Polylysine is a Proteostasis Network-Engaging Structural Determinant

• DOI: 10.1021/acs.jproteome.8b00108
• Publication Date: 2018-04-10T19:59:32Z
• Authors: Wei-Han Lang; Giulia Calloni; R. Martin Vabulas
• Keywords: Proteasome Endopeptidase Complex; 0303 health sciences; Static Electricity; Active Transport, Cell Nucleus; Mass Spectrometry; 03 medical and health sciences; Cytosol; HEK293 Cells; Proteolysis; Proteostasis; Humans; Polylysine; Ribosomes; Chaperonin Containing TCP-1

C-terminal polylysine (PL) can be synthesized from the polyadenine tail of prematurely cleaved mRNAs or when a read-though of a stop codon happens. Due to the highly positive charge, PL stalls in the electrostatically negative ribosomal exit channel. The stalled polypeptide recruits the Ribosome-associated quality control (RQC) complex which processes and extracts the nascent chain. Dysfunction of the RQC leads to the accumulation of PL-tagged proteins, induction of a stress response, and cellular toxicity. Not much is known about the PL-specific aspect of protein quality control. Using quantitative mass spectrometry, we uncovered the post-ribosomal PL-processing machinery in human cytosol. It encompasses key cytosolic complexes of the proteostasis network, such as chaperonin TCP-1 ring complexes (TRiC) and half-capped 19S-20S proteasomes. Furthermore, we found that the nuclear transport machinery associates with PL, which suggests a novel mechanism by which faulty proteins can be compartmentalized in the cell. The enhanced nuclear import of a PL-tagged polypeptide confirmed this implication, which leads to questions regarding the biological rationale behind it.