The actin-like MreB proteins in Bacillus subtilis: a new turn
Arnaud Chastanet1,2, Rut Carballido-Lopez1,2
1
INRA, UMR1319 Micalis, F-78352 Jouy-en-Josas, France, 2AgroParisTech, UMR Micalis, F-78350 Jouy-en-Josas, France
TABLE OF CONTENTS
- 1. Abstract
- 2. A few generalities
- 3. The localization pattern of MreB: a revolution
- 3.1. A helical world
- 3.2. A revolutionary dynamics: the end of a helical world?
- 3.3. Colocalization of MreB isoforms
- 4. MreB proteins control cell morphogenesis
- 4.1. Inactivation of MreBs reveals their role in shape control
- 4.1.1. Conditional lethality of MreB mutants: Mg2+ to the rescue
- 4.1.2. Suppressor mutants of the MreB- and Mbl- lethal phenotype
- 4.2. Role of MreBs in control of bacterial cell wall biosynthesis
- 4.2.1. Cell wall synthesis in Bacillus subtilis
- 4.2.2. MreBs and sidewall elongation complexes
- 4.3. MreBs-associated morphogenetic factors in Bacillus subtilis
- 4.3.1. MreCD
- 4.3.2. RodA
- 4.3.3. LytE
- 4.3.4. EF-Tu
- 5. Additional cellular functions of Mreb homologs in B. Subtilis
- 5.1. Role in chromosome segregation
- 5.2. Role in organization of viral DNA replication
- 6. Structure and biochemical properties of MreB proteins
- 6.1. Biochemistry and structure
- 6.1.1. MreB1 of Thermotoga maritima
- 6.1.2. MreB of B. subtilis
- 6.2. Treadmilling
7. Open questions and concluding remarks
7.1. To be or not to be helical: that is the question
7.2. Mechanism underlying the control of CW synthesis by MreBs
7.3. Why have several mreB paralogs?
7.4. Additional functions of MreBs?
7.5. Concluding remarks
8. Annex 1: actin in brief
9. Annex 2: outlook of MreB in E. coli
9.1. MreB cellular organization
9.2. MreB and CW synthesis
9.3. MreB and chromosome segregation
9.4. Additional functions of MreB
10. Annex 3: outlook of MreB in C. crescentus
10.1. MreB cellular organization
10.2. MreB and CW synthesis
10.3. MreB and chromosome segregation
10.4. Additional functions of MreB
11. Annex 4: definitions
12. Acknowledgments
13. References
1. ABSTRACT
A decade ago, two breakthrough descriptions were reported: 1) the first helix-like protein localization pattern of MreB and its paralog Mbl in Bacillus subtilis and 2) the crystal structure of Thermotoga maritima MreB1, which was remarkably similar to that of actin. These discoveries strongly stimulated the field of bacterial development, leading to the identification of many new cytoskeletal proteins (1) and the publication of many studies describing the helical patterns of protein, DNA and even lipid domains. However, today, new breakthroughs are shaking up what had become a dogma. Instead of helical structures, MreBs appear to form discrete patches that move circumferentially around the cell, questioning the idea of MreB cables forming an actin-like cytoskeleton. Furthermore, increasing evidence of biochemical properties that are unlike the properties of actin suggest that the molecular behavior of MreB proteins may be different. The aim of this review is to summarize the current knowledge of the so-called "actin-like" MreB cytoskeleton through a discussion of the model Gram-positive bacterium B. subtilis and the most recent findings in this rapidly evolving research field.
