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Novel bacterial clade reveals origin of form I Rubisco.

  • Author(s): Banda, Douglas M;
  • Pereira, Jose H;
  • Liu, Albert K;
  • Orr, Douglas J;
  • Hammel, Michal;
  • He, Christine;
  • Parry, Martin AJ;
  • Carmo-Silva, Elizabete;
  • Adams, Paul D;
  • Banfield, Jillian F;
  • Shih, Patrick M
  • et al.
Abstract

Rubisco sustains the biosphere through the fixation of CO2 into biomass. In plants and cyanobacteria, form I Rubisco is structurally comprised of large and small subunits, whereas all other Rubisco forms lack small subunits. The rise of the form I complex through the innovation of small subunits represents a key, yet poorly understood, transition in Rubisco's evolution. Through metagenomic analyses, we discovered a previously uncharacterized clade sister to form I Rubisco that evolved without small subunits. This clade diverged before the evolution of cyanobacteria and the origin of the small subunit; thus, it provides a unique reference point to advance our understanding of form I Rubisco evolution. Structural and kinetic data presented here reveal how a proto-form I Rubisco assembled and functioned without the structural stability imparted from small subunits. Our findings provide insight into a key evolutionary transition of the most abundant enzyme on Earth and the predominant entry point for nearly all global organic carbon.

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