Prokaryotic cytoskeleton pdf

These independent studies each purified FtsZ protein from an Escherichia coli expression system and demonstrated that it bound and hydrolyzed GTP. That sequence, known as the tubulin signature sequence, was believed to be involved in the binding of GTP in the tubulins. The three groups all concluded that the GTP-binding site of FtsZ appeared to be related to that of tubulins. A year earlier, before any link to tubulin was known, Bi and Lutkenhaus were the first to propose that FtsZ might be a cytoskeletal protein.

They used immuno—electron microscopy to show that FtsZ localized to the invaginating septum in dividing E. In particular, de Boer et al. A subsequent study by Mukherjee and Lutkenhaus provided two major advances. First, they demonstrated that purified FtsZ could assemble in vitro into filamentous polymers. This was strong support for the proposed role as cytoskeleton. Our laboratory took up the question of in vitro assembly and showed that FtsZ assembled in vitro into sheets of protofilaments and mini-rings that were similar to tubulin polymers Erickson et al.

They had an identical complex fold, which is the ultimate test of homology. It turns out that FtsZ is not the only tubulin homologue in prokaryotes. Many archaeans have up to five FtsZ homologues, some with very divergent sequences that likely serve functions other than cell division.

The discovery of bacterial actins was complicated by the homology of actin to other protein families. Protein homology means shared ancestry. Sometimes, this is indicated by amino acid sequence identity, but often this sequence identity is too weak to recognize. The most definitive demonstration of homology is from protein structure. When the x-ray structure of actin was determined Kabsch et al.

Because this fold is so complex yet was shared so precisely, it was concluded that the three shared a common ancestry.

Actin, hexokinase, and Hsp70 are homologues and are considered to be members of an actin superfamily. Note that homology does not imply common function. Probably the original protein in this family was the sugar kinase, which underwent gene duplications that evolved into a chaperonin and separately into a protein that could assemble cytoskeletal filaments, actin.

The first strong suggestion for actin homologues in bacteria was a theoretical study by Bork et al. They used the recent x-ray structures of actin, hexokinase, and Hsp70 to do a structure-based sequence alignment, which identified four short signature sequences that were conserved across the superfamily.

These bacterial proteins were closest in sequence to Hsp70 and actin rather than the sugar kinases and were therefore candidates for bacterial actin. Experimental confirmation that MreB was an actin homologue finally came 9 years later.

Jones et al. Van den Ent et al. Their major discovery was x-ray crystallography, which showed that MreB had the actin fold and was assembled in the crystals into actin-like filaments. Later work has discovered multiple prokaryotic actins with a variety of cytoskeletal functions, although the functions of most are unknown. An interesting irony is that roles of tubulin and actin have somewhat switched from bacteria to eukaryotes.

FtsZ forms the cytokinetic ring in bacteria, whereas actin provides the major cytoskeletal framework in eukaryotes. Some bacterial plasmid actins function for nucleoid segregation, a role performed by microtubules in eukaryotes.

However, some TubZ filaments also function for plasmid segregation. A global conclusion would be that once a protein has evolved the ability to assemble cytoskeletal filaments, these can be modified to perform a wide range of useful and sometimes overlapping cellular functions. DOI: National Center for Biotechnology Information , U.

Journal List Mol Biol Cell v. Mol Biol Cell. Harold P. Keith G. Kozminski, Monitoring Editor University of Virginia. RayChaudhuri, D. Escherichia coli cell-division gene ftsZ encodes a novel GTP-binding protein. Nature , — Mukherjee, A. Escherichia coli cell division protein FtsZ is a guanine nucleotide binding protein.

Natl Acad. USA 90 , — Crystal structure of the bacterial cell-division protein FtsZ. Article Google Scholar. Jones, L. Control of cell shape in bacteria: helical, actin-like filaments in Bacillus subtilis. Cell , — Prokaryotic origin of the actin cytoskeleton.

Nature , 39—44 Ausmees, N. The bacterial cytoskeleton: an intermediate filament-like function in cell shape. Download references. You can also search for this author in PubMed Google Scholar. Reprints and Permissions. Nath, D. The prokaryotic cytoskeleton. Nat Rev Mol Cell Biol 9, s19 Download citation. Published : 01 December Issue Date : May Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article.

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