Identification of the coiled-coil domains of Enterococcus faecalis DivIVA that mediate oligomerization and their importance for biological function

The roles of GpsB and DivIVA in Staphylococcus aureus growth and division

The spheroid bacterium Staphylococcus aureus is often used as a model of morphogenesis due to its apparently simple cell cycle. S. aureus has many cell division proteins that are conserved across bacteria alluding to common functions. However, despite intensive study, we still do not know the roles of many of these components. Here, we have examined the functions of the paralogues DivIVA and GpsB in the S. aureus cell cycle. Cells lacking gpsB display a more spherical phenotype than the wild-type cells, which is associated with a decrease in peripheral cell wall peptidoglycan synthesis. This correlates with increased localization of penicillin-binding proteins at the developing septum, notably PBPs 2 and 3. Our results highlight the role of GpsB as an apparent regulator of cell morphogenesis in S. aureus.

CcpN: a moonlighting protein regulating catabolite repression of gluconeogenic genes in Bacillus subtilis also affects cell length and interacts with DivIVA

CcpN is a transcriptional repressor in Bacillus subtilis that binds to the promoter region of gapB and pckA, downregulating their expression in the presence of glucose. CcpN also represses sr1, which encodes a small noncoding regulatory RNA that suppresses the arginine biosynthesis gene cluster. CcpN has homologues in other Gram-positive bacteria, including Enterococcus faecalis. We report the interaction of CcpN with DivIVA of B. subtilis as determined using bacterial two-hybrid and glutathione S-transferase pull-down assays. Insertional inactivation of CcpN leads to cell elongation and formation of straight chains of cells. These findings suggest that CcpN is a moonlighting protein involved in both gluconeogenesis and cell elongation.

Age-dependent root canal instrumentation techniques: a comprehensive narrative review

The aim of this article was to review age-dependent clinical recommendations for appropriate root canal instrumentation techniques. A comprehensive narrative review of canal morphology, the structural characteristics of dentin, and endodontic outcomes at different ages was undertaken instead of a systematic review. An electronic literature search was carried out, including the Medline (Ovid), PubMed, and Web of Science databases. The searches used controlled vocabulary and free-text terms, as follows: 'age-related root canal treatment,' 'age-related instrumentation,' 'age-related chemo-mechanical preparation,' 'age-related endodontic clinical recommendations,' 'root canal instrumentation at different ages,' 'geriatric root canal treatment,' and 'pediatric root canal treatment.' Due to the lack of literature with practical age-based clinical recommendations for an appropriate root canal instrumentation technique, a narrative review was conducted to suggest a clinical algorithm for choosing the most appropriate instrumentation technique during root canal treatment. Based on the evidence found through the narrative review, an age-related clinical algorithm for choosing appropriate instrumentation during root canal treatment was proposed. Age affects the morphology of the root canal system and the structural characteristics of dentin. The clinician's awareness of root canal morphology and dentin characteristics can influence the choice of instruments for root canal treatment.

EF1025, a Hypothetical Protein From Enterococcus faecalis, Interacts With DivIVA and Affects Cell Length and Cell Shape

DivIVA plays multifaceted roles in Gram-positive organisms through its association with various cell division and non-cell division proteins. We report a novel DivIVA interacting protein in Enterococcus faecalis, named EF1025 (encoded by EF1025), which is conserved in Gram-positive bacteria. The interaction of EF1025 with DivIVA_Ef was confirmed by Bacterial Two-Hybrid, Glutathione S-Transferase pull-down, and co-immunoprecipitation assays. EF1025, which contains a DNA binding domain and two Cystathionine β-Synthase (CBS) domains, forms a decamer mediated by the two CBS domains. Viable cells were recovered after insertional inactivation or deletion of EF1025 only through complementation of EF1025 in trans. These cells were longer than the average length of E. faecalis cells and had distorted shapes. Overexpression of EF1025 also resulted in cell elongation. Immuno-staining revealed comparable localization patterns of EF1025 and DivIVA_Ef in the later stages of division in E. faecalis cells. In summary, EF1025 is a novel DivIVA interacting protein influencing cell length and morphology in E. faecalis.

Structural basis for interaction of DivIVA/GpsB proteins with their ligands

DivIVA proteins and their GpsB homologues are late cell division proteins found in Gram-positive bacteria. DivIVA/GpsB proteins associate with the inner leaflet of the cytosolic membrane and act as scaffolds for other proteins required for cell growth and division. DivIVA/GpsB proteins comprise an N-terminal lipid-binding domain for membrane association fused to C-terminal domains supporting oligomerization. Despite sharing the same domain organization, DivIVA and GpsB serve different cellular functions: DivIVA plays diverse roles in division site selection, chromosome segregation and controlling peptidoglycan homeostasis, whereas GpsB contributes to the spatiotemporal control of penicillin-binding protein activity. The crystal structures of the lipid-binding domains of DivIVA from Bacillus subtilis and GpsB from several species share a fold unique to this group of proteins, whereas the C-terminal domains of DivIVA and GpsB are radically different. A number of pivotal features identified from the crystal structures explain the functional differences between the proteins. Herein we discuss these structural and functional relationships and recent advances in our understanding of how DivIVA/GpsB proteins bind and recruit their interaction partners, knowledge that might be useful for future structure-based DivIVA/GpsB inhibitor design.

Role of cell division protein divIVA in Enterococcus faecalis pathogenesis, biofilm and drug resistance: A future perspective by in silico approaches

Antibiotics resistance is the major problem in clinical settings which leads to the emergence of drug resistant bacteria. Biofilm formation is one of the grounds for the emergence of antibiotics resistant strains of Enterococcus faecalis. Our group previously reported in a comparative proteomic study of biofilm and planktonic state of E. faecalis that cell division protein divIVA was two folds overexpressed in biofilm state as compared to planktonic one and suggested its involvement in biofilm formation and antibiotics resistance. In this in silico study molecular docking showed that DNA bind to the conserved amino acid residues of divIVA domain and suggested that divIVA possibly secretes DNA into extra polymeric substance (EPS) which is the part of biofilm. We also performed the STRING analysis of cell division protein divIVA and predicted their interactive partners {cell division proteins/divisome complex (ftsZ, ftsA, divIV, ftsL, & gpsB), hypothetical proteins (sepF, EF_0261, EF_1000, EF_0998, EF_1006 & EF_1040), isoleucyl-tRNA synthetase (ileS), septation ring formation regulator (ezrA), S4 domain-containing protein (EF_1001), rod shape-determining protein (mreC), UDP-N-acetylmuramoyl-L-alanyl-d-glutamate synthetase (murD), UDP-diphospho-muramoyl-pentapeptide beta-N- acetylglucosaminyltransferase (murG), Lipoprotein signal peptidase (lspA), adenylate kinase (adk) and DNA-binding response regulator (vicR)}. We suggest that cumulatively divIVA and its interactive partners might be directly or indirectly involved in E. faecalis cell division, growth, biofilm formation, virulence and resistance.

Minor Type IV Collagen α5 Chain Promotes Cancer Progression through Discoidin Domain Receptor-1

Type IV collagens (Col IV), components of basement membrane, are essential in the maintenance of tissue integrity and proper function. Alteration of Col IV is related to developmental defects and diseases, including cancer. Col IV α chains form α1α1α2, α3α4α5 and α5α5α6 protomers that further form collagen networks. Despite knowledge on the functions of major Col IV (α1α1α2), little is known whether minor Col IV (α3α4α5 and α5α5α6) plays a role in cancer. It also remains to be elucidated whether major and minor Col IV are functionally redundant. We show that minor Col IV α5 chain is indispensable in cancer development by using α5(IV)-deficient mouse model. Ablation of α5(IV) significantly impeded the development of Kras^G12D-driven lung cancer without affecting major Col IV expression. Epithelial α5(IV) supports cancer cell proliferation, while endothelial α5(IV) is essential for efficient tumor angiogenesis. α5(IV), but not α1(IV), ablation impaired expression of non-integrin collagen receptor discoidin domain receptor-1 (DDR1) and downstream ERK activation in lung cancer cells and endothelial cells. Knockdown of DDR1 in lung cancer cells and endothelial cells phenocopied the cells deficient of α5(IV). Constitutively active DDR1 or MEK1 rescued the defects of α5(IV)-ablated cells. Thus, minor Col IV α5(IV) chain supports lung cancer progression via DDR1-mediated cancer cell autonomous and non-autonomous mechanisms. Minor Col IV can not be functionally compensated by abundant major Col IV.

Collagens, the major extracellular matrix components in most vertebrate tissues, provide cells with structural and functional support. Collagens are trimers of collagen α chains. Multiple trimers are formed by highly homologous α chains for certain types of collagens (e.g. α1α1α2, α3α4α5 and α5α5α6 heterotrimers for type IV collagen). Type IV collagens are named as major type (α1α1α2) or minor type (α3α4α5 and α5α5α6), mainly reflecting the abundance and tissue distribution, but not the importance of their biological functions. High similarity in sequence and domain structure of the α chains does not necessarily imply that major and minor type IV collagens share the same cell surface receptors and intracellular signaling pathways. In this study, we generated an α5(IV) chain deficient mouse model lacking minor type IV collagens. We found that the mutant mice have delayed development of Kras^G12D-driven lung cancer without affecting major type IV collagen expression. α5(IV), but not α1(IV), ablation impaired non-integrin collagen receptor discoidin domain receptor-1 (DDR1)-ERK signaling, suggesting that major and minor type IV collagens are functionally distinct from each other.

SecA is required for membrane targeting of the cell division protein DivIVA in vivo

The conserved protein DivIVA is involved in different morphogenetic processes in Gram-positive bacteria. In Bacillus subtilis, the protein localizes to the cell division site and cell poles, and functions as a scaffold for proteins that regulate division site selection, and for proteins that are required for sporulation. To identify other proteins that bind to DivIVA, we performed an in vivo cross-linking experiment. A possible candidate that emerged was the secretion motor ATPase SecA. SecA mutants have been described that inhibit sporulation, and since DivIVA is necessary for sporulation, we examined the localization of DivIVA in these mutants. Surprisingly, DivIVA was delocalized, suggesting that SecA is required for DivIVA targeting. To further corroborate this, we performed SecA depletion and inhibition experiments, which provided further indications that DivIVA localization depends on SecA. Cell fractionation experiments showed that SecA is important for binding of DivIVA to the cell membrane. This was unexpected since DivIVA does not contain a signal sequence, and is able to bind to artificial lipid membranes in vitro without support of other proteins. SecA is required for protein secretion and membrane insertion, and therefore its role in DivIVA localization is likely indirect. Possible alternative roles of SecA in DivIVA folding and/or targeting are discussed.

RNase Y in Bacillus subtilis: a Natively disordered protein that is the functional equivalent of RNase E from Escherichia coli

The control of mRNA stability is an important component of regulation in bacteria. Processing and degradation of mRNAs are initiated by an endonucleolytic attack, and the cleavage products are processively degraded by exoribonucleases. In many bacteria, these RNases, as well as RNA helicases and other proteins, are organized in a protein complex called the RNA degradosome. In Escherichia coli, the RNA degradosome is assembled around the essential endoribonuclease E. In Bacillus subtilis, the recently discovered essential endoribonuclease RNase Y is involved in the initiation of RNA degradation. Moreover, RNase Y interacts with other RNases, the RNA helicase CshA, and the glycolytic enzymes enolase and phosphofructokinase in a degradosome-like complex. In this work, we have studied the domain organization of RNase Y and the contribution of the domains to protein-protein interactions. We provide evidence for the physical interaction between RNase Y and the degradosome partners in vivo. We present experimental and bioinformatic data which indicate that the RNase Y contains significant regions of intrinsic disorder and discuss the possible functional implications of this finding. The localization of RNase Y in the membrane is essential both for the viability of B. subtilis and for all interactions that involve RNase Y. The results presented in this study provide novel evidence for the idea that RNase Y is the functional equivalent of RNase E, even though the two enzymes do not share any sequence similarity.

Transduction of the Hedgehog signal through the dimerization of Fused and the nuclear translocation of Cubitus interruptus

The Hedgehog (Hh) family of secreted proteins is essential for development in both vertebrates and invertebrates. As one of main morphogens during metazoan development, the graded Hh signal is transduced across the plasma membrane by Smoothened (Smo) through the differential phosphorylation of its cytoplasmic tail, leading to pathway activation and the differential expression of target genes. However, how Smo transduces the graded Hh signal via the Costal2 (Cos2)/Fused (Fu) complex remains poorly understood. Here we present a model of the cell response to a Hh gradient by translating Smo phosphorylation information to Fu dimerization and Cubitus interruptus (Ci) nuclear localization information. Our findings suggest that the phosphorylated C-terminus of Smo recruits the Cos2/Fu complex to the membrane through the interaction between Smo and Cos2, which further induces Fu dimerization. Dimerized Fu is phosphorylated and transduces the Hh signal by phosphorylating Cos2 and Suppressor of Fu (Su(fu)). We further show that this process promotes the dissociation of the full-length Ci (Ci155) and Cos2 or Su(fu), and results in the translocation of Ci155 into the nucleus, activating the expression of target genes.

Domains involved in the in vivo function and oligomerization of apical growth determinant DivIVA in Streptomyces coelicolor

The coiled-coil protein DivIVA is a determinant of apical growth and hyphal branching in Streptomyces coelicolor. We have investigated the properties of this protein and the involvement of different domains in its essential function and subcellular targeting. In S. coelicolor cell extracts, DivIVA was present as large oligomeric complexes that were not strongly membrane associated. The purified protein could self-assemble into extensive protein filaments in vitro. Two large and conspicuous segments in the amino acid sequence of streptomycete DivIVAs not present in other homologs, an internal PQG-rich segment and a carboxy-terminal extension, are shown to be dispensable for the essential function in S. coelicolor. Instead, the highly conserved amino-terminal of 22 amino acids was required and affected establishment of new DivIVA foci and hyphal branches, and an essential coiled-coil domain affected oligomerization of the protein.

Localisation of DivIVA by targeting to negatively curved membranes

DivIVA is a conserved protein in Gram-positive bacteria and involved in various processes related to cell growth, cell division and spore formation. DivIVA is specifically targeted to cell division sites and cell poles. In Bacillus subtilis, DivIVA helps to localise other proteins, such as the conserved cell division inhibitor proteins, MinC/MinD, and the chromosome segregation protein, RacA. Little is known about the mechanism that localises DivIVA. Here we show that DivIVA binds to liposomes, and that the N terminus harbours the membrane targeting sequence. The purified protein can stimulate binding of RacA to membranes. In mutants with aberrant cell shapes, DivIVA accumulates where the cell membrane is most strongly curved. On the basis of electron microscopic studies and other data, we propose that this is due to molecular bridging of the curvature by DivIVA multimers. This model may explain why DivIVA localises at cell division sites. A Monte-Carlo simulation study showed that molecular bridging can be a general mechanism for binding of proteins to negatively curved membranes.

Assemblies of DivIVA mark sites for hyphal branching and can establish new zones of cell wall growth in Streptomyces coelicolor

Time-lapse imaging of Streptomyces hyphae revealed foci of the essential protein DivIVA at sites where lateral branches will emerge. Overexpression experiments showed that DivIVA foci can trigger establishment of new zones of cell wall assembly, suggesting a key role of DivIVA in directing peptidoglycan synthesis and cell shape in Streptomyces.