| Structural highlights
Function
[CAPSD_BPQBE] Capsid protein self-assembles to form an icosahedral capsid with a T=3 symmetry, about 26 nm in diameter, and consisting of 89 capsid proteins dimers (178 capsid proteins) (PubMed:27671640, PubMed:19913556). Involved in viral genome encapsidation through the interaction between a capsid protein dimer and the multiple packaging signals present in the RNA genome (PubMed:8943226, PubMed:27671640). Binding of the capsid proteins to the viral RNA induces a conformational change required for efficient T=3 shell formation (PubMed:19913556). The capsid contains also 1 copy of the A2 maturation protein (PubMed:27671640).[1] [2] [3] Acts as a translational repressor of viral replicase synthesis late in infection. This latter function is the result of capsid protein interaction with an RNA hairpin which contains the replicase ribosome-binding site.[4]
Publication Abstract from PubMed
In single-stranded RNA bacteriophages (ssRNA phages) a single copy of the maturation protein binds the genomic RNA (gRNA) and is required for attachment of the phage to the host pilus. For the canonical Allolevivirus Qbeta the maturation protein, A2, has an additional role as the lysis protein, by its ability to bind and inhibit MurA, which is involved in peptidoglycan biosynthesis. Here, we determined structures of Qbeta virions, virus-like particles, and the Qbeta-MurA complex using single-particle cryoelectron microscopy, at 4.7-A, 3.3-A, and 6.1-A resolutions, respectively. We identified the outer surface of the beta-region in A2 as the MurA-binding interface. Moreover, the pattern of MurA mutations that block Qbeta lysis and the conformational changes of MurA that facilitate A2 binding were found to be due to the intimate fit between A2 and the region encompassing the closed catalytic cleft of substrate-liganded MurA. Additionally, by comparing the Qbeta virion with Qbeta virus-like particles that lack a maturation protein, we observed a structural rearrangement in the capsid coat proteins that is required to package the viral gRNA in its dominant conformation. Unexpectedly, we found a coat protein dimer sequestered in the interior of the virion. This coat protein dimer binds to the gRNA and interacts with the buried alpha-region of A2, suggesting that it is sequestered during the early stage of capsid formation to promote the gRNA condensation required for genome packaging. These internalized coat proteins are the most asymmetrically arranged major capsid proteins yet observed in virus structures.
Structures of Qbeta virions, virus-like particles, and the Qbeta-MurA complex reveal internal coat proteins and the mechanism of host lysis.,Cui Z, Gorzelnik KV, Chang JY, Langlais C, Jakana J, Young R, Zhang J Proc Natl Acad Sci U S A. 2017 Oct 31;114(44):11697-11702. doi:, 10.1073/pnas.1707102114. Epub 2017 Oct 16. PMID:29078304[5]
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
References
- ↑ Basnak G, Morton VL, Rolfsson O, Stonehouse NJ, Ashcroft AE, Stockley PG. Viral genomic single-stranded RNA directs the pathway toward a T=3 capsid. J Mol Biol. 2010 Feb 5;395(5):924-36. doi: 10.1016/j.jmb.2009.11.018. Epub 2009, Nov 12. PMID:19913556 doi:http://dx.doi.org/10.1016/j.jmb.2009.11.018
- ↑ Gorzelnik KV, Cui Z, Reed CA, Jakana J, Young R, Zhang J. Asymmetric cryo-EM structure of the canonical Allolevivirus Qbeta reveals a single maturation protein and the genomic ssRNA in situ. Proc Natl Acad Sci U S A. 2016 Sep 26. pii: 201609482. PMID:27671640 doi:http://dx.doi.org/10.1073/pnas.1609482113
- ↑ Lim F, Spingola M, Peabody DS. The RNA-binding site of bacteriophage Qbeta coat protein. J Biol Chem. 1996 Dec 13;271(50):31839-45. PMID:8943226
- ↑ Lim F, Spingola M, Peabody DS. The RNA-binding site of bacteriophage Qbeta coat protein. J Biol Chem. 1996 Dec 13;271(50):31839-45. PMID:8943226
- ↑ Cui Z, Gorzelnik KV, Chang JY, Langlais C, Jakana J, Young R, Zhang J. Structures of Qbeta virions, virus-like particles, and the Qbeta-MurA complex reveal internal coat proteins and the mechanism of host lysis. Proc Natl Acad Sci U S A. 2017 Oct 31;114(44):11697-11702. doi:, 10.1073/pnas.1707102114. Epub 2017 Oct 16. PMID:29078304 doi:http://dx.doi.org/10.1073/pnas.1707102114
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