Olson, Bradley , Osteryoung, Katherine .
Biochemical Analysis of Plant FtsZ1 and FtsZ2.
Chloroplast division in plants is mediated by FtsZ1 and FtsZ2, which are homologues of the bacterial cell division protein FtsZ. The bacterial FtsZ protein is thought to be the progenitor to tubulin, and is a GTP-dependent, filament-forming protein that encircles the bacterial division site. Similarly, plant FtsZ proteins encircle the mid-plastid. Plant FtsZ1 and FtsZ2 family proteins differ primarily at their C-termini with FtsZ2 proteins possessing a motif similar to those found in bacterial FtsZ that is responsible for binding to other bacterial cell division factors. In plants, this motif has been shown to bind to the chloroplast division protein ARC6, which contains a DnaJ-like domain and may be involved in FtsZ filament remodeling, but it is unclear whether Arc6 forms a stable complex with FtsZ in vivo.
In order to characterize the role of FtsZ1 and FtsZ2 in chloroplast division, we are taking several approaches. First, we are partially purifying and characterizing the composition of the native FtsZ-containing complex in pea stromal extracts. The partially purified FtsZ complex has an apparent molecular weight of approximately 220 kD. We will demonstrate that FtsZ1, FtsZ2 and ARC6 co-fractionate on sucrose density gradients and upon subsequent purification by anion exchange chromatography. Native PAGE and Western blot analysis also indicate that FtsZ1, FtsZ2 and Arc6 migrate in a stable complex, further suggesting that these proteins are in a stable complex in vivo. The molecular weight of this isolated complex likely represents unpolymerized FtsZ.
Recombinant FtsZ1 and FtsZ2 proteins both have GTPase activity. The GTPase activity of both proteins is magnesium-dependent similar to bacterial FtsZ. This result does not support a model in which FtsZ1 and FtsZ2 polymerize like alpha/beta-tubulin. In vitro polymerization and electron microscopy of FtsZ1 and FtsZ2 show that both proteins polymerize into filament-like structures, but both are required for bundled filament formation demonstrating the important relationship between FtsZ1 and FtsZ2. Taken together, our data support a model in which both FtsZ1 and FtsZ2 tightly bound to each other, presumably in the unpolymerized state, and are able to polymerize in a GTP-dependent manner. FtsZ binding proteins such as Arc6 may be important for remodeling and localizing the assembled FtsZ filaments.
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Laboratory Research Summary
1 - Michigan State University, Department of Biochemistry and Molecular Biology, 339 Plant Biology, East Lansing, MI, 48824, USA
2 - Michigan State University, Department of Plant Biology
Presentation Type: ASPB Minisymposium
Location: Continental A/Hilton
Date: Wednesday, July 11th, 2007
Time: 9:20 AM