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A protein with simultaneous capsid scaffolding and dsRNA-binding activities enhances the birnavirus capsid mechanical stability.

Mertens J, Casado S, Mata CP, Hernando-Pérez M, de Pablo PJ, Carrascosa JL, Castón JR - Sci Rep (2015)

Bottom Line: The IBDV population with the greatest RNP number (and best fitness) showed greatest capsid rigidity.These contacts involve interactions with capsid structural subunits that differ from the initial interactions during capsid assembly.Our results suggest that RNP dimers are the basic stabilization units of the virion, provide better understanding of multifunctional proteins, and highlight the duality of RNP as capsid-stabilizing and genetic information platforms.

View Article: PubMed Central - PubMed

Affiliation: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) Campus Cantoblanco, 28049 Madrid, Spain.

ABSTRACT
Viral capsids are metastable structures that perform many essential processes; they also act as robust cages during the extracellular phase. Viruses can use multifunctional proteins to optimize resources (e.g., VP3 in avian infectious bursal disease virus, IBDV). The IBDV genome is organized as ribonucleoproteins (RNP) of dsRNA with VP3, which also acts as a scaffold during capsid assembly. We characterized mechanical properties of IBDV populations with different RNP content (ranging from none to four RNP). The IBDV population with the greatest RNP number (and best fitness) showed greatest capsid rigidity. When bound to dsRNA, VP3 reinforces virus stiffness. These contacts involve interactions with capsid structural subunits that differ from the initial interactions during capsid assembly. Our results suggest that RNP dimers are the basic stabilization units of the virion, provide better understanding of multifunctional proteins, and highlight the duality of RNP as capsid-stabilizing and genetic information platforms.

No MeSH data available.


Related in: MedlinePlus

RNP dimers are the basic stabilization units of the IBDV capsid.Scheme of the IBDV capsid showing structural components involved in stabilizing interactions. When VP3 is found alone inside the capsid (as in empty VLP, E1 and E2) or in the presence of ssRNA (as in full VLP), contacts with VP2 (red X) are weak or non-existent. When dsRNA is present, these contacts are more intense (small double arrowheads), presumably because dsRNA-bound VP3 acquire the correct conformation to establish a stronger interaction with VP2 (left). Mature IBDV virions, represented by E5-E6 capsids, are polyploid and contain four packaged dsRNA segments organized as RNP. In this case, RNP are organized internally as dimers; in this oligomeric state, VP3 acquires a conformation with which it establishes strong interactions with the inner surface of the viral shell. This structural organization of the genome explains the stepwise disruption profile during mechanical fatigue (shell thickness is ~10 nm based on three-dimensional cryo-EM analysis).
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f5: RNP dimers are the basic stabilization units of the IBDV capsid.Scheme of the IBDV capsid showing structural components involved in stabilizing interactions. When VP3 is found alone inside the capsid (as in empty VLP, E1 and E2) or in the presence of ssRNA (as in full VLP), contacts with VP2 (red X) are weak or non-existent. When dsRNA is present, these contacts are more intense (small double arrowheads), presumably because dsRNA-bound VP3 acquire the correct conformation to establish a stronger interaction with VP2 (left). Mature IBDV virions, represented by E5-E6 capsids, are polyploid and contain four packaged dsRNA segments organized as RNP. In this case, RNP are organized internally as dimers; in this oligomeric state, VP3 acquires a conformation with which it establishes strong interactions with the inner surface of the viral shell. This structural organization of the genome explains the stepwise disruption profile during mechanical fatigue (shell thickness is ~10 nm based on three-dimensional cryo-EM analysis).

Mentions: RNase digestion assays of purified RNP suggested that VP3 shields dsRNA homogeneously11, and we assume that dsRNA-bound VP3 probably mediates the mechanical resilience of the IBDV capsid, although dsRNA might also be involved. VP3, alone or in the presence of nonspecific cellular ssRNA (free or ssRNA-bound), does not increase capsid rigidity. These results imply that VP3 acquires a conformation competent for interaction with VP2 only by binding to dsRNA (Fig. 5). The VP2-VP3 interaction differs from pVP2-VP3 interactions during capsid assembly (see below). Three-dimensional reconstructions of virions showed only capsid densities corresponding to VP2, with no trace of residual VP3-related densities946, which suggests that the VP2-VP3 interactions detected in AFM analysis are random and/or stable but irregular. Study of VP3 mutants that partially affect capsid stability without altering other activities such as dsRNA binding could identify the VP3 segments involved in post-assembly capsid stabilization.


A protein with simultaneous capsid scaffolding and dsRNA-binding activities enhances the birnavirus capsid mechanical stability.

Mertens J, Casado S, Mata CP, Hernando-Pérez M, de Pablo PJ, Carrascosa JL, Castón JR - Sci Rep (2015)

RNP dimers are the basic stabilization units of the IBDV capsid.Scheme of the IBDV capsid showing structural components involved in stabilizing interactions. When VP3 is found alone inside the capsid (as in empty VLP, E1 and E2) or in the presence of ssRNA (as in full VLP), contacts with VP2 (red X) are weak or non-existent. When dsRNA is present, these contacts are more intense (small double arrowheads), presumably because dsRNA-bound VP3 acquire the correct conformation to establish a stronger interaction with VP2 (left). Mature IBDV virions, represented by E5-E6 capsids, are polyploid and contain four packaged dsRNA segments organized as RNP. In this case, RNP are organized internally as dimers; in this oligomeric state, VP3 acquires a conformation with which it establishes strong interactions with the inner surface of the viral shell. This structural organization of the genome explains the stepwise disruption profile during mechanical fatigue (shell thickness is ~10 nm based on three-dimensional cryo-EM analysis).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4559658&req=5

f5: RNP dimers are the basic stabilization units of the IBDV capsid.Scheme of the IBDV capsid showing structural components involved in stabilizing interactions. When VP3 is found alone inside the capsid (as in empty VLP, E1 and E2) or in the presence of ssRNA (as in full VLP), contacts with VP2 (red X) are weak or non-existent. When dsRNA is present, these contacts are more intense (small double arrowheads), presumably because dsRNA-bound VP3 acquire the correct conformation to establish a stronger interaction with VP2 (left). Mature IBDV virions, represented by E5-E6 capsids, are polyploid and contain four packaged dsRNA segments organized as RNP. In this case, RNP are organized internally as dimers; in this oligomeric state, VP3 acquires a conformation with which it establishes strong interactions with the inner surface of the viral shell. This structural organization of the genome explains the stepwise disruption profile during mechanical fatigue (shell thickness is ~10 nm based on three-dimensional cryo-EM analysis).
Mentions: RNase digestion assays of purified RNP suggested that VP3 shields dsRNA homogeneously11, and we assume that dsRNA-bound VP3 probably mediates the mechanical resilience of the IBDV capsid, although dsRNA might also be involved. VP3, alone or in the presence of nonspecific cellular ssRNA (free or ssRNA-bound), does not increase capsid rigidity. These results imply that VP3 acquires a conformation competent for interaction with VP2 only by binding to dsRNA (Fig. 5). The VP2-VP3 interaction differs from pVP2-VP3 interactions during capsid assembly (see below). Three-dimensional reconstructions of virions showed only capsid densities corresponding to VP2, with no trace of residual VP3-related densities946, which suggests that the VP2-VP3 interactions detected in AFM analysis are random and/or stable but irregular. Study of VP3 mutants that partially affect capsid stability without altering other activities such as dsRNA binding could identify the VP3 segments involved in post-assembly capsid stabilization.

Bottom Line: The IBDV population with the greatest RNP number (and best fitness) showed greatest capsid rigidity.These contacts involve interactions with capsid structural subunits that differ from the initial interactions during capsid assembly.Our results suggest that RNP dimers are the basic stabilization units of the virion, provide better understanding of multifunctional proteins, and highlight the duality of RNP as capsid-stabilizing and genetic information platforms.

View Article: PubMed Central - PubMed

Affiliation: Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA Nanociencia) Campus Cantoblanco, 28049 Madrid, Spain.

ABSTRACT
Viral capsids are metastable structures that perform many essential processes; they also act as robust cages during the extracellular phase. Viruses can use multifunctional proteins to optimize resources (e.g., VP3 in avian infectious bursal disease virus, IBDV). The IBDV genome is organized as ribonucleoproteins (RNP) of dsRNA with VP3, which also acts as a scaffold during capsid assembly. We characterized mechanical properties of IBDV populations with different RNP content (ranging from none to four RNP). The IBDV population with the greatest RNP number (and best fitness) showed greatest capsid rigidity. When bound to dsRNA, VP3 reinforces virus stiffness. These contacts involve interactions with capsid structural subunits that differ from the initial interactions during capsid assembly. Our results suggest that RNP dimers are the basic stabilization units of the virion, provide better understanding of multifunctional proteins, and highlight the duality of RNP as capsid-stabilizing and genetic information platforms.

No MeSH data available.


Related in: MedlinePlus