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<StructureSection load='2vam' size='340' side='right' caption='FtsZ of Bacillus subtilis' scene=''>
<StructureSection load='2vam' size='340' side='right' caption='FtsZ of Bacillus subtilis' scene=''>
== Bacillus subtilis division protein ==
== Bacillus subtilis division protein ==
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Bacillus subtilis is a prokaryotic organism, is a Gram-positive bacterium, and thus has a cytoplasmic membrane plus a thick cell wall made of peptidoglycan and associated anionic polymers, such as teicoic acid. Bacteria are recognized for the reproductive success and conquest of various environments on Earth, with the presence of a complex and sophisticated machinery of cell division and formation of identical daughter cells a potent factor in this success. There are currently 24 proteins known to be associated with division in B. subtilis: ClpX, DivIB,DivIC, DivIVA, EzrA, FtsA, FtsL, FtsW, FtsZ,GpsB, MciZ, MinC, MinD, MinJ, Noc, PBP1,PBP2B, SepF, SftA, SpoIIE, SpoIIIE, UgtP, YneA and ZapA. These can be divided in two main groups: proteins that make up the divisome and are directly involved in the construction of the septum or divisome (DivIB, DivIC, EzrA, FtsA, FtsL, FtsW,FtsZ, GpsB, PBP1, PBP2B, SepF and ZapA) and proteins that regulate the assembly of the divisome (ClpX, DivIVA, MciZ, MinC, MinD, MinJ,Noc, UgtP and YneA). Among these, the FtsZ stands out for acting in the recruitment of other proteins for the formation of the constriction ring that culminates in cell division.
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Bacillus subtilis is a prokaryotic organism, a Gram-positive bacterium, and thus has a cytoplasmic membrane plus a thick cell wall made of peptidoglycan and associated anionic polymers, such as teicoic acid. Bacteria are recognized for the reproductive success and conquest of various environments on Earth, with the presence of a complex and sophisticated machinery of cell division and formation of identical daughter cells a potent factor in this success. There are currently 24 proteins known to be associated with division in B. subtilis: ClpX, DivIB,DivIC, DivIVA, EzrA, FtsA, FtsL, FtsW, FtsZ,GpsB, MciZ, MinC, MinD, MinJ, Noc, PBP1,PBP2B, SepF, SftA, SpoIIE, SpoIIIE, UgtP, YneA and ZapA. These proteins can be divided in two main groups: proteins that make up the divisome - macromolecular complex composed of about 20 proteins, which promotes the construction of the cell wall and cytoplasmic membrane, forming the division septum (DivIB, DivIC, EzrA, FtsA, FtsL, FtsW,FtsZ, GpsB, PBP1, PBP2B, SepF and ZapA) and proteins that regulate the assembly of the divisome (ClpX, DivIVA, MciZ, MinC, MinD, MinJ,Noc, UgtP and YneA). Among these, the FtsZ stands out for acting in the recruitment of other proteins for the formation of the constriction ring that culminates in cell division.
== Function ==
== Function ==
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FtsZ (Filamentation temperature sensitive Z) is the master coordinator of septum formation and the most widely conserved division protein, being present in essentially all bacterial genomes that have been sequenced to date. This protein is extremely important to binary fission - more specifically, formation of the Z ring - in rod-shaped bacteria entails the formation of a transverse septum that divides a progenitor cell into two equal-sized daughter cells. Septum formation is faithfully coordinated with chromosome replication and segregation and the spatial control, on the other hand, is evident in the placement of the newly formed septum at precisely the middle of the progenitor cell, which ensures that the two daughter cells generated are morphologically and genetically equivalent. It means that despite the apparent simplicity, cell division in bacteria is subject to tight spatiotemporal control.
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FtsZ (Filamentation temperature sensitive Z) is the main coordinator of septum formation and the most widely conserved division protein, being present in essentially all bacterial genomes that have been sequenced to date. In eubacteria, the FtsZ gene is usually found in the dcw gene cluster, a DNA region containing division and cell-wall synthesis gene. This protein is extremely important to binary fission - more specifically, formation of the Z ring - in rod-shaped bacteria entails the formation of a transverse septum that divides a progenitor cell into two equal-sized daughter cells. Septum formation is faithfully coordinated with chromosome replication and segregation and the spatial control, on the other hand, is evident in the placement of the newly formed septum at precisely the middle of the progenitor cell, which ensures that the two daughter cells generated are morphologically and genetically equivalent. It means that despite the apparent simplicity, cell division in bacteria is subject to tight spatiotemporal control.
== Structural highlights ==
== Structural highlights ==
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== Polymerization mechanism ==
== Polymerization mechanism ==
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In order for polymerization of the monomers of FtsZ to occur, there is a need for interaction of the N-terminal nucleotide binding domain with the C-terminal domain of another monomer. The formation of a complete GTP hydrolysis site depends on the positioning of acid residues of the T7 loop at the nucleotide binding site of the prior monomer in the polymer, explaining why the GTPase activity of FtsZ only occurs when the protein is in the polymer form. The binding of GTP promotes the longitudinal association of the monomers forming protofilaments, and the hydrolysis of the nucleotide leads to depolymerization and consequent disorganization of the protofilament. However, there is still controversy regarding the mechanism of polymerization of FtsZ and details of the process are being elucidated. What is currently in place is that loop motion between the H6-H7 helices away from the nucleotide cavity (downward movement of the H7 helix, and 23-degree rotation of the C-terminal domain relative to the N-terminus), creates a groove between the C-terminal domain and the H7 helix that does not exist in the structures described above. This conformation promotes the insertion of the T7 loop in the active site of another monomer, which in the presence of divalent cation would stabilize a dimeric interface with more extensive contacts leading to polymerization. Therefore, the "assembly switch" would be the conversion of a monomer into the closed conformation (without the groove between H7 and C-terminus) to the open conformation (with the groove between H7 and the C-terminus), the latter competent for polymerization.
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In order for polymerization of the monomers of FtsZ to occur, there is a need for interaction of the N-terminal nucleotide binding domain with the C-terminal domain of another monomer. The formation of a complete GTP hydrolysis site depends on the positioning of acid residues of the T7 loop at the nucleotide binding site of the prior monomer in the polymer, explaining why the GTPase activity of FtsZ only occurs when the protein is in the polymer form. The fact that FtsZ GTPase activity interferes with the dynamics of its autoassociation and the morphology of its polymers, as well as with microtubules and actin, opens the possibility that FtsZ can also present dynamic treadmilling or instability.
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The binding of GTP promotes the longitudinal association of the monomers forming protofilaments, and the hydrolysis of the nucleotide leads to depolymerization and consequent disorganization of the protofilament. FtsZ protofilaments have a strong tendency to associate further to form multi-stranded polymers. The tendency of FtsZ filaments to form lateral interactions in greatly increased by the presence of cations such the Ca2+.
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However, there is still controversy regarding the mechanism of polymerization of FtsZ and details of the process are being elucidated. What is currently in place is that loop motion between the H6-H7 helices away from the nucleotide cavity (downward movement of the H7 helix, and 23-degree rotation of the C-terminal domain relative to the N-terminal), creates a groove between the C-terminal domain and the H7 helix that does not exist in the structures described above. This conformation promotes the insertion of the T7 loop in the active site of another monomer, which in the presence of divalent cation would stabilize a dimeric interface with more extensive contacts leading to polymerization. Therefore, the "assembly switch" would be the conversion of a monomer into the closed conformation (without the groove between H7 and C-terminal) to the open conformation (with the groove between H7 and the C-terminus), the latter competent for polymerization.
== Relevance ==
== Relevance ==

Revision as of 14:26, 12 June 2019

FtsZ of Bacillus subtilis

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Jonathan Cardoso C. Vieira

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