Biology subjects

Fluman, N.

Publications and source records attributed to Fluman, N..

4 recordsLinked to original sources

bioRxiv2023

Membrane-embedded polar residues target membrane proteins for degradation by the quality control protease FtsH

Membrane proteins (MPs) navigate challenging biogenesis. Errors in this process are rigorously surveilled by cellular quality control to eliminate faulty MPs. The first critical challenge of this surveillance is the accurate recognition of misfolded proteins. However, how this recognition is achieved for MPs remains poorly defined. Here we reveal the specificity mechanism of FtsH, the major quality control protease clearing faulty MPs in Escherichia coli. Analyzing the in vivo degradation of two substrates, we show that lipid-facing polar residues direct substrates to FtsH-mediated degradation. Such polar residues are typically buried in the structural cores of folded MPs, and their exposure to the membrane may thus signify misfolding and flag proteins for degradation. Remarkably, lipid-facing polar residues are sufficient for recognition and can target even folded MPs for degradation. The recognition depends on the FtsH transmembrane domain. Thus, MP misfolding is sensed within the membrane to maintain a healthy membrane proteome.

biochemistry↗

bioRxiv2023

Membrane protein sequence features direct post-translational insertion

The proper folding of multispanning membrane proteins (MPs) hinges on the accurate insertion of their transmembrane helices (TMs) into the membrane. Predominantly, TMs are inserted during protein translation, via a conserved mechanism centered around the Sec translocon. Our study reveals that the C-terminal TMs (cTMs) of numerous MPs across various organisms bypass this cotranslational route, necessitating an alternative posttranslational insertion strategy. We demonstrate that evolution has refined the hydrophilicity and length of these proteins C-terminal tails to optimize cTM insertion. Alterations in the C-tail sequence disrupt cTM insertion in both E. coli and human, leading to protein defects, loss of function, and genetic diseases. In E. coli, we identify YidC, a member of the widespread Oxa1 family, as the insertase facilitating cTMs insertion, with C-tail mutations disrupting the productive interaction of cTMs with YidC. Thus, MP sequences are fine-tuned for effective collaboration with the cellular biogenesis machinery, ensuring proper membrane protein folding.

biochemistry↗

bioRxiv2019

Dynamic membrane topology in an unassembled membrane protein

Helical membrane proteins constitute roughly a quarter of all proteomes and perform diverse biological functions. To avoid aggregation, they undergo cotranslational membrane insertion and are typically assumed to attain stable transmembrane topologies immediately upon insertion. To what extent post-translational changes in topology are possible in-vivo and how they may affect biogenesis is incompletely understood. Here, we show that monomeric forms of Small Multidrug Resistance (SMR) proteins display topological dynamics, where the N-terminal transmembrane helix equilibrates between membrane-inserted and non-inserted states. We characterize the kinetics of the process and show how the composition of the helix regulates the topological dynamics. We further show that topological dynamics is a property of the unassembled monomeric protein, as the N-terminal helix becomes fixed in a transmembrane disposition upon dimerization. Membrane protein topology can thus remain dynamic long after cotranslational membrane insertion, and can be regulated by later assembly processes.

biochemistry↗

bioRxiv2017

Stable Membrane Topologies Of Small Dual-Topology Membrane Proteins

The topologies of -helical membrane proteins are generally thought to be determined during their cotranslational insertion into the membrane. It is typically assumed that membrane topologies remain static after this process has ended. Recent findings, however, question this static view by suggesting that some parts of, or even the whole protein, can reorient in the membrane on a biologically relevant time scale. Here, we focus on anti-parallel homo-or hetero-dimeric Small Multidrug Resistance proteins, and examine whether the individual monomers can undergo reversible topological inversion (flip-flop) in the membrane until they are trapped in a fixed orientation by dimerization. By perturbing dimerization using various means, we show that the membrane topology of a monomer is unaffected by the presence or absence of its dimerization partner. Thus, membrane-inserted monomers attain their final topologies independently of dimerization, suggesting that wholesale topological inversion is an unlikely event in vivo.

biochemistry↗