Molecular interaction of the cell division protein ZapC, a regulator of the Escherichia coli FtsZ-ring assembly

Resumen

The divisome, the molecular machinery used by bacteria to effect the membrane constriction during cell division, is most often based on a cytoplasmic protein, FtsZ. FtsZ is assembled from the start of constriction as a ring (the FtsZ-ring) that is positioned at midcell during most of the septation process. However, FtsZ does not attach by itself to the cytoplasmic membrane. In the model Gram-negative Escherichia coli it needs other cell division proteins as FtsA and ZipA for attachment (Natale, et al., 2013, Rico, et al., 2013). Furthermore, as FtsZ is distributed along the bacterial length the assembly of the FtsZ-ring requires dedicated positioning mechanisms, as the Min system (de Boer, et al., 1989) and nucleoid occlusion (Woldringh, et al., 1991), both present in E. coli, to prevent assembly at sites different from the midcell. During FtsZ-ring assembly, FtsZ polymers are maintained by their lateral interactions and stabilize by a set of FtsZ associated proteins (Zap) (Huang, et al., 2013). The work presented in this thesis is focused on the study of FtsZ and its molecular interaction with the associated protein ZapC. In the Section 1, we study the in vitro assembly of FtsZ in the presence of divalent cations. The results led us to attempt the crystallization of the FtsZ protein from E. coli, as we describe in Section 2. During the crystallization process, up to 16 different FtsZ variants were constructed. FtsZ was also assayed in complex with another division proteins that interact directly with FtsZ, namely MinC (inhibitor) and ZapC (stabilizer). Section 3 describes the study of the molecular interaction between FtsZ and ZapC. In vitro data shows that the C-terminal of FtsZ may be involve in the interaction with ZapC. The resolution of the crystal structure of E. coli ZapC shows that the protein crystallized as a dimer. Further in vivo analysis shows that E. coli cells expressing zapC produces aberrant FtsZ-rings and leds to a filamentation phenotype. We have also investigated the rescue of excess ZapC by other cell division protein, FtsA and the gain-of-function FtsA*.