| Literature References | 1. JONES, L.J., CARBALLIDO-LOPEZ, R. AND ERRINGTON, J.
Control of cell shape in bacteria: helical, actin-like filaments in
Bacillus subtilis.
CELL 104 913-922 (2001).
2. VAN DEN ENT, F., AMOS, L.A. AND LOWE, J.
Prokaryotic origin of the actin cytoskeleton.
NATURE 413 39-44 (2001).
3. VAN DEN ENT, F., AMOS, L.A. AND LOWE, J.
Bacterial ancestry of actin and tubulin.
CURR.OPIN.MICROBIOL. 4 634-638 (2001).
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| Documentation | Bacterial cell shape varies greatly between species, and characteristic
morphologies are used for identification purposes. In addition to individual
cell shape, the way in which groups of cells are arranged is also typical of
some bacterial species, especially Gram-positive coccoids [1]. Microscopy
has proved its value in the classification and diagnosis of species based
on cell shape.
For many years, it was believed that micro-organisms with other than
spheroidal cell shapes maintained morphology by means of their external cell
walls. Recently, however, studies of the Gram-positive rod Bacillus subtilis
have revealed two related genes that are essential for the integrity of cell
morphogenesis [1]. Termed mreB and mbl, the gene products localise close to
the cell surface, forming filamentous helical structures [1,2]. Many
homologues have been found in diverse bacterial groups, suggesting a common
ancestor [2].
The crystal structure of MreB from Thermotoga maritima has been resolved
using X-ray crystallography [2]. It consists of 19 beta-strands and 15 alpha-
helices, and shows remarkable structural similarity to eukaryotic actin [2].
MreB crystals also contain proto-filaments, with individual proteins
assembling into polymers like F-actin, in the same orientation. It is
hypothesised therefore, that MreB was the forerunner of actin in early
eukaryotes [2,3].
Another bacterial protein involved in morphogenesis and cell division, FtsZ,
shows structural and functional resemblance to another eukaryotic cell
cytoskeletal moiety, tubulin. [3]. This indicates a prokaryotic origin for
tubulin as well as actin [3].
SHAPEPROTEIN is a 5-element fingerprint that provides a signature for the
bacterial cell shape determinant MreB/Mbl proteins. The fingerprint was
derived from an initial alignment of 7 sequences: the motifs were drawn
from conserved regions spanning virtually the full alignment length - motif
1 spans alpha-helix 1 and the N-terminus of beta-strand 6; motif 2 spans
strands 7, 8 and the N-terminus of helix 2; motif 3 encompasses strand 10
and helix 4; motif 4 spans helix 5 and strand 14; and motif 5 spans helices
12 and 13, and strand 18. Three iterations on SPTR40_18f were required to
reach convergence, at which point a true set comprising 34 sequences was
identified.
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