The Plastid Division Protein AtMinD1 Is a Ca2+-ATPase Stimulated by AtMinE1

Abstract

Bacteria and plastids divide symmetrically through binary fission by accurately placing the division site at midpoint, a process initiated by FtsZ polymerization, which forms a Z-ring. In Escherichia coli precise Z-ring placement at midcell depends on controlled oscillatory behavior of MinD and MinE: In the presence of ATP MinD interacts with the FtsZ inhibitor MinC and migrates to the membrane where the MinD-MinC complex recruits MinE, followed by MinD-mediated ATP hydrolysis and membrane release. Although correct Z-ring placement during Arabidopsis plastid division depends on the precise localization of the bacterial homologs AtMinD1 and AtMinE1, the underlying mechanism of this process remains unknown. Here we have shown that AtMinD1 is a Ca 2؉ -dependent ATPase and through mutation analysis demonstrated the physiological importance of this activity where loss of ATP hydrolysis results in protein mislocalization within plastids. The observed mislocalization is not due to disrupted AtMinD1 dimerization, however; the active site AtMinD1(K72A) mutant is unable to interact with the topological specificity factor AtMinE1. We have shown that AtMinE1, but not E. coli MinE, stimulates AtMinD1-mediated ATP hydrolysis, but in contrast to prokaryotes stimulation occurs in the absence of membrane lipids. Although AtMinD1 appears highly evolutionarily conserved, we found that important biochemical and cell biological properties have diverged. We propose that correct intraplastidic AtMinD1 localization is dependent on AtMinE1-stimulated, Ca 2؉ -dependent AtMinD1 ATP hydrolysis, ultimately ensuring precise Z-ring placement and symmetric plastid division.Plastids are essential plant organelles vital for life on earth. They are not formed de novo but arise by binary fission from pre-existing plastids (1-3); plastid division is therefore essential for the maintenance and accumulation of plastid populations within plant cells. Many proteins involved in plastid division are derived from bacterial components conserved from the cyanobacterial origins of higher plant chloroplasts (4 -7), including FtsZ, an ancient tubulin-like protein that forms a Z-ring to which other components of the division machinery are recruited (8, 9). The Z-ring is localized to the plastid midpoint (10 -12), and correct Z-ring placement is mediated by the coordinated action of the prokaryotic-derived Min proteins. The Escherichia coli minB operon encodes MinC, MinD, and MinE, which together limit Z-ring placement to midcell (13-15): MinC is an antagonist of FtsZ polymerization (14, 15), and topological distribution of MinC is controlled by the ATPase MinD and the topological specificity factor MinE (16 -18). ATP-bound MinD recruits MinC to the membrane where the MinD-MinC complex forms a stable inhibition structure at the polar zone of the cell (19 -21). Topological specificity is conferred on this complex through interaction of MinE with membrane-bound MinD whereby MinE stimulates MinD ATPase activity, causing MinD to disassociate from the membrane and os...

CDP1, a novel component of chloroplast division site positioning system in Arabidopsis

“…Homologs of MinD and MinE were identified in the nuclear genome of Arabidopsis [26,27,46], indicating that a Min-like system is a conserved component of the plastid division machinery [9]. But in many aspects, characters of AtMinD and AtMinE are diverged from their homologs in prokaryotes [26,46,47]. Recently, it was shown that a plant-specific protein, MCD1, is required for FtsZ ring positioning [48].…”

Interdependency of formation and localisation of the Min complex controls symmetric plastid division

“…Investigation of the effects of substituting the corresponding conserved residue in AtMinE1 (D213) had no affect on the interaction between AtMinD1 and AtMinE1 (data not shown), suggesting that the specific amino acids involved in the interaction of AtMinD1 with AtMinE1 might have changed. However, mutations of highly conserved lysine residues in the walker A motifs of AtMinD1 (K72) , E. coli MinD (K16) (de Boer et al, 1989) and Neisseria gonorrhea MinD (K16) (RamirezArcos et al, 2002) result in loss of ATPase activity and, in the case of N. gonorrhea and Arabidopsis, this has also been demonstrated to be associated with disruption of the interaction between MinD and MinE (Ramirez-Arcos et al, 2002;Aldridge and Møller, 2005). The determination of the AtMinE1 binding site on AtMinD1 will be important for understanding the regulation of AtMinD1 ATPase activity.…”

“…The interaction of AtMinE1 and AtMinD1 is also required for stimulation of the ATPase activity of AtMinD1 . However, despite some functional similarities between the two systems, the absence of a MinC homologue in Arabidopsis, differences in the cation dependence of MinD on AtMinD1 ATPase activity (de Boer et al, 1991;Aldridge and Møller, 2005) and the evolution of plant-specific plastid division components (cf. all suggest that the plant Min proteins might have, in part, evolved novel functions and mechanisms.…”

A role for mechanosensitive channels in chloroplast and bacterial fission

“…3,5 How Arabidopsis MinD affects Z-ring assembly is not clear, though it has been established that its ATPase activity is stimulated by Ca 2+ and MinE. 22 Thus, the accumulation of high levels of cations in the absence of MS channels could favor the dissociation of MinD from bacterial or chloroplast membranes. Altered membrane potential has also been recently shown to disrupt the localization of a number of E. coli proteins including MinD.…”