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Two Novel Amyloid Proteins, RopA and RopB, from the Root Nodule Bacterium Rhizobium leguminosarum

1
Laboratory for Proteomics of Supra-Organismal Systems, All-Russia Research Institute for Agricultural Microbiology (ARRIAM), 196608 St. Petersburg, Russia
2
Faculty of Biology, St. Petersburg State University (SPbSU), 199034 St. Petersburg, Russia
3
Laboratory of Structural Dynamics, Stability and Folding of Proteins, Institute of Cytology of the Russian Academy of Sciences, 194064 St. Petersburg, Russia
4
Laboratory of Cell Morphology, Institute of Cytology of the Russian Academy of Sciences, 194064 St. Petersburg, Russia
5
Research Resource Center "Molecular and Cell Technologies", Research Park, St. Petersburg State University (SPbSU), 199034 St. Petersburg, Russia
6
Department of Biotechnology, All-Russia Research Institute for Agricultural Microbiology (ARRIAM), St. Petersburg, 196608, Russia
7
Komarov Botanical Institute RAS, 197376 Komarov Botanical Institute RAS, Russia
8
Peter the Great St. Petersburg Polytechnic University, 195251 St. Petersburg, Russia
*
Author to whom correspondence should be addressed.
These authors contributed equally to this work.
Biomolecules 2019, 9(11), 694; https://doi.org/10.3390/biom9110694
Received: 1 September 2019 / Revised: 29 October 2019 / Accepted: 31 October 2019 / Published: 4 November 2019
(This article belongs to the Section Biochemistry)
Amyloids represent protein fibrils with a highly ordered spatial structure, which not only cause dozens of incurable human and animal diseases but also play vital biological roles in Archaea, Bacteria, and Eukarya. Despite the fact that association of bacterial amyloids with microbial pathogenesis and infectious diseases is well known, there is a lack of information concerning the amyloids of symbiotic bacteria. In this study, using the previously developed proteomic method for screening and identification of amyloids (PSIA), we identified amyloidogenic proteins in the proteome of the root nodule bacterium Rhizobium leguminosarum. Among 54 proteins identified, we selected two proteins, RopA and RopB, which are predicted to have β-barrel structure and are likely to be involved in the control of plant-microbial symbiosis. We demonstrated that the full-length RopA and RopB form bona fide amyloid fibrils in vitro. In particular, these fibrils are β-sheet-rich, bind Thioflavin T (ThT), exhibit green birefringence upon staining with Congo Red (CR), and resist treatment with ionic detergents and proteases. The heterologously expressed RopA and RopB intracellularly aggregate in yeast and assemble into amyloid fibrils at the surface of Escherichia coli. The capsules of the R. leguminosarum cells bind CR, exhibit green birefringence, and contain fibrils of RopA and RopB in vivo.
Keywords: amyloid; fibril; RopA; RopB; outer membrane protein; porin; root nodule; bacteria; plant–microbial interaction; Rhizobium leguminosarum amyloid; fibril; RopA; RopB; outer membrane protein; porin; root nodule; bacteria; plant–microbial interaction; Rhizobium leguminosarum
MDPI and ACS Style

Kosolapova, A.O.; Belousov, M.V.; Sulatskaya, A.I.; Belousova, M.E.; Sulatsky, M.I.; Antonets, K.S.; Volkov, K.V.; Lykholay, A.N.; Shtark, O.Y.; Vasileva, E.N.; Zhukov, V.A.; Ivanova, A.N.; Zykin, P.A.; Kuznetsova, I.M.; Turoverov, K.K.; Tikhonovich, I.A.; Nizhnikov, A.A. Two Novel Amyloid Proteins, RopA and RopB, from the Root Nodule Bacterium Rhizobium leguminosarum. Biomolecules 2019, 9, 694.

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