Long Noncontractile Tail Machines of Bacteriophages

Abstract

In this chapter, we describe the structure, assembly, function, and evolution of the long, noncontractile tail of the siphophages, which comprise ∼60% of the phages on earth. We place -particular emphasis on features that are conserved among all siphophages, and trace evolutionary connections between these phages and myophages, which possess long contractile tails. The large number of high-resolution structures of tail proteins solved recently coupled to studies of tail-related complexes by electron microscopy have provided many new insights in this area. In addition, the availability of thousands of phage and prophage genome sequences has allowed the delineation of several large families of tail proteins that were previously unrecognized. We also summarize current knowledge pertaining to the mechanisms by which siphophage tails recognize the bacterial cell surface and mediate DNA injection through the cell envelope. We show that phages infecting Gram-positive and Gram-negative bacteria possess distinct families of proteins at their tail tips that are involved in this process. Finally, we speculate on the evolutionary advantages provided by long phage tails.

Molecular architecture of tailed double-stranded DNA phages

“…12). 127,128 The tail of Myoviridae phages also contains a contractile sheath surrounding the tail tube. 128,129 The tail tip complex has different size and morphology in different phages.…”

“…The tail tip complex attaches the tape measure, or ruler, protein, which determines the length of the tail tube. 127,134,135 The tape measure protein is extended through the central channel of the tail tube as it is being built. The polymerizing tail tube protein molecules form a stack of hexameric rings on top of the tail tip complex, 136 which encircle the tape measure protein.…”

“…In Siphoviridae phages the tape measure protein may be involved in the creation of a channel for DNA translocation through the cell wall. 127 The tail tube protein The tail tube proteins usually do not polymerize until they encounter the tail tip complex. In solution these proteins typically contain many flexible loops, impeding the production of welldiffracting crystals.…”

Baseplate assembly of phage Mu: Defining the conserved core components of contractile-tailed phages and related bacterial systems

“…Upon contact with a host cell, the sheath contracts and drives the tail tube through the cell envelope and the genome is subsequently injected. Contractile tails are the most complex type of tail and are associated with phages bearing the largest genomes (1), suggesting that they may be the most powerful phage-genome delivery system. The remarkable capabilities of contractile phage tails are highlighted by the prevalence in bacteria of structures evolved from them, such as the type VI secretion system (T6SS) (2) and Photorhabdus virulence cassettes (PVCs) (3).…”

Bacteriophage SPP1 Tail Tube Protein Self-assembles into β-Structure-rich Tubes

“…In long-tailed phages, the main elementary unit of the genome delivery tube is the phage tail tube protein (TTP). 5 During assembly the tail adsorption apparatus is built first, thus providing a platform for helical polymerization of the TTP around a tape measure protein that defines the tail tube length (2,3). The tube is then tapered by tail completion proteins that build the interface for binding the viral capsid connector (4,5).…”