ATP-binding cassette transporters are ubiquitous membrane protein complexes that move substrates across membranes. They do so using ATP-induced conformational changes in their nucleotide-binding ...domains to alter the conformation of the transport cavity formed by their transmembrane domains. In Escherichia coli, an ATP-binding cassette transporter-like complex composed of FtsE (nucleotide-binding domain) and FtsX (transmembrane domain) has long been known to be important for cytokinesis, but its role in the process has remained mysterious. Here we identify FtsEX as a regulator of cell-wall hydrolysis at the division site. Cell-wall material synthesized by the division machinery is shared initially by daughter cells and must be split by hydrolytic enzymes called "amidases" to drive daughter-cell separation. We recently showed that the amidases require activation at the cytokinetic ring by proteins with LytM domains, of which EnvC is the most critical. In this report, we demonstrate that FtsEX directly recruits EnvC to the septum via an interaction between EnvC and a periplasmic loop of FtsX. Importantly, we also show that FtsEX variants predicted to be ATPase defective still recruit EnvC to the septum but fail to promote cell separation. Our results thus suggest that amidase activation via EnvC in the periplasm is regulated by conformational changes in the FtsEX complex mediated by ATP hydrolysis in the cytoplasm. Since FtsE has been reported to interact with the tubulin-like FtsZ protein, our model provides a potential mechanism for coupling amidase activity with the contraction of the FtsZ cytoskeletal ring.
Summary
Cell division in Escherichia coli begins with the polymerization of FtsZ into a ring‐like structure, the Z‐ring, at midcell. All other division proteins are thought to require the Z‐ring for ...recruitment to the future division site. Here, it is reported that the Z‐ring associated proteins ZapA and ZapB form FtsZ‐independent structures at midcell. Upon Z‐ring disruption by the FtsZ polymerization antagonist SulA, ZapA remained at midcell as a cloud‐like accumulation. Using ZapA(N60Y), a variant defective for interaction with FtsZ, it was established that these ZapA structures form without a connection to the Z‐ring. Furthermore, midcell accumulations of GFP‐ZapA(N60Y) often preceded Z‐rings at midcell and required ZapB to assemble, suggesting that ZapB polymers form the foundation of these structures. In the absence of MatP, a DNA‐binding protein that links ZapB to the chromosomal terminus region, cloud‐like ZapA structures still formed but failed to track with the chromosome terminus and did not consistently precede FtsZ at midcell. Taken together, the results suggest that FtsZ‐independent structures of ZapA–ZapB provide additional positional cues for Z‐ring formation and may help coordinate its assembly with chromosome replication and segregation.
We found that E. coli's FtsZ‐ring associated protein ZapA forms FtsZ‐independent structures at midcell that are dependent on ZapB. Furthermore, these ZapA–ZapB structures are capable of identifying new sites of division prior to polymerization of the FtsZ‐ring and this phenomenon is largely dependent on the ter‐binding protein, MatP. Taken together, our results suggest that FtsZ‐independent structures of ZapA–ZapB provide additional positional cues for FtsZ‐ring formation and may help coordinate its assembly with chromosome replication and segregation.
Soft rot disease causes devastating losses to crop plants all over the world, with up to 90% loss in tropical climates. To better understand this economically important disease, we isolated four soft ...rot-causing
Erwinia persicina
strains from rotted vegetables. Notably,
E. persicina
has only recently been identified as a soft rot pathogen and a comprehensive genomic analysis and comparison has yet to be conducted. Here, we provide the first genomic analysis of
E. persicina
, compared to
Pectobacterium carotovorum
,
P. carotovorum
, and associated
Erwinia
plant pathogens. We found that
E. persicina
shares common genomic features with other
Erwinia
species and
P. carotovorum
, while having its own unique characteristics as well. The
E. persicina
strains examined here lack Type II and Type III secretion systems, commonly used to secrete pectolytic enzymes and evade the host immune response, respectively.
E. persicina
contains fewer putative pectolytic enzymes than
P. carotovorum
and lacks the Out cluster of the Type II secretion system while harboring a siderophore that causes a unique pink pigmentation during soft rot infections. Interestingly, a putative phenolic acid decarboxylase is present in the
E. persicina
strains and some soft rot pathogens, but absent in other
Erwinia
species, thus potentially providing an important factor for soft rot. All four
E. persicina
isolates obtained here and many other
E. persicina
genomes contain plasmids larger than 100 kbp that encode proteins likely important for adaptation to plant hosts. This research provides new insights into the possible mechanisms of soft rot disease by
E. persicina
and potential targets for diagnostic tools and control measures.
Summary
Proteins with LytM (Peptidase_M23) domains are broadly distributed in bacteria and have been implicated in a variety of important processes, including cell division and cell‐shape ...determination. Most LytM‐like proteins that have been structurally and/or biochemically characterized are metallo‐endopeptidases that cleave cross‐links in the peptidoglycan (PG) cell wall matrix. Notable exceptions are the Escherichia coli cell division proteins EnvC and NlpD. These LytM factors are not hydrolases themselves, but instead serve as activators that stimulate PG cleavage by target enzymes called amidases to promote cell separation. Here we report the structure of the LytM domain from EnvC, the first structure of a LytM factor implicated in the regulation of PG hydrolysis. As expected, the fold is highly similar to that of other LytM proteins. However, consistent with its role as a regulator, the active‐site region is degenerate and lacks a catalytic metal ion. Importantly, genetic analysis indicates that residues in and around this degenerate active site are critical for amidase activation in vivo and in vitro. Thus, in the regulatory LytM factors, the apparent substrate binding pocket conserved in active metallo‐endopeptidases has been adapted to control PG hydrolysis by another set of enzymes.
The model brown alga Ectocarpus has a haploid-diploid life cycle, involving alternation between two independent multicellular generations, the gametophyte and the sporophyte. Recent work has shown ...that alternation of generations is not determined by ploidy but is rather under genetic control, involving at least one master regulatory locus, OUROBOROS (ORO).
Using cell biology approaches combined with measurements of generation-specific transcript abundance we provide evidence that alternation of generations can also be regulated by non-cell autonomous mechanisms.
The Ectocarpus sporophyte produces a diffusible factor that causes major developmental reprogramming in gametophyte cells. Cells become resistant to reprogramming when the cell wall is synthetized, suggesting that the cell wall may play a role in locking an individual into the developmental program that has been engaged. A functional ORO gene is necessary for the induction of the developmental switch.
Our results highlight the role of the cell wall in maintaining the differentiated generation stage once the appropriate developmental program has been engaged and also indicate that ORO is a key member of the developmental pathway triggered by the sporophyte factor. Alternation between gametophyte and sporophyte generations in Ectocarpus is surprisingly labile, perhaps reflecting an adaptation to the variable seashore environment inhabited by this alga.
Two Pseudomonas strains (SR17 and SR18) were isolated from soft rot-diseased spinach leaves. Here, we report their genome sequences and characteristics.
Eleven
strains were isolated from soft rot-diseased vegetables. Here, we report their genome sequences and characteristics. Five isolates were found to be Pectobacterium versatile, while the other ...six were determined to be Pectobacterium brasiliense.
The brown algae are an interesting group of organisms from several points of view. They are the dominant organisms in many coastal ecosystems, where they often form large, underwater forests. They ...also have an unusual evolutionary history, being members of the stramenopiles, which are very distantly related to well-studied animal and green plant models. As a consequence of this history, brown algae have evolved many novel features, for example in terms of their cell biology and metabolic pathways. They are also one of only a small number of eukaryotic groups to have independently evolved complex multicellularity. Despite these interesting features, the brown algae have remained a relatively poorly studied group. This situation has started to change over the last few years, however, with the emergence of the filamentous brown alga Ectocarpus as a model system that is amenable to the genomic and genetic approaches that have proved to be so powerful in more classical model organisms such as Drosophila and Arabidopsis.
Microtubules function in concert with associated proteins that modify microtubule behavior and/or transmit signals that effect changes in growth. To better understand how microtubules and their ...associated proteins influence growth, we analyzed one family of microtubule-associated proteins, the END BINDING1 (EB1) proteins, in Arabidopsis thaliana (EB1a, EB1b, and EB1c). We find that antibodies directed against EB1 proteins colocalize with microtubules in roots, an observation that confirms previous reports using EB1-GFP fusions. We also find that T-DNA insertion mutants with reduced expression from EB1 genes have roots that deviate toward the left on vertical or inclined plates. Mutant roots also exhibit extended horizontal growth before they bend downward after tracking around an obstacle or after a 90° clockwise reorientation of the root. These observations suggest that leftward deviations in root growth may be the result of delayed responses to touch and/or gravity signals. Root lengths and widths are normal, indicating that the delay in bend formation is not due to changes in the overall rate of growth. In addition, the genotype with the most severe defects responds to low doses of microtubule inhibitors in a manner indistinguishable from the wild type, indicating that microtubule integrity is not a major contributor to the leftward deviations in mutant root growth.
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