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Fig. 36: a) Cryo-EM reconstruction of the NosRcaΔC-Rubisco complex. A side-view aligned to the 2-fold axis of Rubisco is shown. b) Cryo-EM density- map of NosRcaΔC in the NosRcaΔC-Rubisco complex in cis (surface in contact with Rubisco). c) Comparison of the closed state and NosRcaΔC-engaged open state of Rubisco s sugar phosphate binding pocket. Closed state (RbcL-A, light blue; RbcL-B, dark blue); open state (RbcL-A, red; RbcL-B, peach).

PRINCIPAL PUBLICATION AND AUTHORS

Dual Functions of a Rubisco Activase in Metabolic Repair and Recruitment to Carboxysomes, M. Flecken (a), H. Wang (a), L. Popilka (a), F.U. Hartl (a), A. Bracher (a), M. Hayer-Hartl (a), Cell 183(2), 457-473 (2020); https:/doi.org/10.1016/j.cell.2020.09.010 (a) Max Planck Institute of Biochemistry, Martinsried (Germany)

REFERENCES

[1] O. Mueller-Cajar et al., Nature 479, 194-199 (2011). [2] J.Y. Bhat et al., Mol. Cell 67(5), 744-756 (2017). [3] H. Wang et al., Nature 566, 131-135 (2019).

revealed one prominent conformation of the complex, reconstruction of which resulted in a density map with an overall resolution of ~2.86 Å (Figure 36a). The NosRcaΔC is docked onto one corner of the cube-shaped Rubisco and the engaged catalytic site is in an open conformation with no discernible density for the inhibitory sugar, indicating that a post-remodelling state was captured. A key feature of the complex was the presence of well-defined density of the N-terminus of the Rubisco RbcL-A subunit in the NosRcaΔC hexamer pore (Figure 36b). Superposition of the open and closed conformations of the sugar phosphate binding site of Rubisco revealed the structural changes induced by NosRca

upon binding the N-terminal RbcL sequence (Figure 36c): first, the region following the N-terminal tail, which forms part of the roof of the active-site pocket, is destabilised, resulting in the displacement of the 60s loop of RbcL-A away from the bound inhibitory sugar. In addition, the sheer bulk of the NosRca hexamer displaces the C-terminal tail of the adjacent RbcL-B subunit, which is layered over loop 6 and pins loop 6 over the bound sugar phosphate. As a result, loop 6 is retracted from its closed position. The combined displacement of the 60s loop and loop 6 results in the opening of the active site pocket and facilitates the release of the inhibitory sugar.