RT Journal Article SR Electronic T1 Small-angle neutron scattering solution structures of NADPH-dependent sulfite reductase JF bioRxiv FD Cold Spring Harbor Laboratory SP 2020.12.08.415968 DO 10.1101/2020.12.08.415968 A1 Murray, Daniel T. A1 Weiss, Kevin L. A1 Stanley, Christopher B. A1 Nagy, Gergely A1 Stroupe, M. Elizabeth YR 2020 UL http://biorxiv.org/content/early/2020/12/08/2020.12.08.415968.abstract AB Sulfite reductase (SiR), a dodecameric complex of flavoprotein reductase subunits (SiRFP) and hemoprotein oxidase subunits (SiRHP), reduces sulfur reduction for biomass incorporation. Electron transfer within SiR requires intra- and inter-subunit interactions that are mediated by the relative position of each protein, governed by flexible domain movements. Using small-angle neutron scattering, we report the first solution structures of SiR heterodimers containing a single copy of each subunit. These structures show how the subunits bind and how both subunit binding and oxidation state impact SiRFP’s conformation. Neutron contrast matching experiments on selectively deuterated heterodimers allow us to define the contribution of each subunit to the solution scattering. SiRHP binding induces a change in the position of SiRFP’s flavodoxin-like domain relative to its ferredoxin-NADP+ reductase domain while compacting SiRHP’s N-terminus. Reduction of SiRFP leads to a more open structure relative to its oxidized state, re-positioning SiRFP’s N-terminal flavodoxin-like domain towards the SiRHP binding position. These structures show, for the first time, how both SiRHP binding to, and reduction of, SiRFP positions SiRFP for electron transfer between the subunits.