FtsZ Polymers Tethered to the Membrane by ZipA Are Susceptible to Spatial Regulation by Min Waves

Bacterial cell division is driven by an FtsZ ring in which the FtsZ protein localizes at mid-cell and recruits other proteins, forming a divisome. In Escherichia coli, the first molecular assembly of the divisome, the proto-ring, is formed by the association of FtsZ polymers to the cytoplasmic membrane through the membrane-tethering FtsA and ZipA proteins. The MinCDE system plays a major role in the site selection of the division ring because these proteins oscillate from pole to pole in such a way that the concentration of the FtsZ-ring inhibitor, MinC, is minimal at the cell center, thus favoring FtsZ assembly in this region. We show that MinCDE drives the formation of waves of FtsZ polymers associated to bilayers by ZipA, which propagate as antiphase patterns with respect to those of Min as revealed by confocal fluorescence microscopy. The emergence of these FtsZ waves results from the displacement of FtsZ polymers from the vicinity of the membrane by MinCD, which efficiently competes with ZipA for the C-terminal region of FtsZ, a central hub for multiple interactions that are essential for division. The coupling between FtsZ polymers and Min is enhanced at higher surface densities of ZipA or in the presence of crowding agents that favor the accumulation of FtsZ polymers near the membrane. The association of FtsZ polymers to the membrane modifies the response of FtsZ to Min, and comigrating Min-FtsZ waves are observed when FtsZ is free in solution and not attached to the membrane by ZipA. Taken together, our findings show that the dynamic Min patterns modulate the spatial distribution of FtsZ polymers in controlled minimal membranes. We propose that ZipA plays an important role in mid-cell recruitment of FtsZ orchestrated by MinCDE.     

Polyamine conjugates of stigmasterol

Three new polyamine conjugates with stigmasterol [(3β,22E)-stigmasta-5,22-dien-3-ol] were synthesized and subjected to basic antimicrobial and cytotoxic tests. The conjugate derived from spermine, (3β,22E)-stigmasta-5,22-dien-3-yl 4(12-amino-4,9-diaza-dodecylamino)-4-oxobutanoate (5c), displayed considerable antimicrobial activity on Staphylococcus aureus at low concentration (50μgmL(-1)). The cytotoxic activity was tested on cells of human T-lymfoblastic leukemia (IC(50)=35.8±10.3μM (5c) and IC(50)=35.9±5.7μM (5b)) and normal human fibroblasts (IC(50)=38.0±2.8μM (5c) and IC(50)=45.5±1.9μM (5b)). Conjugate 5a displayed no activity in both tests.