ABSTRACT
As self-assembling polyvalent nanoscale structures that can tolerate substantial genetic and chemical modification, virus-like particles are useful in a variety of fields. Here we describe the genetic modification and structural characterization of the Leviviridae PP7 capsid protein as a platform for the presentation of functional polypeptides. This particle was shown to tolerate the display of sequences from 1 kDa (a cell penetrating peptide) to 14 kDa (the Fc-binding double Z-domain) on its exterior surface as C-terminal genetic fusions to the coat protein. In addition, a dimeric construct allowed the presentation of exogenous loops between capsid monomers and the simultaneous presentation of two different peptides at different positions on the icosahedral structure. The PP7 particle is thereby significantly more tolerant of these types of polypeptide additions than Qß and MS2, the other Leviviridae-derived VLPs in common use.
Subject(s)
Capsid Proteins/chemistry , Capsid/chemistry , Leviviridae/chemistry , Peptide Library , Peptides/analysis , Amino Acid Sequence , Capsid/ultrastructure , Capsid Proteins/genetics , Capsid Proteins/ultrastructure , Leviviridae/genetics , Leviviridae/ultrastructure , Models, Molecular , Peptides/genetics , Protein EngineeringABSTRACT
Out of 177 surveyed bacteriophages, 161 (91%) are tailed and belong to the Myoviridae, Siphoviridae, and Podoviridae families (43, 55, and 59 viruses, respectively). Sixteen filamentous or isometric phages are members of the Inoviridae, Leviviridae, Microviridae, and Tectiviridae families (9%). Many tailed phages belong to established phage genera (P22, T1, T5, and T7), which are widespread in enterobacteria and other Gram-negatives of the Proteobacteria phylum.
Subject(s)
Salmonella Phages/ultrastructure , Salmonella/virology , Bacteriophage P22/ultrastructure , Bacteriophage Typing , Inoviridae/classification , Inoviridae/ultrastructure , Leviviridae/classification , Leviviridae/ultrastructure , Microscopy, Electron, Transmission , Microviridae/classification , Microviridae/ultrastructure , Myoviridae/classification , Myoviridae/ultrastructure , Podoviridae/classification , Podoviridae/ultrastructure , Salmonella Phages/classification , Siphoviridae/classification , Siphoviridae/ultrastructure , Tectiviridae/classification , Tectiviridae/ultrastructureABSTRACT
We solved the structures of the single-stranded RNA bacteriophages Qbeta, PP7 and AP205 by cryo-electron microscopy. On the outside, the symmetrized electron density maps resemble the previously described cryo-electron microscopy structure of MS2. RNA density is present inside the capsids, suggesting that the genomic RNA of Qbeta, PP7 and AP205, analogous to MS2, contains many coat protein-binding sites in addition to the hairpin on which assembly and packaging are initiated. All four bacteriophages harbour the same overall arrangement of the RNA, which is a unique combination of both triangles and pentagons. This combination has not been found in other icosahedral viruses, in which the RNA structures are either triangular or pentagonal. Strikingly, the unique RNA packing of the Leviviridae appears to deploy the most efficient method of RNA storage by obeying icosahedral symmetry.
Subject(s)
Cryoelectron Microscopy , Leviviridae/genetics , Leviviridae/ultrastructure , Nucleic Acid Conformation , RNA, Viral/chemistry , RNA, Viral/ultrastructure , Amino Acid Sequence , Genome, Viral/genetics , Molecular Sequence Data , Sequence Alignment , Viral Proteins/chemistry , Viral Proteins/genetics , Virion/genetics , Virion/ultrastructureABSTRACT
Bacteriophages are classified into one order and 13 families. Over 5100 phages have been examined in the electron microscope since 1959. At least 4950 phages (96%) are tailed. They constitute the order Caudovirales and three families. Siphoviridae or phages with long, noncontractile tails predominate (61% of tailed phages). Polyhedral, filamentous, and pleomorphic phages comprise less than 4% of bacterial viruses. Bacteriophages occur in over 140 bacterial or archaeal genera. Their distribution reflects their origin and bacterial phylogeny. Bacteriophages are polyphyletic, arose repeatedly in different hosts, and constitute 11 lines of descent. Tailed phages appear as monophyletic and as the oldest known virus group.
