On-way cellular roads: Tubulin-like proteins & their biological processes
Tubulin-like proteins cover a large family of GTPases that assemble into dynamic filaments. These cytomotive machines occur in eukaryotes, prokaryotes and mobile genetic elements (plasmids & phages) contributing to essential biological processes such as division, DNA segregation, cell transport, cell motility and polarity.
The growing body of genome sequencing keeps revealing more tubulin-like proteins and structural studies are very helpful in defining the protein family fold. So far, these GTPases can be classified into 4 sub-groups that mainly differ at the C-terminus and the relative position of N- and C-terminal domain: Tubulin, FtsZ, CetZ and TubZ
Stable inheritance of the genetic information
Partition systems are survival kits encoded in plasmids and bacteria chromosomes that allow to reliably segregating sisters DNAs. The main compact module includes: a cis-acting centromere-like DNA, a centromere binding protein (CBP) and, a motor protein (NTPase). According to the nature of the NTPase there are: type I (Walker-A ATPase), type II (actin-like ATPase) and type III (tubulin-like GTPase) partition systems.
In type III partition systems the motor protein (TubZ), works with the CBP (TubR), the centromere (tubC) and a new extra transcriptional regulator protein that we have discovered and named TubY.
We have firstly identified a type III partition system encoded in phage c-st. This is a Clostridium botulinum bacteriophage that also includes type C botulinum neurotoxin encoded in its genome. During the lysogenic stage the phage DNA is not integrated into the bacteria chromosome but stays at the cytoplasm as a plasmid entity. We think the type III partition system helps phage DNA maintenance during this stage when the bacterium divides.
We apply an integrative biology approach to this segregation machine to understand how it works. With the combination of structural studies (X-ray crystallography, Electron Microscopy and NMR) and other biophysical and biochemical tools:
- We have deciphered the molecular mechanism driving TubZ movement during DNA segregation attending to the conformational changes within the filaments that promote the disassembly.
- We are studying how TubR interacts with the DNA to form the so-called segrosome, how this macromolecular complex regulates the transcription of the operon and at the same time interacts with TubZ filaments to move the DNA to a new position in the cell.
- We are analysing the implication of the newly discovered protein TubY on the system regulation. Recent results point to a MAP-like protein, able to interact with TubZ filaments inducing disassembly into tubulin-like ring structures.