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Updated: Nov 7, 2025

High-Resolution Complexome Profiling by Cryoslicing BN-MS Analysis
Published on: October 15, 2019
Complex structure reveals CcmM and CcmN form a heterotrimeric adaptor in β-carboxysome
Hui Sun1, Ning Cui1, Shu-Jing Han1
1Hefei National Laboratory for Physical Sciences at the Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, China.
Abstract:
Carboxysome is an icosahedral self-assembled microcompartment that sequesters RuBisCO and carbonic anhydrases within a selectively permeable protein shell. The scaffolding proteins, CcmM, and CcmN were proposed to act as adaptors that crosslink the enzymatic core to shell facets. However, the details of interaction pattern remain unknown. Here we obtained a stable heterotrimeric complex of CcmM γ-carbonic anhydrase domain (termed CcmMNT ) and CcmN, with a 1:2 stoichiometry, which interacts with the shell proteins CcmO and CcmL in vitro. The 2.9 Å crystal structure of this heterotrimer revealed an asymmetric bundle composed of one CcmMNT and two CcmN subunits, all of which adopt a triangular left-handed β-helical barrel structure. The central CcmN subunit packs against CcmMNT and another CcmN subunit via a wall-to-edge or wall-to-wall pattern, respectively. Together with previous findings, we propose CcmMNT -CcmN functions as an adaptor to facilitate the recruitment of shell proteins and the assembly of intact β-carboxysome.
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