Intrinsic versus imposed curvature in cyclical oligomers: the portal protein of bacteriophage SPP1.
Large cyclical oligomers may be formed by (curvi-) linear polymerization of monomers until the n(th) monomer locks in with the first member of the chain. The subunits in incomplete structures exhibit a natural curvature with respect to each other which can be perturbed when the oligomer closes cyclically. Using cryo-electron microscopy and multivariate statistical image processing we report herein a direct structural observation of this effect. A sub-population (approximately 15%) of incomplete oligomers was found within a sample of SPP1 bacteriophage portal proteins embedded in vitreous ice. Whereas the curvature between adjacent subunits of the closed circular 13-fold symmetric oligomer is 27.7 degrees, in these incomplete oligomers the angle is only 25.8 degrees, a value which almost allows for a 14-subunit cyclical arrangement. A simple model for the association of large cyclical oligomers is suggested by our data.
Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany.
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van Heel
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Orlova
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Dube
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Tavares
D008854:Microscopy, Electron; D008958:Models, Molecular; D015999:Multivariate Analysis; D011487:Protein Conformation; D054334:Viral Regulatory and Accessory Proteins / Q000737:chemistry* / Q000648:ultrastructure
D054334:Viral Regulatory and Accessory Proteins; C073671:SPP1 pac region protein, Bacteriophage SPP1