Shimin Jianga,1, Akihiro Naritab,1, David Poppa,1,2, Umesh Goshdastidera,1, Lin Jie Leea, Ramanujam Srinivasanc,d, Mohan K. Balasubramanianc,e,f, Toshiro Odag,, Fujiet Koha, Mårten E. Larssona,h, Robert C. Robinsona,i,2
a Institute of Molecular and Cell Biology, A*STAR (Agency for Science, Technology and Research), Biopolis, Singapore 138673.
b Nagoya University Graduate School of Science, Structural Biology Research Center and Division of Biological Sciences, Furo-cho, Chikusa-ku, Nagoya, Japan.
c Mechanobiology Institute, National University of Singapore T-Lab, Engineering Drive 1, Singapore.
d National Institute of Science, Education and Research, Bhubaneswar, Orissa, 751005, India
e Temasek Life Sciences Laboratory, The National University of Singapore, 1 Research Link, Singapore.
f Warwick Medical School, University of Warwick, Coventry, CV4 7AL, England.
g Tokai Gakuin University, 5-68 Nakakirino-cho kagamihara, Gifu, Japan 504-8511.
h Department of Medical Biochemistry, Uppsala University, SE-75123, Uppsala, Sweden.
j Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore 117597.
1 these authors contributed equally to this work
2 Corresponding author
Published in PNAS on February 12th 2016.
Here we report the discovery of a bacterial DNA-segregating actin-like protein (BtParM) from Bacillus thuringiensis, which forms novel antiparallel, two-stranded, supercoiled, non-polar, helical filaments, as determined by electron microscopy. The BtParM filament features of supercoiling and forming antiparallel double strands are unique within the actin fold superfamily, and entirely different to the straight, double-stranded, polar, helical filaments of all other known ParMs and of eukaryotic F-actin. The BtParM polymers show dynamic assembly and subsequent disassembly in the presence of ATP. BtParR, the DNA-BtParM linking protein, stimulated ATP hydrolysis/phosphate release by BtParM and paired two supercoiled BtParM filaments to form a cylinder, comprised of four strands with inner and outer diameters of 57 Å and 145 Å, respectively. Thus, in this prokaryote, the actin fold has evolved to produce a filament system with comparable features to the eukaryotic chromosome-segregating microtubule.
Comparison of actin-like and tubulin-like filament structures. (A) Mammalian microtubule. (B) B. thuringiensis actin-like BtParM nanotubule. (C) B. thuringiensis actin-like BtParM filament. (D) Mammalian F-actin. (E) B. thuringiensis tubulin-like TubZ. The filament systems are depicted with ten protomers in each strand, with the exception of F-actin, which has eight. Top row: side views. Bottom row: top views.
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