Dataset Information

Crystal structure of reovirus attachment protein ?1 in complex with sialylated oligosaccharides.

ABSTRACT: Many viruses attach to target cells by binding to cell-surface glycans. To gain a better understanding of strategies used by viruses to engage carbohydrate receptors, we determined the crystal structures of reovirus attachment protein ?1 in complex with ?-2,3-sialyllactose, ?-2,6-sialyllactose, and ?-2,8-di-siallylactose. All three oligosaccharides terminate in sialic acid, which serves as a receptor for the reovirus serotype studied here. The overall structure of ?1 resembles an elongated, filamentous trimer. It contains a globular head featuring a compact ?-barrel, and a fibrous extension formed by seven repeating units of a triple ?-spiral that is interrupted near its midpoint by a short ?-helical coiled coil. The carbohydrate-binding site is located between ?-spiral repeats two and three, distal from the head. In all three complexes, the terminal sialic acid forms almost all of the contacts with ?1 in an identical manner, while the remaining components of the oligosaccharides make little or no contacts. We used this structural information to guide mutagenesis studies to identify residues in ?1 that functionally engage sialic acid by assessing hemagglutination capacity and growth in murine erythroleukemia cells, which require sialic acid binding for productive infection. Our studies using ?1 mutant viruses reveal that residues 198, 202, 203, 204, and 205 are required for functional binding to sialic acid by reovirus. These findings provide insight into mechanisms of reovirus attachment to cell-surface glycans and contribute to an understanding of carbohydrate binding by viruses. They also establish a filamentous, trimeric carbohydrate-binding module that could potentially be used to endow other trimeric proteins with carbohydrate-binding properties.

SUBMITTER: Reiter DM

PROVIDER: S-EPMC3150272 | biostudies-literature | 2011 Aug

REPOSITORIES: biostudies-literature

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Crystal structure of reovirus attachment protein σ1 in complex with sialylated oligosaccharides.

Reiter Dirk M DM Frierson Johnna M JM Halvorson Elizabeth E EE Kobayashi Takeshi T Dermody Terence S TS Stehle Thilo T

PLoS pathogens 20110804 8

Many viruses attach to target cells by binding to cell-surface glycans. To gain a better understanding of strategies used by viruses to engage carbohydrate receptors, we determined the crystal structures of reovirus attachment protein σ1 in complex with α-2,3-sialyllactose, α-2,6-sialyllactose, and α-2,8-di-siallylactose. All three oligosaccharides terminate in sialic acid, which serves as a receptor for the reovirus serotype studied here. The overall structure of σ1 resembles an elongated, fila ...[more]

PMID: 21829363

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Project description:Molecular dynamics simulations were performed using the recently determined crystal structure of the reovirus attachment protein, sigma1. These studies were conducted to improve an understanding of two unique features of sigma1 structure: the protonation state of Asp(345), which is buried in the sigma1 trimer interface, and the flexibility of the protein at a defined region below the receptor-binding head domain. Three copies of aspartic acids Asp(345) and Asp(346) cluster in a solvent-inaccessible and hydrophobic region at the sigma1 trimer interface. These residues are hypothesized to mediate conformational changes in sigma1 during viral attachment or cell entry. Our results indicate that protonation of Asp(345) is essential to the integrity of the trimeric structure seen by x-ray crystallography, whereas deprotonation induces structural changes that destabilize the trimer interface. This finding was confirmed by electrostatic calculations using the finite difference Poisson-Boltzmann method. Earlier studies show that sigma1 can exist in retracted and extended conformations on the viral surface. Since protonated Asp(345) is necessary to form a stable, extended trimer, our results suggest that protonation of Asp(345) may allow for a structural transition from a partially detrimerized molecule to the fully formed trimer seen in the crystal structure. Additional studies were conducted to quantify the previously observed flexibility of sigma1 at a defined region below the receptor-binding head domain. Increased mobility was observed for three polar residues (Ser(291), Thr(292), and Ser(293)) located within an insertion between the second and third beta-spiral repeats of the crystallized portion of the sigma1 tail. These amino acids interact with water molecules of the solvent bulk and are responsible for oscillating movement of the head of approximately 50 degrees during 5 ns of simulations. This flexibility may facilitate viral attachment and also function in cell entry and disassembly. These findings provide new insights about the conformational dynamics of sigma1 that likely underlie the initiation of the reovirus infectious cycle.

Project description:Structural metastability of viral capsids is pivotal for viruses to survive in harsh environments and to undergo timely conformational changes required for cell entry. Mammalian orthoreovirus (reovirus) is a model to study capsid metastability. Following initial disassembly of the reovirus particle mediated by proteases, a metastable intermediate called the infectious subvirion particle (ISVP) is generated. Using a σ1 monoreassortant virus, we recently showed that σ1 properties affect its encapsidation on particles and the metastability of ISVPs. How metastability is impacted by σ1 and whether the lower encapsidation level of σ1 is connected to this property is unknown. To define a correlation between encapsidation of σ1 and ISVP stability, we generated mutant viruses with single amino acid polymorphisms in σ1 or those that contain chimeric σ1 molecules composed of σ1 portions from type 1 and type 3 reovirus strains. We found that under most conditions where σ1 encapsidation on the particle was lower, ISVPs displayed lower stability. Characterization of mutant viruses selected for enhanced stability via a forward genetic approach also revealed that in some cases, σ1 properties influence stability without influencing σ1 encapsidation. These data indicate that σ1 can also influence ISVP stability independent of its level of incorporation. Together, our work reveals an underappreciated effect of the σ1 attachment protein on the properties of the reovirus capsid. IMPORTANCE Reovirus particles are comprised of eight proteins. Among them, the reovirus σ1 protein functions engages cellular receptors. σ1 also influences the stability of an entry intermediate called ISVP. Here, we sought to define the basis of the link between σ1 properties and stability of ISVPs. Using variety of mutant strains, we determined that when virus preparations contain particles with a high amount of encapsidated σ1, ISVP stability is higher. Additionally, we identified portions of σ1 that impact its encapsidation and consequently the stability of ISVPs. We also determined that in some cases, σ1 properties alter stability of ISVPs without affecting encapsidation. This work highlights that proteins of these complex particles are arranged in an intricate, interconnected manner such that changing the properties of these proteins has a profound impact on the remainder of the particle.

Dataset Information

Crystal structure of reovirus attachment protein ?1 in complex with sialylated oligosaccharides.

Publications

Crystal structure of reovirus attachment protein σ1 in complex with sialylated oligosaccharides.

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