.

Conclusions:

• SiRHP binding and SiRFP reduction dynamically position subunits for efficient electron transfer.
• These findings provide novel insights into the structural mechanisms governing sulfite reductase activity.