A research team led by UAB researcher David Reverter has discovered the molecular mechanism that describes in detail the process regulating cell division in bacteria, based on the binding of the MraZ protein to the dcw gene cluster. The research has been published in Nature Communications.
Cell division is a central process in all living organisms and requires the coordinated action of many proteins and other regulatory elements. In most bacteria this process is encoded in a gene cluster called the dcw operon, which groups all the genes that produce the proteins necessary to carry out cell division and bacterial wall formation.
These sets of genes are activated by proteins that act as transcription factors: they bind to the promoter region of the gene, the DNA sequence that indicates the point to start transcription, just before the first codon (the basic unit of gene information) that codes for the beginning of the protein sequence. One of these transcription factors is MraZ, the first gene of the dcw operon in all bacteria. When activated, the necessary proteins (encoded within the genes of the operon) are produced so that the bacteria can divide. It is, therefore, the transcription factor that controls the activity of the operon responsible for cell division in most bacteria.
A UAB research team, led by David Reverter, full professor in the Department of Biochemistry and Molecular Biology and researcher at the Institute of Biotechnology and Biomedicine of the UAB (IBB-UAB), has discovered the mechanism that describes in detail the process regulating cell division. Using structural biology techniques, such as X-ray crystallography and cryo-electron microscopy, the UAB team has discovered the molecular mechanism that describes how this MraZ transcription factor binds to the promoter of the dcw operon of the bacterium Mycoplasma genitalium, a species widely used in research because it has a very small genome.
The promoter of the dcw operon is formed by four “boxes” of six nucleotides, with repeated sequences, which regulate its transcription. By observing with cryo-electron microscopy the researchers were able to see directly, almost at an atomic scale, the specific contacts between the MraZ factor and the bases of the four repeated “boxes” of the dcw operon. In this way, they discovered that, for the binding of MraZ to the operon to occur, distortion in the structure of MraZ is necessary.
“This is a surprising observation. The MraZ protein is an octamer formed by eight identical subunits joined in the shape of a donut, but with a curvature that would never allow the union with the four ‘boxes’ of the promoter. However, to regulate cell division we see how the donut breaks and deforms in such a way that four of the subunits can join the four boxes of the promoter", David Reverter explains.
This direct observation of the interactions between MraZ and the promoter DNA regulating the initiation of cell division represents a very important advance, since previous approaches to understanding the mechanism have been based only on biochemical studies and computer modelling.
Furthermore, the regulatory mechanism discovered by UAB researchers "is universal to most bacteria, since all MraZ proteins are very similar, have the same octamer structure, and the DNA sequences of the promoters of the operons that regulate cell division are also similar", Reverter concludes.
The study, published in the journal Nature Communications, was led by David Reverter's research group from the Institute of Biotechnology and Biomedicine and the Department of Biochemistry and Molecular Biology of the UAB, in collaboration with the ALBA synchrotron and with the cryo-electron microscopy service of the Institute of Genetics and Molecular and Cellular Biology of Strasbourg, France.