Biology subjects

Wohlever, M. L.

Publications and source records attributed to Wohlever, M. L..

8 recordsLinked to original sources

bioRxiv2025

An Msp1-Protease Chimera Captures Transient AAA+ Interactions and Unveils Ost4 Mislocalization Errors

Membrane protein homeostasis (proteostasis) is essential for maintaining the integrity of eukaryotic organelles. Msp1 is a membrane anchored AAA+ (ATPase Associated with cellular Activities) protein that maintains mitochondrial proteostasis by extracting aberrant proteins from the outer mitochondrial membrane. A comprehensive understanding of the physiological roles of Msp1 has been hindered because AAA+ proteins interact with substrates transiently and common strategies to stabilize this interaction lead to undesirable mitochondrial phenotypes. To circumvent these drawbacks, we fused catalytically active Msp1 to the inactivated protease domain of the AAA+ protease Yme1. The resulting chimera sequesters substrates in the catalytically inactive degradation chamber formed by the protease domain. We performed mass spectrometry analysis with the Msp1-protease chimera and identified the signal anchored protein Ost4 as a novel Msp1 substrate. Topology experiments show that Ost4 adopts mixed orientations when mislocalized to mitochondria and that Msp1 extracts mislocalized Ost4 regardless of orientation. Together, this work develops new tools for capturing transient interactions with AAA+ proteins, identifies new Msp1 substrates, and shows a surprising error in targeting of Ost4.

biochemistry↗

bioRxiv2025

Overcoming Fluorescence Loss in mEOS-based AAA+ Unfoldase Reporters Through Covalent Linkage

Recent work has demonstrated that the soluble photoconvertable fluorescent protein mEOS can be a reporter for AAA+ (ATPases Associated with diverse cellular Activities) unfoldase activity. Given that many AAA+ proteins process membrane proteins, we sought to adapt mEOS for use with membrane protein substrates. However, direct genetic fusion of mEOS to a membrane protein completely abolished fluorescence, severely limiting the utility of mEOS for studying AAA+ proteins. To circumvent this challenge, we separately purified mEOS and a AAA+ degron, covalently linked them via Sortase, and photoconverted the linked construct. This innovative approach preserves fluorescence and enables functional analysis, offering a broadly applicable platform for the study of membrane associated AAA+ proteins.

biochemistry↗

bioRxiv2025

A suite of pre-assembled, pET28b-based Golden Gate vectors for efficient protein engineering and expression

Expression and purification of recombinant proteins in E. coli is a bedrock technique in biochemistry and molecular biology. Expression optimization requires testing different combinations of solubility tags, affinity purification techniques, and site-specific proteases. This optimization is laborious and time consuming as these features are spread across different vector series and require different cloning strategies with varying efficiencies. Modular cloning kits based on the Golden Gate system exist, but are overly complicated for many applications, such as undergraduate research or simple screening of protein purification features. An ideal solution is for a single gene synthesis or PCR product to be compatible with a large series of pre-assembled Golden Gate vectors containing a broad array of purification features at either the N or C-terminus. To our knowledge, no such system exists. To fulfill this unmet need, we Golden Gate domesticated the pET28b vector and developed a suite of 21 vectors with different combinations of purification tags, solubility domains, visualization/labeling tags, and protease sites. We also developed a completely scarless vector series with 9 different N-terminal tags. The system is modular, allowing users to easily customize the vectors with their preferred combinations of features. To allow for easy visual screening of cloned vectors, we optimized constitutive expression of the fluorescent protein mScarlet3 in the reverse strand, resulting in a red to white color change upon successful cloning. Testing with the model protein sfGFP shows the ease of visual screening, high efficiency of cloning, and robust protein expression. These vectors provide versatile, high-throughput solutions for protein engineering and functional studies in E. coli.

biochemistry↗

bioRxiv2024

Energetic requirements and mechanistic plasticity in Msp1-mediated substrate extraction from lipid bilayers

AAA+ proteins are essential molecular motors involved in numerous cellular processes, yet their mechanism of action in extracting membrane proteins from lipid bilayers remains poorly understood. One roadblock for mechanistic studies is the inability to generate subunit specific mutations within these hexameric proteins. Using the mitochondrial AAA+ protein Msp1 as a model, we created covalently linked dimers with varying combinations of wild type and catalytically inactive E193Q mutations. The wide range of ATPase rates in these constructs allows us to probe how Msp1 uses the energy from ATP hydrolysis to perform the thermodynamically unfavorable task of removing a transmembrane helix (TMH) from a lipid bilayer. Our in vitro and in vivo assays reveal a non-linear relationship between ATP hydrolysis and membrane protein extraction, suggesting a minimum ATP hydrolysis rate is required for effective TMH extraction. While structural data often supports a sequential clockwise/2-residue step (SC/2R) mechanism for ATP hydrolysis, our biochemical evidence suggests mechanistic plasticity in how Msp1 coordinates ATP hydrolysis between subunits, potentially allowing for robustness in processing challenging substrates. This study enhances our understanding of how Msp1 coordinates ATP hydrolysis to drive mechanical work and provides foundational insights about the minimum energetic requirements for TMH extraction and the coordination of ATP hydrolysis in AAA+ proteins.

biochemistry↗

bioRxiv2024

The structural and biophysical basis of substrate binding to the hydrophobic groove in Ubiquilin Sti1 domains

Ubiquilins are molecular chaperones that play multifaceted roles in proteostasis, with point mutations in UBQLN2 leading to altered phase separation properties and Amyotrophic Lateral Sclerosis (ALS). Our mechanistic understanding of this essential process has been hindered by a lack of structural information on the Sti1 domain, which is essential for Ubiquilin chaperone activity and phase separation. Here, we present the first crystal structure of a Ubiquilin family Sti1 domain bound to a transmembrane domain (TMD) and show that ALS mutations disrupt the Sti1-TMD interaction. We then demonstrate that Ubiquilins contain multiple conserved, internal sequences that bind to the Sti1 domain, including the PXX region which is a hotspot for ALS mutations. We propose that these placeholder sequences prevent solvent exposure of the Sti1 hydrophobic groove and contribute to the multivalency that drives Ubiquilin phase separation. Together, this work provides a new paradigm for understanding how Sti1 domains modulate Ubiquilin chaperone activity and phase separation and offer insights into the molecular basis of ALS pathogenesis.

biochemistry↗

bioRxiv2024

E3 ligase recruitment by UBQLN2 protects substrates from proteasomal degradation

Ubiquilins are a family of proteins critical to cellular proteostasis that are also linked to several neurodegenerative diseases, with specific mutations in UBQLN2 causing dominant, X-linked ALS. Despite an initial characterization as proteasomal shuttle factors, Ubiquilins have paradoxically been reported to stabilize numerous substrates. The basis of this triage decision remains enigmatic. Many other fundamental aspects of Ubiquilin function are unclear at the mechanistic level, such as the physiological significance of Ubiquilin phase separation, the unique role of each Ubiquilin paralog, and the mechanistic defects of ALS mutants. To address these questions, we utilized a library of triple knockout (TKO) rescue cell lines with physiological expression of single Ubiquilin paralogs or disease mutants in an isogenic background. Our findings reveal that UBQLN2 has a unique ability to protect substrates from degradation and that substrate stabilization correlates with the recruitment of multiple E3 ligases, including SCFbxo7. We propose that E3 ligase recruitment promotes UBQLN2 phase separation, which protects substrates from proteasomal degradation. Consistent with this model, we demonstrate that ALS mutants, which were previously shown to have altered phase separation properties, also show a defect in substrate stabilization. Finally, we show that substrate stabilization appears to be a general feature of proteins that interact with the UBQLN2 Sti1 domains as amyloid precursor protein (APP) is also protected from proteasomal degradation by the formation of biomolecular condensates. This proposal unifies many existing observations in the field and presents a new paradigm for understanding Ubiquilin function in neurodegenerative disease.

biochemistry↗

bioRxiv2023

The AAA+ protein Msp1 selects substrates by recognizing a hydrophobic mismatch between the substrate transmembrane domain and the lipid bilayer

An essential aspect of protein quality control is enzymatic removal of membrane proteins from the lipid bilayer. Failures in this essential cellular process are associated with neurodegenerative diseases and cancer. Msp1 is a AAA+ (ATPases Associated with diverse cellular Activities) protein that removes mistargeted proteins from the outer mitochondrial membrane (OMM). How Msp1 selectively recognizes and extracts substrates within the complex OMM ecosystem, and the role of the lipid bilayer on these processes is unknown. Here, we describe the development of fully defined, rapid, and quantitative extraction assay that retains physiological substrate selectivity. Using this new assay, we systematically modified both substrates and the lipid environment to demonstrate that Msp1 recognizes substrates by a hydrophobic mismatch between the substrate TMD and the lipid bilayer. We further demonstrate that the rate limiting step in Msp1 activity is extraction of the TMD from the lipid bilayer. Together, these results provide foundational insights into how the lipid bilayer influences AAA+ mediated membrane protein extraction.

biochemistry↗

bioRxiv2021

Co-deletion of ATAD1 with PTEN primes cells for BIM-mediated apoptosis

PTEN is a potent tumor suppressor gene that is frequently mutated or deleted in human cancers. Such deletions often include portions of the 10q23 locus beyond the bounds of PTEN itself, in many cases resulting in the disruption of additional genes. Coincidental loss of PTEN-adjacent genes might impose vulnerabilities that could either affect patient outcome basally or be exploited therapeutically. Here we describe how the loss of ATAD1, which is adjacent to and frequently co-deleted with PTEN, predisposes cancer cells to apoptosis and correlates with improved survival in cancer patients. ATAD1 directly and specifically extracts the pro-apoptotic BIM protein from mitochondria to inactivate it. Cells lacking ATAD1 are hypersensitive to clinically used proteasome inhibitors, which increase BIM and trigger apoptosis. Thus, we demonstrate that mitochondrial protein quality control interfaces with cell death in a clinically actionable manner.

cancer biology↗