scholarly journals Elucidation of the viral disassembly switch of tobacco mosaic virus

2019 ◽  
Author(s):  
Felix Weis ◽  
Maximilian Beckers ◽  
Iris von der Hocht ◽  
Carsten Sachse
Keyword(s):  
Tobacco Mosaic Virus ◽  
Mosaic Virus ◽  
Conformational Changes ◽  
Mechanistic Explanation ◽  
Text Book ◽  
Virus Structure ◽  
Close Proximity ◽  
Structural Details ◽  
Virus Model ◽  
Switch Mechanism

AbstractStable capsid structures of viruses protect viral RNA while they also require controlled disassembly for releasing the viral genome in the host cell. A detailed understanding of viral disassembly processes and the involved structural switches is still lacking. Biochemically, this process has been extensively studied using the tobacco mosaic virus model system and carboxylate interactions have been proposed to play a critical part in this process. Here, we present two cryo-EM structures of the helical TMV assembly at 2.1 and 2.0 Å resolution in conditions of high Ca2+concentration at low pH and in water. Based on our atomic models, we identified the conformational details of the disassembly switch mechanism: in high Ca2+/acidic pH environment the virion is stabilized between neighboring subunits through carboxyl groups E95 and E97 in close proximity to a Ca2+binding site. Upon increase in pH and lower Ca2+levels, mutual repulsion of the E95/E97 pair and Ca2+removal destabilize the network of interactions at lower radius and release the switch of virus disassembly. Our TMV structures revealed the conformational details for one of the reference systems of viral assembly/disassembly and provide the mechanistic explanation of a plethora of experimental results that were acquired over decades.Significance StatementTobacco mosaic virus presents the text-book example of virus structure and RNA release from a viral capsid through disassembly. Despite the wealth of structural and biochemical data on the assembly/disassembly properties generated from more than 80 years of research, the atomic-resolution structural details of the proposed conformational changes have not been resolved to date. The here determined high-resolution cryo-EM structures reveal the conformational details of the molecular disassembly switch. When the virus enters the cell, carboxylate repulsion and loss of calcium-ion coordination destabilize the switch region and can trigger RNA release through virus disassembly. The two determined structural states resolve a long-standing question on environment-driven virus disassembly switches.

The Mechanism of Aggregation of the Coat Protein of Tobacco Mosaic Virus. A Comparative Study on Vulgare and Mutant Proteins

1980 ◽  
Vol 35 (5-6) ◽  
pp. 482-494 ◽  
Author(s):  
Dieter Vogel ◽  
Guy D. de Marcillac ◽  
Leon Hirth ◽  
Kazuyuki Akasaka
Keyword(s):  
Ionic Strength ◽  
Coat Protein ◽  
Tobacco Mosaic Virus ◽  
Mosaic Virus ◽  
Conformational Changes ◽  
Salt Bridge ◽  
Cd Spectroscopy ◽  
Helical Conformation ◽  
Temperature Sensitive ◽  
Aggregation Behaviour

Abstract TMV vulgare, A 14, Ni 725; Two-and Three-Layer Aggregates, Structural and Mechanistic Differences, Inter-Subunit Interactions, Non-Specific Aggregations The aggregation behaviour of tobacco mosaic virus (TMV) protein vulgare was compared to that of two mutants, A 14 and Ni725, with amino acid exchanges localized in the coat protein at posi­ tions 107 (Thr → Met, in N i725) and 129 (lie → Thr, in both mutants). This behaviour, as meas­ ured by sedimentation, hydrogen ion titration, light-scattering, and near-UV absorption difference and circular dichroism (CD) spectroscopy, differs characteristically both in the range of the A-protein (pH 8) and near neutrality, whereas nuclear magnetic resonance (NMR) and far-UV CD point at only subtle, or no structural differences between the three strains. Near pH 8, the A-proteins of both mutants sediment nearly exclusively as 8 S aggregates, under conditions where vulgare protein forms a 4 S /8 S mixture (two-layer and three-layer aggregates, Vogel etal. in conditions where vulgare 4S aggregates dominate, both mutants sediment as a 4 S /8 S mixture. The average molecular weights of the 8S proteins corre­ spond to 12 (vulgare) to 15 (mutants) subunits. -Near neutrality both mutants titrate and polyme­ rize more cooperatively than vulgare protein; additionally, the pK(app.) of Ni 725 is shifted up­ wards, due to the higher a-helix forming potential of Met against Thr (pos. 107). Both mutants form large aggregates (> 200 S) of obviously helical conformation, by the uptake of one proton per subunit, whereas 20 S-disks constituting, under the same conditions, the stable entities in vul­ gare protein, are made only in minor amounts. These large mutant aggregates are remarkably more stable than the vulgare "overshoot" aggregates which transiently, too, may approach s-values and turbidities similar to the mutant aggregates; conformational changes, observed prior or in parallel to the formation of vulgare overshoot and disk aggregates, are significantly retarded in the large mutant aggregates. – Raising the ionic strength seems the only way to form mutant disks and stacks of disks (20-30 S) comparable to vulgare, pointing to the different pathways of disk formation, either at neutral pH or high ionic strength. – Evidence is given that the 8S aggregates of both mutant and vulgare proteins may behave similar in aggregation, the differences mainly being inserted by the 4S (two-layer) aggregates present in vulgare protein, which near neutrality seem responsible for the direct formation of (two-layer) disks. -The non-conservative exchange in po­ sition 129, altering the environment of Trp residues (52+17?), should weaken the "extended salt-bridge system" ("pairing") observed between the two layers of the disk (Bloomer et al., Nature, 1978). A competition is suggested between the strength of this pairing, and the binding of a third layer, regulating the mode of aggregation to two-layer, to three-layer, and to higher aggregates; this is corroborated by comparison with published results on temperature-sensitive (ts I) mutants and chemically modified proteins. – To explain the effects of residue 129 on the titration of the protein we suggest a mechanical analogy, made up of a balance between the charge and state of the "carboxyle cage" (Stubbs et al., Nature, 1977), as regulatory site, and the strength of the

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