UNMASKING SITES OF INTERACTION BETWEEN BACTERIAL DIVISION PROTEINS

Valdir Blasios Junior (USP); Alexandre Wilson Bisson Filho (USP); Theopi Alexandra Varvakis (USP); Frederico Gueiros Filho (USP)

Bacterial division is initiated through the recruitment of the protein FtsZ to the middle portion of the cell. This bacterial protein is homologous to tubulin and self-assembles into a structure known as the Z-ring. A crucial aspect of bacterial division is its spatial precision, which is assured by proteins that interact with FtsZ and regulate its polymerization. One of the best known regulators of FtsZ is the Min system, which inhibits Z ring formation in the polar regions of the cell and thus favors septum formation in the middle of the cell. The overexpression of Min proteins is known to be lethal to the cell because it impairs Z-ring formation not only at the poles but also in the mid-cell portion. We performed a genetic screen for FtsZ mutants with the capability to survive the overexpression of Min. To do so, an FtsZ mutant library was created through error prone PCR, and transformed into a modified Bacillus subtilis strain that overexpresses Min. Out of 70 000 screened transformants, 51 mutants that survived Min overexpression were found. In the FtsZ structure, we mapped thirteen amino acid substitutions: one in FtsZ´s C-terminal tail and most of the other twelve clustered in the HC3 helix region. The 13 mutants were tested for cross resistance to other well-known inhibitors that when overexpressed also impair cell division (MciZ and ZapA fused to MTS). Two of our Min resistant mutants showed cross-resistance to MciZ and Zap-MTS. This suggests that these mutants are not specific and thus unlikely to be affected in the FtsZ-MinC interaction site. Importantly, the non-specific mutations were not located in the HC3 helix. Because all the mutants affected in the HC3 helix are specific for MinC this suggests that this part of FtsZ contains the binding pocket for MinC.