The head of bacteriophage T4 is a prolate icosahedron with one unique portal vertex to which the phage tail is attached. The three-dimensional structure of mature bacteriophage T4 head has been ...determined to 22-Å resolution by using cryo-electron microscopy. The T4 capsid has a hexagonal surface lattice characterized by the triangulation numbers Tend=13 laevo for the icosahedral caps and T mid=20 for the midsection. Hexamers of the major capsid protein gene product (gp)23* and pentamers of the vertex protein gp24*, as well as the outer surface proteins highly antigenic outer capsid protein (hoc) and small outer capsid protein (soc), are clearly evident in the reconstruction. The size and shape of the gp23* hexamers are similar to the major capsid protein organization of bacteriophage HK97. The binding sites and shape of the hoc and soc proteins have been established by analysis of the soc- and hoc-soc- T4 structures.
Bacteriophage T4 has a very efficient mechanism for infecting cells. The key component of this process is the baseplate, located at the end of the phage tail, which regulates the interaction of the ...tail fibres and the DNA ejection machine. A complex of gene product (gp) 5 (63K) and gp27 (44K), the central part of the baseplate, is required to penetrate the outer cell membrane of Escherichia coli and to disrupt the intermembrane peptidoglycan layer, promoting subsequent entry of phage DNA into the host. We present here a crystal structure of the (gp5-gp27)3 321K complex, determined to 2.9 resolution and fitted into a cryo-electron microscopy map at 17 resolution of the baseplate-tail tube assembly. The carboxy-terminal domain of gp5 is a triple-stranded β-helix that forms an equilateral triangular prism, which acts as a membrane-puncturing needle. The middle lysozyme domain of gp5, situated on the periphery of the prism, serves to digest the peptidoglycan layer. The amino-terminal, antiparallel β-barrel domain of gp5 is inserted into a cylinder formed by three gp27 monomers, which may serve as a channel for DNA ejection.
The contractile tail of bacteriophage T4 undergoes major structural transitions when the virus attaches to the host cell surface. The baseplate at the distal end of the tail changes from a hexagonal ...to a star shape. This causes the sheath around the tail tube to contract and the tail tube to protrude from the baseplate and pierce the outer cell membrane and the cell wall before reaching the inner cell membrane for subsequent viral DNA injection. Analogously, the T4 tail can be contracted by treatment with 3 M urea. The structure of the T4 contracted tail, including the head-tail joining region, has been determined by cryo-electron microscopy to 17 Å resolution. This 1200 Å-long, 20 MDa structure has been interpreted in terms of multiple copies of its approximately 20 component proteins. A comparison with the metastable hexagonal baseplate of the mature virus shows that the baseplate proteins move as rigid bodies relative to each other during the structural change.
Structure and morphogenesis of bacteriophage T4 Leiman, P G; Kanamaru, S; Mesyanzhinov, V V ...
Cellular and molecular life sciences : CMLS,
11/2003, Letnik:
60, Številka:
11
Journal Article
Recenzirano
Bacteriophage T4 is one of the most complex viruses. More than 40 different proteins form the mature virion, which consists of a protein shell encapsidating a 172-kbp double-stranded genomic DNA, a ...'tail,' and fibers, attached to the distal end of the tail. The fibers and the tail carry the host cell recognition sensors and are required for attachment of the phage to the cell surface. The tail also serves as a channel for delivery of the phage DNA from the head into the host cell cytoplasm. The tail is attached to the unique 'portal' vertex of the head through which the phage DNA is packaged during head assembly. Similar to other phages, and also herpes viruses, the unique vertex is occupied by a dodecameric portal protein, which is involved in DNA packaging.
Gene product (gp) 24 of bacteriophage T4 forms the pentameric vertices of the capsid. Using x-ray crystallography, we found the principal domain of gp24 to have a polypeptide fold similar to that of ...the HK97 phage capsid protein plus an additional insertion domain. Fitting gp24 monomers into a cryo-EM density map of the mature T4 capsid suggests that the insertion domain interacts with a neighboring subunit, effecting a stabilization analogous to the covalent crosslinking in the HK97 capsid. Sequence alignment and genetic data show that the folds of gp24 and the hexamer-forming capsid protein, gp23*, are similar. Accordingly, models of gp24* pentamers, gp23* hexamers, and the whole capsid were built, based on a cryo-EM image reconstruction of the capsid. Mutations in gene 23 that affect capsid shape map to the capsomer's periphery, whereas mutations that allow gp23 to substitute for gp24 at the vertices modify the interactions between monomers within capsomers. Structural data show that capsid proteins of most tailed phages, and some eukaryotic viruses, may have evolved from a common ancestor.
The baseplate of bacteriophage T4 is a multiprotein molecular machine that controls host cell recognition, attachment, tail sheath contraction and viral DNA ejection. We report here the ...three-dimensional structure of the baseplate-tail tube complex determined to a resolution of 12 A by cryoelectron microscopy. The baseplate has a six-fold symmetric, dome-like structure approximately 520 A in diameter and approximately 270 A long, assembled around a central hub. A 940 A-long and 96 A-diameter tail tube, coaxial with the hub, is connected to the top of the baseplate. At the center of the dome is a needle-like structure that was previously identified as a cell puncturing device. We have identified the locations of six proteins with known atomic structures, and established the position and shape of several other baseplate proteins. The baseplate structure suggests a mechanism of baseplate triggering and structural transition during the initial stages of T4 infection.
Bacteriophage φKZ is a giant virus that efficiently infects
Pseudomonas aeruginosa strains pathogenic to human and, therefore, it is attractive for phage therapy. We present here the complete φKZ ...genome sequence and a preliminary analysis of its genome structure. The 280,334 bp genome is a linear, circularly permutated and terminally redundant, A+T-rich double-stranded DNA molecule. The φKZ DNA has no detectable sequence homology to other viruses and microorganisms, and it does not contain
NotI,
PstI,
SacI,
SmaI,
XhoI, and
XmaIII endonuclease restriction sites. The genome has 306 open reading frames (ORFs) varying in size from 50 to 2237 amino acid residues. According to the orientation of transcription, ORFs are apparently organized into clusters and most have a clockwise direction. The φKZ genome also encodes six tRNAs specific for Met (AUG), Asn (AAC), Asp (GAC), Leu (TTA), Thr (ACA), and Pro (CCA). A putative promoter sequence containing a TATATTAC block was identified. Most potential stem-loop transcription terminators contain the tetranucleotide UUCG loops. Some genes may be assigned as phage-encoded RNA polymerase subunits. Only 59 φKZ gene products exhibit similarity to proteins of known function from a diversity of organisms. Most of these conserved gene products, such as dihydrofolate reductase, ribonucleoside diphosphate reductase, thymidylate synthase, thymidylate kinase, and deoxycytidine triphosphate deaminase are involved in nucleotide metabolism. However, no virus-encoded DNA polymerase, DNA replication-associated proteins, or single-stranded DNA-binding protein were found based on amino acid homology, and they may therefore be strongly divergent from known homologous proteins. Fifteen φKZ gene products show homology to proteins of pathogenic organisms, including
Mycobacterium tuberculosis, Haemophilus influenzae,
Listeria sp.,
Rickettsia prowazakeri,and
Vibrio choleraethat must be considered before using this phage as a therapeutic agent. The φKZ coat contains at least 40 polypeptides, and several proteins are cleaved during virus assembly in a way similar to phage T4. Eleven φKZ-encoded polypeptides are related to proteins of other bacteriphages that infect a variety of hosts. Among these are four gene products that contain a putative intron-encoded endonuclease harboring the H-N-H motif common to many double-stranded DNA phages. These observations provide evidence that phages infecting diverse hosts have had access to a common genetic pool. However, limited homology on the DNA and protein levels indicates that bacteriophage φKZ represents an evolutionary distinctive branch of the
Myoviridaefamily.
Bacteriophage T4 and related viruses have a contractile tail that serves as an efficient mechanical device for infecting bacteria. A three-dimensional cryo-EM reconstruction of the mature T4 tail ...assembly at 15-A resolution shows the hexagonal dome-shaped baseplate, the extended contractile sheath, the long tail fibers attached to the baseplate and the collar formed by six whiskers that interact with the long tail fibers. Comparison with the structure of the contracted tail shows that tail contraction is associated with a substantial rearrangement of the domains within the sheath protein and results in shortening of the sheath to about one-third of its original length. During contraction, the tail tube extends beneath the baseplate by about one-half of its total length and rotates by 345 degrees , allowing it to cross the host's periplasmic space.
The contractile tail of bacteriophage T4 is a molecular machine that facilitates very high viral infection efficiency. Its major component is a tail sheath, which contracts during infection to less ...than half of its initial length. The sheath consists of 138 copies of the tail sheath protein, gene product (gp) 18, which surrounds the central non‐contractile tail tube. The contraction of the sheath drives the tail tube through the outer membrane, creating a channel for the viral genome delivery. A crystal structure of about three quarters of gp18 has been determined and was fitted into cryo‐electron microscopy reconstructions of the tail sheath before and after contraction. It was shown that during contraction, gp18 subunits slide over each other with no apparent change in their structure.
The bacteriophage T4 DNA injection machine Rossmann, Michael G; Mesyanzhinov, Vadim V; Arisaka, Fumio ...
Current opinion in structural biology,
04/2004, Letnik:
14, Številka:
2
Journal Article
Recenzirano
The tail of bacteriophage T4 consists of a contractile sheath surrounding a rigid tube and terminating in a multiprotein baseplate, to which the long and short tail fibers of the phage are attached. ...Upon binding of the fibers to their cell receptors, the baseplate undergoes a large conformational switch, which initiates sheath contraction and culminates in transfer of the phage DNA from the capsid into the host cell through the tail tube. The baseplate has a dome-shaped sixfold-symmetric structure, which is stabilized by a garland of six short tail fibers, running around the periphery of the dome. In the center of the dome, there is a membrane-puncturing device, containing three lysozyme domains, which disrupts the intermembrane peptidoglycan layer during infection.
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