Biology subjects

Firlar, E.

Publications and source records attributed to Firlar, E..

5 recordsLinked to original sources

bioRxiv2025

Structural basis of undecaprenyl phosphate glycosylation leading to polymyxin resistance in Gram-negative bacteria

In Gram-negative bacteria, the enzymatic modification of Lipid A with aminoarabinose (L-Ara4N) leads to resistance against polymyxin antibiotics and cationic antimicrobial peptides. ArnC, an integral membrane glycosyltransferase, attaches a formylated form of aminoarabinose to the lipid undecaprenyl phosphate, enabling its association with the bacterial inner membrane. Here, we present cryo-electron microscopy structures of ArnC from S. enterica in apo and nucleotide-bound conformations. These structures reveal a conformational transition that takes place upon binding of the partial donor substrate. Using coarse-grained and atomistic simulations, we provide insights into substrate coordination before and during catalysis, and we propose a catalytic mechanism that may operate on all similar metal-dependent polyprenyl phosphate glycosyltransferases. The reported structures provide a new target for drug design aiming to combat polymyxin resistance.

biochemistry↗

bioRxiv2023

Structural basis of archaeal FttA-dependent transcription termination

The ribonuclease FttA mediates factor-dependent transcription termination in archaea1-3. Here, we report the structure of a Thermococcus kodakarensis transcription pre-termination complex comprising FttA, Spt4, Spt5, and a transcription elongation complex (TEC). The structure shows that FttA interacts with the TEC in a manner that enables RNA to proceed directly from the TEC RNA-exit channel to the FttA catalytic center and that enables endonucleolytic cleavage of RNA by FttA, followed by 5[->]3 exonucleolytic cleavage of RNA by FttA and concomitant 5[->]3 translocation of FttA on RNA, to apply mechanical force to the TEC and trigger termination. The structure further reveals that Spt5 bridges FttA and the TEC, explaining how Spt5 stimulates FttA-dependent termination. The results reveal functional analogy between bacterial and archaeal factor-dependent termination, reveal functional homology between archaeal and eukaryotic factor-dependent termination, and reveal fundamental mechanistic similarities in factor-dependent termination in the three domains of life: bacterial, archaeal, and eukaryotic. One sentence summaryCryo-EM reveals the structure of the archaeal FttA pre-termination complex

molecular biology↗

bioRxiv2022

Structural basis of Rho-dependent transcription termination

Rho and NusG mediate factor-dependent transcription termination in Escherichia coli. Here, we report preparation of complexes functional in factor-dependent termination from RNA polymerase (RNAP), Rho, NusG, and synthetic nucleic-acid scaffolds, and we report cryo-EM structures of complexes. The structures show that functional factor-dependent pre-termination complexes contain a closed-ring Rho hexamer, have RNA threaded through the central channel of Rho, have 60 nt of RNA interacting sequence-specifically with the exterior of Rho and 6 nt of RNA interacting sequence-specifically with the central channel of Rho, have Rho oriented relative to RNAP such that ATP-hydrolysis-dependent translocation by Rho exerts mechanical force on RNAP, and have NusG bridging Rho and RNAP. The results explain five decades of research on Rho and provide a foundation for understanding Rho function. One sentence summaryCryo-EM reveals the structure of the functional Rho pre-termination complex

molecular biology↗

bioRxiv2020

High yield preparation of outer-membrane protein efflux pumps by in vitro refolding is concentration dependent

Overexpression of tripartite efflux pump systems in gram-negative bacteria are a principal component of antibiotic resistance. High-yield purification of the outer membrane component of these systems will enable biochemical and structural interrogation of their mechanisms of action and allow testing of compounds that target them. However, preparation of these proteins is typically hampered by low yields requiring laborious large-scale efforts. If refolding conditions can be found, refolding these proteins from inclusion bodies can lead to increased yields as compared to membrane isolations. Here, we develop a concentration-dependent folding protocol for refolding TolC, the outer membrane component of the antibiotic efflux pump from Escherichia coli. We show that by our method of re-folding, homotrimeric TolC remains folded in SDS-PAGE, retains binding to an endogenous ligand, and recapitulates the known crystal structure by single particle cryoEM analysis. We find that a key factor in successful re-folding is a concentration dependence of TolC oligomerization. We extended the scheme to CmeC, a homologous protein from Campylobacter jejuni, and find that concentration-dependent oligomerization is a general feature of these systems. Because outer-membrane efflux pump components are ubiquitous across gram-negative species, we anticipate that incorporating a concentration step in re-folding protocols will promote correct refolding allowing for reliable, high-yield preparation of this family of proteins.

biophysics↗

bioRxiv2020

Structural basis of transcription-translation coupling

In bacteria, transcription and translation are coupled processes, in which movement of RNA polymerase (RNAP) synthesizing mRNA is coordinated with movement of the first ribosome translating mRNA. Coupling is modulated by the transcription factors NusG--which is thought to bridge RNAP and ribosome--and NusA. Here, we report cryo-EM structures of Escherichia coli transcription-translation complexes (TTCs) containing different-length mRNA spacers between RNAP and the ribosome active-center P-site. Structures of TTCs containing short spacers show a state incompatible with NusG bridging and NusA binding (TTC-A; previously termed "expressome"). Structures of TTCs containing longer spacers reveal a new state compatible with NusG bridging and NusA binding (TTC-B) and reveal how NusG bridges and NusA binds. We propose that TTC-B mediates NusG- and NusA-dependent transcription-translation coupling. One Sentence SummaryCryo-EM defines states that mediate NusG- and NusA-dependent transcription-translation coupling in bacteria

molecular biology↗