INTRODUCTION
New ideas keep coming to satisfy all data accumulated regarding hook length control (1). Let us look at some of them and see if they are well brushed up as concept or just whim (3, 4).
(i) The molecular clock (8).
Length (L) and time (T) are independent parameters in physics. However, in our case, hook length L (in nanometers) and time T (in seconds) are intricately related to each other by the equation L = v′T, where v is the growth rate of the hook (in nanometers per second). The rate is possibly time-dependent, as we have previously shown by a statistical method (6). Thus, the molecular clock is a tautology. Then why do we bother with time? Let us stick to length alone (1, 3).
(ii) The statistical ruler (5).
This model assumes that FliK is continuously secreted into the culture medium. OK. The Cornelis group showed that probably only one FliK molecule is required to determine length (8a, 9). OK. We showed that a FliK variant which lacked the N-terminal region and thus was not secreted under any circumstances still controlled length when it was overproduced (2). What is the truth?
(iii) The proximal growth (7, 10).
Can a flagellum grow from the bottom? No! It was well established by the Asakura group in 1970s that the flagellum grows from the distal end of the filament. The concept called distal growth actually led us to further important discoveries such as the cap proteins and the type III secretion system (3, 4).
New ideas are welcome, but please do not forget the old concepts.
Footnotes
Published ahead of print 13 July 2012
This article is part of an ASM Dialog. To continue the conversation, see doi:10.1128/JB.00343-12, doi:10.1128/JB.06239-11, doi:10.1128/JB.06454-11.
REFERENCES
- 1. Aizawa S-I. 2012. Mystery of FliK in length control of the flagellar hook. J. Bacteriol. 194:4798–4800 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2. Hirano T, Shibata S, Ohnishi K, Tani T, Aizawa S-I. 2005. N-terminal signal region of FliK is dispensable for length control of the flagellar hook. Mol. Microbiol. 56:346–360 [DOI] [PubMed] [Google Scholar]
- 3. Hughes KT. 2012. Flagellar hook length is controlled by a secreted molecular ruler. J. Bacteriol. 194:4793–4796 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4. Hughes KT. 2012. Rebuttal: mystery of FliK in length control of the flagellar hook. J. Bacteriol. 194:4801. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 5. Keener JP. 2005. A model for length control of flagellar hooks of Salmonella typhimurium. J. Theor. Biol. 234:263–275 [DOI] [PubMed] [Google Scholar]
- 6. Koroyasu S, Yamazato M, Hirano T, Aizawa S-I. 1998. Kinetic analysis of the growth rate of the flagellar hook in Salmonella typhimurium by the population balance method. Biophys. J. 74:436–443 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 7. Marlovits TC, et al. 2006. Assembly of the inner rod determines needle length in the type III secretion injectisome. Nature 441:637–640 [DOI] [PubMed] [Google Scholar]
- 8. Moriya N, Minamino T, Hughes KT, Macnab RM, Namba K. 2006. The type III flagellar export specificity switch is dependent on FliK ruler and a molecular clock. J. Mol. Biol. 359:466–477 [DOI] [PubMed] [Google Scholar]
- 8a. Wagner S, Stenta M, Metzger LC, Dal Peraro M, Cornelis GR. 2010. Length control of the injectisome needle requires only one molecule of Yop secretion protein P (YscP). Proc. Natl. Acad. Sci. U. S. A. 107:13860–13865 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 9. Waters RC, O'Toole PW, Ryan KA. 2007. The FliK protein and flagellar hook-length control. Protein Sci. 16:769–780 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10. Wood SE, Jin J, Lloyd SA. 2008. YscP and YscU switch the substrate specificity of Yersinia type III secretion system by regulating export of the inner rod protein. J. Bacteriol. 190:4252–4262 [DOI] [PMC free article] [PubMed] [Google Scholar]