Segrosome

Overview
Segrosomes are protein complexes that ensure accurate segregation (partitioning) of plasmids or chromosomes during bacterial cell division.

Just as higher forms of life have evolved a complex mitotic apparatus to partition duplicated DNA during cell division, bacteria require a specialized apparatus to partition their duplicated DNA. In bacteria, segrosomes perform the function similar to that performed by mitotic spindle. Therefore, segrosomes can be thought of as minimalist spindles.

Segrosomes are usually composed of three basic components- the DNA (plasmid or chromosome) that needs to be segregated into daughter cells, a motor protein that provides the necessary physical forces for accomplishing the segregation and a DNA binding protein that connects the DNA and the motor protein, to form the complete segrosome complex.

Motor proteins present in bacterial segrosomal complexes
The majority of motor proteins participating in plasmid segrosomes is comprised of Walker-type or ParM type ATPases. Segrosome formation could be a highly regulated and ordered process to ensure its coupling with the other events of the bacterial cell cycle. Recently segrosomal complexes derived from the tubulin family of cytoskeletal proteins, which are GTPases have been discovered in megaplasmids found in Bacillus species.

Additional Resources

 * 1) Hayes F, Barillà D. The bacterial segrosome: a dynamic nucleoprotein machine for DNA trafficking and segregation.Nat Rev Microbiol. 2006 Feb;4(2):133-43.
 * 2) Hayes F, Barillà D. Assembling the bacterial segrosome. Trends Biochem Sci. 2006 May;31(5):247-50. Epub 2006 Apr 11.
 * 3) Tinsley E, Khan SA. A novel FtsZ-like protein is involved in replication of the anthrax toxin-encoding pXO1 plasmid in Bacillus anthracis. J Bacteriol. 2006 Apr;188(8):2829-35.
 * 4) Larsen RA, Cusumano C, Fujioka A, Lim-Fong G, Patterson P, Pogliano J.Treadmilling of a prokaryotic tubulin-like protein, TubZ, required for plasmid stability in Bacillus thuringiensis. Genes Dev. 2007 Jun 1;21(11):1340-52. Epub 2007 May 17.
 * 5) Margolin, W. Bacterial cytoskeleton: not your run-of-the-mill tubulin. Curr Biol. 2007 Aug 21;17(16):R633-
 * 6) Anand SP, Akhtar P, Tinsley E, Watkins SC, Khan SA.GTP-dependent polymerization of the tubulin-like RepX replication protein encoded by the pXO1 plasmid of Bacillus anthracis. Mol Microbiol. 2008 Feb;67(4):881-90.