Tubulin are the proteins specific to eukaryotic cells, however, prokaryotes—bacteria—also have a protein named FtsZ, which is homologous to tubulin. FtsZ protein are crucial for bacterial cell division process as they help bacteria to segregate daughter cells by forming a Z-ring at the center of dividing cell which after cell division, results into a septum between two progeny bacteria. Due to this mechanical property of FtsZ protein, it is known by bacterial cytoskeletal protein (1). FtsZ proteins are rapidly assembled at the time of cell division in a bacterial cell. Although there exist several factors within the cell that significantly inhibit the FtsZ assembly, “Nucleoid Occlusion (NO)” and “Min system” approaches of negative regulation are highly studied. Widely known regulator proteins involved in NO approach are SlmA and Noc. These proteins bind to specific sequence of bacterial DNA known as Noc Binding Site (NBS) and SlmA Binding Site (SBS) respectively for Noc and SlmA, forming a NO at the center of cell. For example, when SlmA binds to SBS of DNA, the interaction attracts polymerized FtsZ molecule at the center of cell eventually destabilizing the newly polymerized Z-ring, resulting into dissociation of the ring into monomers (2). Once the Z-ring is disassembled, the cell cannot be segregated into two cells as the mechanical force for the segregation of cellular organelles is lacking. This mechanism eventually prevents bacteria from dividing into two separate cells. It is known that Noc and SlmA bind to DNA and form NO in similar fashion, however, the exact mechanism of FtsZ inhibition by Noc protein is not known. Noc protein are found specifically in Bacillus subtilis where as SlmA are found in several different types of bacteria, such as Eschericia coli, Vibrio cholerae, and Klebsiella pneumonae. FtsZ regulation by Min system involves a set of different proteins namely, MinC, MinD and MinE in Escherichia coli. Among these proteins, MinC is involved in inhibition of FtsZ if it is improperly placed within the cell. The Min System therefore plays significant role in maintaining equal size of daughter cells.
Schumacher MZeng W. 2016. Structures of the nucleoid occlusion protein SlmA bound to DNA and the C-terminal domain of the cytoskeletal protein FtsZ. Proceedings of the National Academy of Sciences 113:4988-4993.
This article gives a review on SlmA protein and how does this protein bind to DNA of bacteria to form NO and gives the light on how does it eventually dismantle FtsZ ring into protofilament monomers rendering it ineffective. That article starts with the description of SlmA protein and mechanisms how it binds to DNA. This article also mentions other protein that work similar to SlmA. According to this article, SlmA protein binds to DNA as a dimer of dimer and spreads along the DNA and finds to C-terminal domain (CTD) of FtsZ. It is stated that SlmA becomes active only after it binds to DNA and CTD of FtsZ. The structural similarity between SlmA-DNA-CTD of Ftsz interaction in Escherichia coli, Vibrio cholera, and two strains of Klebsiella pneumonia are stated in a result section. Although it was believed that all SlmA proteins bind to 5′-GTGAGTACTCAC-3′ on SBS but this article has refuted this fact. The article states that the sequence of SBS varies depending upon the strains of organism. They also found that there is no conformational changes at the SlmA-CTD complex in all three species of bacteria. They have found this result by crystallization of complexes of SlmA–DNA with the CTD of FtsZ. The article states efficient interactions are possible only when the SlmA binds to specific DNA sequences. To verify this, the authors found different DNA binding domains and multiple structure of apo SlmA in different species of bacteria. This article finds the hydrophobic region between SBS and C-domain of FtsZ CTD binding site of SlmA.
The interaction between FtsZ CTD, SlmA is clearly illustrated. Introduction is straight forward. The authors have mentioned the structure and sequence of SBS, which is informative. The article has lucid methodology section even though it was separated from the main article and kept at supplementary section. It is very convincing that crystallization of SlmA-CTD of FtsZ complex provides a fair idea of the molecular structure. The use two different approaches for crystallization of SmlA-CDT of FtsZ complex and DNA-SmlA-CDT of FtsZ complex is logical. Although some crystallographic images were clearly articulated, results are vaguely presented. In some places, it is hardly understandable. The SlmA-DNA interaction is clearly discussed but no clue of similar protein has been given in discussion. In addition, the molecular mechanism by which FtsZ is inhibited is not clearly stated. The cartoons for visual illustration provided in article was insufficient.
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