Bacteriophage tail proteins

A recently discovered subset of triple-stranded /l-helices from bacteriophage tail proteins (alternatively termed triple-stranded /1-solenoids ) represents another distinct group of /1-fibrous folds (Fig. 3B). In these structures, three identical chains related by threefold rotational symmetry wind around a common axis. These chains form unusual parallel /1-sheets with no intra- and only intermolecular -structural hydrogen bonding. Kajava and Steven (this volume) survey the distinguishing structural features of the known triple-stranded /1-solenoids, also documenting their notable diversity and differences in comparison to the single-stranded /1-solenoids. 

All the above-mentioned proteins have single-stranded folds based on solenoidal windings of one polypeptide chain. Recently, however, several triple-stranded /1-helices (alternatively, triple-stranded /l-solenoids ) have been described in bacteriophage tail proteins (Kanamaru et al., 2002 Smith et al., 2005 Stummeyer et al., 2005 van Raaij et al, 2001). In these structures, three identical chains wind around a common axis and their coils have an axial rise of 14.5 A, that is, 3 x 4.83 A (for details see Sections IV and V.D). In this chapter, triple-stranded /l-solenoids will be abbreviated as TS /l-solenoids, while the term /1-solenoid, if not otherwise qualified, will apply to the predominant group of single-stranded /l-solenoids. 

Bacteriophage T7 Bacteriophage T7 and its close relative T3 are relatively small DNA viruses that infect Escherichia coli. (Some strains of Shigella and Pasteurella are also hosts for phage T7.) The virus particle has an icosahedral head and a very small tail. The virus particle is fairly complex, with S different proteins in the head and 3-6 different proteins in the tail. One tail protein, the tail fiber protein, is the means by which the virus particle attaches to the bacterial cell surface. Only female cells of Escherichia coli can be infected with T7 male cells can be infected but the multiplication process is terminated during the latent period. 

Another remarkable example is extension of the acrosomal process from a sperm cell of the horseshoe crab Limulus polyphemus at fertilization. A bundle of actin filaments in a crystalline state lies coiled around the base of the nucleus. At fertilization the bundle uncoils and slides through a tunnel in the nucleus to form a 60 pm-long acrosomal process within a few seconds. The uncoiled bundle is also crystalline. The coiled bundle is apparently overtwisted and an actin crosslinking protein scrum mediates the conformational alteration that takes place.339 A somewhat related process maybe involved in contraction of bacteriophage tails (pp. 363,364)... 

FIGURE 16.5 Lytic cycle of bacteriophage X. D decoration protein pV tail protein V. 

FIGURE 17.4 Bacteriophage lambda. D, decoration protein V, tail protein cos, cohesive ends. 

Katsura I, Structure and function of the major tail protein of bacteriophage lambda, Mutants having small major tail protein molecules in their virion, J. Mol. Biol., 146 493-512, 1981. 

Fig. 1. Schematic drawings of the viruses discussed in this chapter. (A) An icosahe-dral virus with fiber proteins inserted in its pentameric vertices. The gray box denotes domains with known structures for adenovirus, reovirus, and bacteriophage PRD1, in each case containing the head domain and proximal part of the triple /8-spiral shaft domain. (B) Contractile-tailed bacteriophage T4. T4 contains three different fibrous proteins, fibritin connected to the neck, the long (bent) fibers connected to the base plate, and the short fibers also connected to the base plate. Only two of each of the trimeric fibrous proteins are shown for clarity. The gray box denotes domains with known structure for the T4 short fiber.

The T4 short tail fiber triple /l-helix is connected to a more globular head domain via residues 333-341, which form a very short a-helical triple coiled-coil. Residues 342-396, together with the C-terminal /1-strand composed of amino acids 518-527 (the collar ), are the only part of the structure in which the monomer has a recognizable fold. It may therefore be the first part of the protein to fold, followed by a zipping-up of the N-terminal domain and the top domain. The small, globular, domain contains six /1-strands and one a-helix and has some structural homology to gpl 1, also of bacteriophage T4. Three of the /1-strands and the a-helix formed by residues... 

Wang,J., Hofnung, M., and Charbit, A. (2000). The C-terminal portion of the tail fiber protein of bacteriophage lambda is responsible for binding to LamB, its receptor at the surface of Escherichia coli K-12./. Bacteriol. 182, 508-512. 

Many other oligomeric enzymes and other complex assemblies of more than one kind of protein subunit are known. For example, the 2-oxoacid dehydrogenases are huge 2000- to 4000-kDa complexes containing three different proteins with different enzymatic activities in a cubic array (Fig. 15-14). The filaments of striated muscle (Chapter 19), antibodies and complement of blood (Chapter 31), and the tailed bacteriophages (Box 7-C ) all have complex molecular architectures. 

Figure 7-29 Assembly sequence for bacteriophage T4 with details for the tail. The numbers refer to the genes in the T4 chromosome map (Fig. 26-2). A "P" after the number indicates that the protein gene product is incorporated into the phage tail. Other numbers indicate gene products that are thought to have essential catalytic functions in the assembly process. Adapted from King and Mykolajewycz236 and Kikuchi and King.214...

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