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Seminar explores how bacterial division occurs

By WILLIAM BLAIR | March 12, 2020

Erin Goley, an associate professor of biological chemistry at the Hopkins School of Medicine, presented a talk entitled “How to Divide a Bacterial Cell: Cytoskeletal Control of Cell Wall Metabolism” as part of the Department of Biological Chemistry’s Tuesday Seminar Series.

Goley explained her lab’s primary research focus: “The investigation of cytoskeletal processes and cytokinesis in bacteria.”

Cytokinesis is the physical process by which the cytoplasm of one cell divides into two “daughter” cells. The accompanying division of genetic material, known as mitosis, occurs prior to cytokinesis. 

Current efforts of her lab are concentrated on understanding cytokinesis in the model bacterium, Caulobacter crescentus, and the function and regulation of a protein called FtsZ. Goley described her reason for studying FtsZ.

“FtsZ is a tubulin-like protein that acts as a scaffold for assembly of the cytokinetic machinery,” Goley said. “This scaffold is a dynamic activator of the peptidoglycan cell wall, generating constrictive forces that drive division and direct remodeling of the cell wall.”

Despite this general understanding, the molecular details of FtsZ function are largely unknown. As a result, the mechanism and regulation of bacterial growth and division remains unclear. 

Goley’s team is using a multifaceted approach, combining bacterial genetics, microscopy, biochemistry and in vitro reconstitution to obtain a comprehensive view of the mechanisms of FtsZ action.

“These studies will inform models for how proteins at the division site direct cell growth and division, and how they integrate with other cell-cycle events in time and space,” Goley said.

Recent research in Goley’s lab has focused on the use of genetic techniques to understand FtsZ regulation of peptidoglycan metabolism, specifically how changes in the connections between FtsZ proteins affect cell division. 

FtsZ proteins combine in a dynamic structure into a “Z-ring,” which recruits division machinery and directs local cell wall remodelling, leading to the activation of the peptidoglycan wall leading to cell division. The FtsZ proteins are connected to form a Z-ring by two terminal peptides: the C-terminal conserved (CTC) peptide and the C-terminal conserved linker (CTL) peptide. 

Goley observed that production of FtsZ lacking the CTL peptide is lethal, causing cells to become filamentous, form envelope bulges and lyse. Fluorescence microscopy suggests that in Z-rings without the CTL peptide, FtsZ proteins organize into large, bundled patterns which are less likely to activate the peptidoglycan wall than the small, dynamic clusters observed in normal FtsZ proteins.

“This experiment helped us understand the importance of connections between FtsZ proteins, and the disastrous results when changes disrupt connections through a CTL-dependent mechanism,” Goley said. 

Further studies of FtsZ in Goley’s lab have revealed more complex underlying processes, including the presence of a FtsZ binding protein, called FtsA. This binding protein is responsible for linking FtsZ to the peptidoglycan layer which promotes division. 

A study from January 2020 used mutants of FtsZ to show that defective CTL assembly is propagated through the interaction between CTC and FtsA, a FtsZ binding partner. Goley explained the significance of these findings.

“This suggests the process of cell wall remodeling for constriction is controlled by the interaction of conserved C-terminal domain with the membrane-anchoring protein FtsA,” Goley said.

Goley’s research has also tackled the processes involved in triggering the FtsZ protein to activate cell division. Transcription of the genes required for metabolic homeostasis and cell proliferation, including the FtsZ protein, is guided by the sigma factor σ70. A transcriptional regulator, CdnL, associates with promoter regions where σ70 localizes and stabilizes DNA during transcription.

Goley’s lab undertook another genetic study aimed at understanding how CdnL affects the activation of the FtsZ protein. 

“When we genetically modified Caulobacter crescentus cells to lack CdnL, we observed severe morphological and growth defects. This suggested that CdnL is the key player in regulating activity of the FtsZ protein, and the continuing propagation of cytokinesis.”

The overall goal of this research, however, is to address the growing crisis in antibiotic resistance. A complete molecular understanding of the mechanisms and regulation of bacterial growth and replication will inform development of new drugs that prevent bacterial division and proliferation within infected patients. 

Goley noted that FtsZ is a particularly helpful protein to study for this application.

“FtsZ is highly conserved among bacterial species so these results will be relevant to the vast majority of bacterial species, including human and animal pathogens,” she said. “Knowledge of these disruption techniques, and the creation of drugs that capitalize on these techniques, will prove an invaluable tool to the impending antibiotic crisis.” 

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