Biology subjects

Waksman, G.

Publications and source records attributed to Waksman, G..

4 recordsLinked to original sources

bioRxiv2024

Cryo-EM Structure of the relaxosome, a complex essential for bacterial mating and the spread of antibiotic resistance genes

Bacterial mating, or conjugation was discovered nearly 80 years ago as a process transferring genes from one bacterial cell (the donor) to another (the recipient). It requires three key multiprotein complexes in the donor cell: a DNA-processing machinery called the relaxosome, a double-membrane spanning type 4 secretion system (T4SS), and an extracellular appendage termed pilus. While the near-atomic resolution structures of the T4SS and pilus are known, that of the relaxosome is not1-3. Here, we describe the cryo-EM structure of the fully assembled relaxosome encoded by the paradigm F plasmid in two different states corresponding to distinct functional steps along the DNA processing reaction. By varying the structures of model DNAs we delineate conformational changes required to initiate conjugation. Mutational studies of the various protein-protein and protein-DNA interaction hubs suggest a complex highly sensitive to trigger signals, that could arise from cell-to-cell contacts with recipient cells.

microbiology↗

bioRxiv2024

Cryo-EM Structure of the R388 plasmid conjugative pilus reveals a helical polymer characterised by an unusual pilin/phospholipid binary complex

Bacterial conjugation is a process by which DNA is transferred unidirectionally from a donor cell to a recipient cell. It is the main means by which antibiotics resistance genes spread among bacterial populations. It is crucially dependent upon the elaboration of an extracellular appendage, termed "pilus", by a large double-membrane spanning secretion system termed conjugative "type IV secretion system". Here we present the structure of the conjugative pilus encoded by the R388 plasmid. We demonstrate that, as opposed to all conjugative pili produced so far for cryo-EM structure determination, that encoded by the R388 plasmid is greatly stimulated by the presence of recipient cells. Comparison of its cryo-EM structure with existing conjugative pilus structures highlights a number of important differences between the R388 pilus structure and that of its homologues, the most prominent being the highly distinctive conformation of its bound lipid.

microbiology↗

bioRxiv2024

Cryo-EM structure of a conjugative T4SS identifies a molecular switch regulating pilus biogenesis

Conjugative Type IV Secretion Systems (T4SS) mediate bacterial conjugation, a process that enables the unidirectional exchange of genetic materials between a donor and a recipient bacterial cell. Bacterial conjugation is the primary means by which antibiotic resistance genes spread among bacterial populations (Barlow, 2009; Virolle et al, 2020). Conjugative T4SSs elaborate a long extracellular filament, termed "pilus" to connect with the recipient cell. Previously, we solved the cryo-EM structure of a conjugative T4SS. In this article, based on additional data, we present a more complete T4SS cryo-EM structure than that published earlier. Novel structural features include details of the mismatch symmetry within the OMCC, the presence of a 4th VirB8 subunit in the asymmetric unit of both the Arches and the IMC, and a hydrophobic VirB5 tip in the distal end of the stalk. However, more significantly, we provide previously-undescribed structural insights into the protein VirB10 and identify a novel regulation mechanism of T4SS-mediated pilus biogenesis by this protein, that we believe is a key checkpoint for this process.

microbiology↗

bioRxiv2017

The Cryo-Electron Microscopy Structure of the Type 1 Chaperone-Usher Pilus Rod

Chaperone-usher pili are long, polymeric protein fibres displayed on the surface of many bacterial pathogens. These critical virulence factors allow bacteria to specifically attach to host cells during infection. The type 1 and P pili of uropathogenic Escherichia coli (UPEC) play important roles during UPECs colonisation of the urinary tract, mediating bacterial attachment to the bladder and kidney, respectively. Also, their biomechanical properties that allow them to reversibly uncoil in response to flow-induced forces are critical for UPECs ability to retain a foothold in the unique and hostile environment of the urinary tract. Here we provide the 4.2 [A] resolution cryo-electron microscopy (cryo-EM) structure of the type 1 pilus rod, which together with the previous structure of the P pilus rod, enables us to understand the remarkable \"spring-like\" properties of chaperone-usher pili in more detail.

molecular biology↗