Biology subjects

Paavilainen, V.

Publications and source records attributed to Paavilainen, V..

5 recordsLinked to original sources

bioRxiv2022

Molecular view of ER membrane remodeling by the Sec61/TRAP translocon

Protein translocation across the endoplasmic reticulum (ER) membrane is an essential initial step in protein entry into the secretory pathway. The conserved Sec61 protein translocon facilitates polypeptide translocation and coordinates cotranslational polypeptide processing events. In cells, the majority of Sec61 is stably associated with a heterotetrameric membrane protein complex, the translocon associated protein complex (TRAP), yet the mechanism by which TRAP assists in polypeptide translocation or cotranslational modifications such as N-glycosylation remains unknown. Here, we demonstrate the structure of the core Sec61/TRAP complex bound to a mammalian ribosome by Cryo-EM. The interactions with ribosome anchor the Sec61/TRAP complex in a conformation that renders the ER membrane locally thinner by significantly curving its the lumenal leaflet. We propose a model for how TRAP stabilizes the ribosome exit tunnel to assist nascent polypeptide insertion through Sec61 and provides a ratcheting mechanism into the ER lumen by direct polypeptide interactions.

biochemistry↗

bioRxiv2022

Signal peptide mimicry primes Sec61 for client-selective inhibition

Preventing the biogenesis of disease-relevant proteins is an attractive therapeutic strategy, but attempts to target essential protein biogenesis factors have been hampered by excessive toxicity. Here, we describe KZR-8445, a cyclic depsipeptide that targets the Sec61 translocon and selectively disrupts secretory and membrane protein biogenesis in a signal peptide-dependent manner. KZR-8445 potently inhibits the secretion of proinflammatory cytokines in primary immune cells and is highly efficacious in a mouse model of rheumatoid arthritis. A cryo-EM structure reveals that KZR-8445 occupies the fully opened Se61 lateral gate and blocks access to the lumenal plug domain. KZR-8445 binding stabilizes the lateral gate helices in a manner that traps select signal peptides in the Sec61 channel and prevents their movement into the lipid bilayer. Our results establish a framework for the structure-guided discovery of novel therapeutics that selectively modulate Sec61-mediated protein biogenesis.

biochemistry↗

bioRxiv2022

TSignal: A transformer model for signal peptide prediction

Signal peptides are short amino acid segments present at the N-terminus of newly synthesized proteins that facilitate protein translocation into the lumen of the endoplasmic reticulum, after which they are cleaved off. Specific regions of signal peptides influence the efficiency of protein translocation, and small changes in their primary structure can abolish protein secretion altogether. The lack of conserved motifs across signal peptides, sensitivity to mutations, and variability in the length of the peptides, make signal peptide prediction a challenging task that has been extensively pursued over the years. We introduce TSignal, a deep transformer-based neural network architecture that utilizes BERT language models (LMs) and dot-product attention techniques. TSignal predicts the presence of signal peptides (SPs) and the cleavage site between the SP and the translocated mature protein. We show improved accuracy in terms of cleavage site and SP presence prediction for most of the SP types and organism groups. We further illustrate that our fully data-driven trained model identifies useful biological information on heterogeneous test sequences.

bioinformatics↗

bioRxiv2021

Snapshots of actin and tubulin folding inside the TRiC chaperonin

The integrity of a cells proteome depends on correct folding of polypeptides by chaperonins. The TCP-1 ring chaperonin (TRiC) acts as obligate folder for >10% of cytosolic proteins, including cytoskeletal proteins actin and tubulin. While its architecture and how it recognises folding substrates is emerging from structural studies, the subsequent fate of substrates inside the TRiC chamber is not defined. We trapped endogenous human TRiC with substrates (actin, tubulin) and co-chaperone (PhLP2A) at different folding stages, for structure determination by cryogenic electron microscopy. The already-folded regions of client proteins are anchored at the chamber wall, positioning unstructured regions towards the central space to achieve their folding. Substrates engage with different sections of the chamber during the folding cycle, coupled to TRiC open-and-close transitions. Furthermore, the cochaperone PhLP2A modulates folding, acting as a molecular strut between substrate and TRiC chamber. Our structural snapshots piece together an emerging atomistic model of client protein folding through TRiC.

biochemistry↗

bioRxiv2019

Carbonic anhydrase VII regulates dendritic spine morphology and density via actin filament bundling

Intracellular pH is a potent modulator of neuronal functions. By catalyzing (de)hydration of CO2, intracellular carbonic anhydrase (CAi) isoforms CAII and CAVII contribute to neuronal pH buffering and dynamics. The presence of two highly active isoforms suggests that they form spatially distinct CAi pools enabling subcellular modulation of pH. Here we show that CAVII, unlike CAII, is localized to the filamentous actin network, and its overexpression induces formation of thick actin bundles and membrane protrusions in fibroblasts. In neurons, CAVII is enriched in dendritic spines, and its over-expression causes aberrant spine morphology. We identified amino acids unique to CAVII that are required for direct actin interactions, promoting actin filament bundling and spine targeting. Lack of CAVII in neocortical neurons leads to reduced spine density and increased proportion of small spines. Thus, our work demonstrates highly distinct subcellular expression patterns of CAII and CAVII, and a novel, structural role of CAVII.

cell biology↗