The Bacterial Cytoskeleton: an Intermediate Filament-Like Function in Cell Shape

Speaker: 林貞杏

Commentator: 吳俊忠 老師

Room: 601

Date: 3/3, 2004 15:00~16:00

Abstract:

A multitude of cell shape is encountered in the prokaryotic world, and this feature has been used as a taxonomical characteristic. But how bacteria come in these different shapes and what factors determine the shape of bacterial cells is not clear. Work over the past few years had indicated that MreB (actin-like protein) and FtsZ (tubulin-like protein) are essential for determining the rod shape and coccal-shaped of these bacteria¹. However, what factors are responsible for a curved bacterial morphology? In this study, the authors wanted to know how asymmetric shapes can be achieved in the curved bacteria. By screening the transposon insertion libraries of the naturally curved bacterium Caulobacter crescentus, they found that a gene, named creS, is essential for the curved and helical shapes of C. crescentus. The sequence of crescentin, the product of creS, has a distinct 7-residue repetitive pattern predicted to form coiled-coil structures, suggesting that crescentin might form an intracellular filament to support the curved shape. Immunofluorescence microscopy showed that a single filamentous structure along the concave side and the shortest helical path of the cell induced helical bacteria. The authors then found that although crescentin of a CreS-GFP strain can assemble into regular helical structure but fail to induce cell curvature, and the hybrid CreS-GFP/CreS strain can still form curved bacterial morphology. This suggested that the bulky GFP tag may prevent the proper localization of filament required for the curved morphology. Finally, they compared the amino acid sequence of crescentin with other known intermediate filament proteins and found that crescentin is an intermediate filament².

References:

1.    Van den Ent, F., Amos, L.A., and Lowel, J. Prokaryotic origin of the actin cytoskeleton. (2001). Nature 413, 39-44

2.    Ausmees, N., Kuhn, J.R., and Jacobs-Wagner, C. The Bacterial cytoskeleton: an intermediate filament-like function in cell shape. (2003) Cell 115, 705-713