Consensus model of a cyanobacterial light-dependent protochlorophyllide oxidoreductase in its pigment-free apo-form and photoactive ternary complex

Commun Biol. 2019 Sep 25:2:351. doi: 10.1038/s42003-019-0590-4. eCollection 2019.

Abstract

Photosynthetic organisms employ two different enzymes for the reduction of the C17 = C18 double bond of protochlorophyllide (Pchlide), yielding the chlorophyll precursor chlorophyllide. First, a nitrogenase-like, light-independent (dark-operative) Pchlide oxidoreductase and secondly, a light-dependent Pchlide oxidoreductase (LPOR). For the latter enzyme, despite decades of research, no structural information is available. Here, we use protein structure modelling, molecular dynamics (MD) simulations combined with multi-wavelength analytical ultracentrifugation (MWA-AUC) and small angle X-ray scattering (SAXS) experiments to derive a consensus model of the LPOR apoprotein and the substrate/cofactor/LPOR ternary complex. MWA-AUC and SAXS experiments independently demonstrate that the apoprotein is monomeric, while ternary complex formation induces dimerization. SAXS-guided modelling studies provide a full-length model of the apoprotein and suggest a tentative mode of dimerization for the LPOR ternary complex, supported by published cross-link constraints. Our study provides a first impression of the LPOR structural organization.

Keywords: Bacterial structural biology; Molecular conformation; Oxidoreductases; SAXS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apoproteins / chemistry
  • Apoproteins / metabolism
  • Cyanobacteria / physiology*
  • Models, Molecular
  • Molecular Structure
  • Oxidoreductases Acting on CH-CH Group Donors / chemistry
  • Oxidoreductases Acting on CH-CH Group Donors / metabolism*
  • Photosynthesis*
  • Pigments, Biological / chemistry
  • Pigments, Biological / metabolism*
  • Protein Multimerization
  • Structure-Activity Relationship

Substances

  • Apoproteins
  • Pigments, Biological
  • Oxidoreductases Acting on CH-CH Group Donors
  • protochlorophyllide reductase