1qbe
BACTERIOPHAGE Q BETA CAPSID
Structural highlights
FunctionCAPSD_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] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedBACKGROUND: The capsid protein subunits of small RNA bacteriophages form a T = 3 particle upon assembly and RNA encapsidation. Dimers of the capsid protein repress translation of the replicase gene product by binding to the ribosome binding site and this interaction is believed to initiate RNA encapsidation. We have determined the crystal structure of phage Q beta with the aim of clarifying which factors are the most important for particle assembly and RNA interaction in the small phages. RESULTS: The crystal structure of bacteriophage Q beta determined at 3.5 A resolution shows that the capsid is stabilized by disulfide bonds on each side of the flexible loops that are situated around the fivefold and quasi-sixfold axes. As in other small RNA phages, the protein capsid is constructed from subunits which associate into dimers. A contiguous ten-stranded antiparallel beta sheet facing the RNA is formed in the dimer. The disulfide bonds lock the constituent dimers of the capsid covalently in the T = 3 lattice. CONCLUSIONS: The unusual stability of the Q beta particle is due to the tight dimer interactions and the disulfide bonds linking each dimer covalently to the rest of the capsid. A comparison with the structure of the related phage MS2 shows that although the fold of the Q beta coat protein is very similar, the details of the protein-protein interactions are completely different. The most conserved region of the protein is at the surface, which, in MS2, is involved in RNA binding. The crystal structure of bacteriophage Q beta at 3.5 A resolution.,Golmohammadi R, Fridborg K, Bundule M, Valegard K, Liljas L Structure. 1996 May 15;4(5):543-54. PMID:8736553[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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