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Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
Polysaccharide-Degrading Phages, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816506/9781555813079_Chap20-1.gif /docserver/preview/fulltext/10.1128/9781555816506/9781555813079_Chap20-2.gifAbstract:
This chapter discusses some of the recent developments and ideas and focuses on phages that possess virion-bound capsule depolymerization activities rather than those that simply bind to surface carbohydrate structures. The best-characterized polysaccharide-degrading phages are those that infect various strains of Escherichia coli. Polysaccharide-degrading phages were also isolated from other gram-negative bacteria, and in the case of Klebsiella, a tremendous amount of diversity was found. Probably the most structurally characterized extracellular polysaccharide-degrading phage tail protein is the lysogenic Salmonella P22 tailspike. The crystal structures of both the catalytic domain and the head-binding domain have been solved. P22, Sf6, and related phages are lysogenic, have very little biological or sequence relationship to the SP6 group, and based on their tail protein structures, may be categorized as their own distinct group. We may find that multispecific phages encoding more than one tail protein are fairly widespread. While much of this work can be done by the use of molecular techniques, phage typing is still a rapid and reliable method for identifying capsular antigens. In a recent study, a phage endosialidase (endo E) was used as an antibacterial to treat infections by E. coli 1 strains. Phages have long been known to play a role in bacterial pathogenesis by transducing virulence factors such as toxin genes.
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Penetration of bacteriophage K29 through the E. coli K29 capsule. Phage particles create a channel through the polysaccharide capsule to reach the cell surface. Reprinted from reference 9 with permission of the publisher.
Penetration of bacteriophage K29 through the E. coli K29 capsule. Phage particles create a channel through the polysaccharide capsule to reach the cell surface. Reprinted from reference 9 with permission of the publisher.
Electron immunomicroscopy of K1F particles. The incubation of phage with anti-endosialidase resulted in tail-to-tail lattices, indicating that the enzyme is part of the tail structure. Reprinted from reference 56 with permission.
Electron immunomicroscopy of K1F particles. The incubation of phage with anti-endosialidase resulted in tail-to-tail lattices, indicating that the enzyme is part of the tail structure. Reprinted from reference 56 with permission.
Modular genetic organization of the regions carrying the tail genes of members of the SP6 group of phages. In all four phages, these genes are located at one end of the ~40-kb dsDNA genome. Transcription of the tail genes of all four phages is probably initiated from a common SP6-like promoter. Immediately downstream, phages K1-5 and K5 encode a lyase, whereas SP6 encodes the P22-like endorhamnosidase and K1E has a small ORF of unknown function. In the second position downstream, K1-5 and K1E encode an endosialidase, whereas K5 and SP6 have unidentifiable ORFs.All four phages have a common 84- to 85-base intergenic region.
Modular genetic organization of the regions carrying the tail genes of members of the SP6 group of phages. In all four phages, these genes are located at one end of the ~40-kb dsDNA genome. Transcription of the tail genes of all four phages is probably initiated from a common SP6-like promoter. Immediately downstream, phages K1-5 and K5 encode a lyase, whereas SP6 encodes the P22-like endorhamnosidase and K1E has a small ORF of unknown function. In the second position downstream, K1-5 and K1E encode an endosialidase, whereas K5 and SP6 have unidentifiable ORFs.All four phages have a common 84- to 85-base intergenic region.
(A) Comparison of the tailspike proteins of phages P22 and SP6.The P22 tailspike has an N-terminal head-binding domain that is very similar to those of the tailspikes from phages HK620, Sf6, ST64T, and APSE-1.The SP6 tailspike lacks this domain but possesses a catalytic domain similar to that of P22. (B) The N terminus of the K1F endosialidase has similarity to the head-binding domain of the T7 tail fiber, which is missing from the K1-5 endosialidase.The C termini of both proteins are involved in folding proteins and are cleaved from the mature protein. Head attachment of the SP6 and K1-5 tailspikes may be mediated through a separate protein (see the text for further details).
(A) Comparison of the tailspike proteins of phages P22 and SP6.The P22 tailspike has an N-terminal head-binding domain that is very similar to those of the tailspikes from phages HK620, Sf6, ST64T, and APSE-1.The SP6 tailspike lacks this domain but possesses a catalytic domain similar to that of P22. (B) The N terminus of the K1F endosialidase has similarity to the head-binding domain of the T7 tail fiber, which is missing from the K1-5 endosialidase.The C termini of both proteins are involved in folding proteins and are cleaved from the mature protein. Head attachment of the SP6 and K1-5 tailspikes may be mediated through a separate protein (see the text for further details).