Work

Architecture and mechanism of the human p24 cargo receptor

Year: 2026

Type: article

Abstract: The p24 transmembrane emp24 domain family of cargo receptors is central to secretory trafficking, yet its molecular organization and regulatory principles have remained elusive. Here, we present cryo-EM structures of human p24 complex in three pH states, integrated with systematic functional analyses focused on glycosylphosphatidylinositol-anchored protein (GPI-AP) cargo. We identify a tightly interlocked p24α2-p24β1-p24δ1-p24γ2 heterotetramer as the minimal unit for GPI-AP engagement, resolving long-standing uncertainties regarding p24 stoichiometry and higher-order assembly. We reveal functional redundancy between p24α2 and p24α3, alongside selective incorporation of p24γ2 required for cargo binding. Systematic screening identifies two stable subassemblies: p24β1-p24δ1 and p24α2-p24β1-p24δ1, suggesting a stepwise assembly pathway. Comparative structural analysis across multiple pH states uncovers a conserved proton-sensing network centered on Coiled-coil layers 0 and +1 that drives coordinated transmembrane rearrangements, underlying pH-dependent cargo release. Our findings establish an integrated framework linking p24 architecture, isoform diversity, and pH regulation, offering a basis for understanding p24 trafficking complexity.

Source: Proceedings of the National Academy of Sciences

DOI: 10.1073/pnas.2610235123