Structure and assembly of a paramyxovirus matrix protein.

Department of Biological Sciences, Purdue University, West Lafayette, IN 47907-2032, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 08/2012; 109(35):13996-4000. DOI: 10.1073/pnas.1210275109
Source: PubMed

ABSTRACT Many pleomorphic, lipid-enveloped viruses encode matrix proteins that direct their assembly and budding, but the mechanism of this process is unclear. We have combined X-ray crystallography and cryoelectron tomography to show that the matrix protein of Newcastle disease virus, a paramyxovirus and relative of measles virus, forms dimers that assemble into pseudotetrameric arrays that generate the membrane curvature necessary for virus budding. We show that the glycoproteins are anchored in the gaps between the matrix proteins and that the helical nucleocapsids are associated in register with the matrix arrays. About 90% of virions lack matrix arrays, suggesting that, in agreement with previous biological observations, the matrix protein needs to dissociate from the viral membrane during maturation, as is required for fusion and release of the nucleocapsid into the host's cytoplasm. Structure and sequence conservation imply that other paramyxovirus matrix proteins function similarly.

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    ABSTRACT: Human respiratory syncytial virus (RSV) is the most common cause of bronchiolitis and pneumonia in infants and elderly worldwide; however there is no licensed RSV vaccine or effective drug treatment available. The RSV Matrix (M) protein plays key roles in virus assembly and budding, but the protein interactions that govern budding of infectious virus are not known. In this study we focus on M protein and identify a key phosphorylation site (Thr(205)) in M that is critical for RSV infectious virus production. Recombinant virus with a nonphosphorylatable Alanine (Ala) residue at the site was markedly attenuated, whereas virus with a phosphomimetic Aspartate (Asp) resulted in a non-viable virus which could only be recovered with an additional mutation in M (Serine to Asparagine at position 220), strongly implying that Thr(205) is critical for viral infectivity. Experiments in vitro showed that mutation of Thr(205) does not affect M stability or the ability to form dimers, but implicate an effect on higher order oligomer assembly. In transfected and infected cells, Asp substitution of Thr(205) appeared to impair M oligomerization; typical filamentous structures still formed at the plasma membrane, but M assembly during the ensuing elongation process seemed to be impaired, resulting in shorter and more branched filaments as observed using EM. Our data thus imply for the first time that M oligomerization, regulated by negative charge at Thr(205), may be critical to production of infectious RSV. We show here for the first time that RSV M's role in virus assembly/release is strongly dependent on threonine (Thr(205)), a consensus site for CK2, which appears to play a key regulatory role in modulating M oligomerization and association with virus filaments. Our analysis indicates that T205 mutations do not impair M dimerization or virus-like filament formation per se, but rather the ability of M to assemble in ordered fashion on the viral filaments themselves. This appears to impact in turn upon the infectivity of released virus, rather than on virus production or release itself. Thus, M oligomerization would appear to be a target of interest for the development of anti-RSV agents; further, the recombinant T(205)-substituted mutant viruses described here would appear to be the first RSV mutants affected in viral maturation to our knowledge, and hence of considerable interest for vaccine approaches in the future.
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    ABSTRACT: In this issue of Structure, Leyrat and colleagues provide the first structural analysis of the human metapneumovirus (HMPV) matrix protein, a key regulator of viral assembly. Though structurally similar to other matrix proteins, two calcium binding sites suggest intriguing differences in regulation.
    Structure 01/2014; 22(1):5-7. · 5.99 Impact Factor
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    ABSTRACT: A quartet of attachment proteins and a trio of fusion protein subunits play the cell entry concert of parainfluenza viruses. While many of these viruses bind sialic acid to enter cells, wild type measles binds exclusively two tissue-specific proteins, the lymphatic receptor signaling lymphocytic activation molecule (SLAM), and the epithelial receptor nectin-4. SLAM binds near the stalk-head junction of the hemagglutinin. Nectin-4 binds a hydrophobic groove located between blades 4 and 5 of the hemagglutinin β-propeller head. The mutated vaccine strain hemagglutinin binds in addition the ubiquitous protein CD46, which explains attenuation. The measles virus entry concert has four movements. Andante misterioso: the virus takes over the immune system. Allegro con brio: it rapidly spreads in the upper airway's epithelia. 'Targeting' fugue: the versatile orchestra takes off. Presto furioso: the virus exits the host with thunder. Be careful: music is contagious.
    Current opinion in virology. 01/2014; 5C:16-23.

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