| Author: | Mak, Chun Wing |
| Title: | Structural insights into lateral interactions between FtsZ protofilaments from Staphylococcus aureus |
| Advisors: | Wong, Kwok-yin (ABCT) |
| Degree: | Ph.D. |
| Year: | 2026 |
| Subject: | Cell division Staphylococcus aureus Protein-protein interactions Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | ix, 187 pages : color illustrations |
| Language: | English |
| Abstract: | The bacterial cell division process, which is crucial for bacterial reproduction and survival, is precisely controlled by a macromolecular protein complex or cell division machinery called “divisome”. Previous studies on E. coli and B. subtilis indicated that the divisome is a dynamic structure consisting of more than 30 proteins among which about 12 are essential cell division proteins. FtsZ is the first divisome protein that bundles into a Z-ring at the future division site, which in turn ensures proper positioning and functioning of downstream proteins. The polymeric Z-ring is not a continuous structure but instead consists of a patchy network of FtsZ filaments with lateral contacts. The FtsZ filaments treadmill circumferentially around the midcell in a GTP-dependent manner. Despite the knowledge about the physiological roles of FtsZ in cell division, the structural insights of higher-order structures through lateral interactions between FtsZ filaments remain obscure due to the resolution limit of the Z-ring in live cell imaging. In vitro, wild-type S. aureus FtsZ (SaFtsZ) with Mg²⁺ was found to form antiparallel doublet and antiparallel sheet. To determine the lateral FtsZ interactions within doublet and sheet, cryogenic electron microscopy (cryoEM) was employed. The 3.28-Å cryoEM structure of antiparallel SaFtsZ doublet revealed that lateral FtsZ interaction occurs through electrostatic interactions between Mg²⁺ and two negatively charged residues (E87 and E90) in helix H3. On the other hand, the 6.45-Å cryoEM structure of antiparallel sheet revealed that the lateral packing of two antiparallel doublets is induced by macromolecular crowding effect. To identify the physiological roles of lateral residues, the site-directed mutagenesis of E87, E90 and D91 residues were performed. The overall polymeric structures of mutants unveiled that E87 and E90 residues are essential for the formation of wild-type SaFtsZ doublet. In S. aureus cells, the lateral mutations lead to diffuse or punctate FtsZ localization, rather than the normal patterns of midcell localization. Overall, this study highlights the structure and functions of antiparallel FtsZ doublet in the Z-ring formation of S. aureus. |
| Rights: | All rights reserved |
| Access: | open access |
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