Fig. 4: Structure of PhLP2A inside TRiC chamber after chamber closing.

a CryoEM structure of PhLP2A inside the closed TRiC chamber after ATP hydrolysis. (i) CryoEM imaging preparation scheme. (ii) Front and slice view of the closed PhLP2A-TRiC complex. N- and C-terminus of PhLP2A are labeled in the map. (iii) Top and slice view of the closed PhLP2A-TRiC complex. Due to the varying resolution, the PhLP2A density is shown at different thresholds according to the protein domains. Note that both of the folding chambers can be occupied by PhLP2A, as in open-state TRiC. Each subunit and domain are color-coded as in Fig. 1. b (i) Model of PhLP2A inside the closed TRiC chamber. The CTD is not modeled and the lowpass filtered electron density is shown instead. (ii) Summary of binding sites between PhLP2A and the closed TRiC chamber. Compacted NTD helices interact with the intermediate domain of CCT3/6 (colored in red) and the following TXD interacts with the apical domain of CCT5/2/4 (marked by a blue box). Note that although these domains are not resolved to the atomic level, the density map at the lower contour level shows the NTD close to CCT1/3 and the CTD close to the equatorial domains between CCT4/1. c Zoom-in view of the domain-wise interaction between PhLP2A and CCT subunits. (i) Molecular contacts between CCT 3/6 and the NTD of PhLP2A and (ii) between CCT5/2/4 and the TXD of PhLP2A. Contact areas are indicated by a yellow circle. Residues making contacts are displayed and labeled. d Electrostatic surface charge showing charge complementarity between PhLP2A and the closed folding chamber. The positively charged half hemisphere of CCT1/3/6/8 provides a binding surface for the negatively charged PhLP2A NTD. e Hydrophobic surface charge of closed folding chamber and PhLP2A. While the inner wall of the chamber is mostly hydrophilic and charged, part of the surface composed of CCT5/2/4 provides hydrophobic patches for PhLP2A TXD to bind on.