Page about T4 Phage

Tail with fibres: "The T4 tail and fibres are important tools for bacteriophage interactions with its host. This part of the capsid determines phage specificity and enables the infecting of bacteria. The tail is composed of two concentric protein cylinders. The outer cylinder is contractile and the inner one builds the channel for the nucleic acid that is stored in the head. Such a syringe-like construction of the tail enables the injection of DNA into the bacterial cell. The inner tube has a 90-Ǻ outer and 40-Ǻ inner diameter and is constructed of 144 copies of gp19 (Table 2). The outer part of the tail is called the tail sheath. It is built by 144 copies of gp18 (in accordance with the number of gp19). The length of the tail is probably determined by the "ruler protein" (or template) gp29 (Leiman et al. 2003). The uncontracted tail is 1000 Ǻ long and 210 Ǻ in diameter (Mesyanshinov et al. 2004), which corresponds to the dimensions of the tail sheath. When contracted, the tail sheath is only 360 Ǻ long and 270 Ǻ wide. The length of the tail tube does not change during contraction (Leiman et al. 2003). At either end of the cylinders are the baseplate and fibres. The baseplate is a multiprotein structure 270Ĺ high and 520 Ĺ in diameter at its widest part. The proteins form six wedges surrounding the central hub with the help of two trimeric proteins, (gp9)₃ and (gp12)₃. Gp11, gp10, gp7, gp8, gp6, gp53, and gp25 combine sequentially to build up the wedges. Gp5, gp27, gp29, and probably gp26 and gp28 form the baseplate's hub (Leiman et al. 2003). Gp5 has a lysozyme domain which is necessary for the digestion of the bacterial peptidoglycan layer during the infection process.

One of bacteriophage T4's most useful device are the fibres: long tail fibres (LTFs) and short tail fibres (STFs) located on the distal part of the tail and whiskers extending outwardly from the collar region of the virion (Conley and Wood 1975). The long tail fibres, which are responsible for the recognition of specific receptors on the bacteria's surface, are ~1450 Ĺ long and ~40 Ĺ in diameter (Leiman et al. 2003). Each fibre consists of two halves: the proximal half encoded by gene 34 and the distal encoded by genes 36 and 37. These halves are connected by gp35, which interacts with gp34 and gp36. The protein connecting the LTFs with the baseplate is gp9. Association of the proximal part of the fibre with gp9 is assisted by gp63. gp9 has an extremely important role during infection. After the binding of an LTF to the LPS (lipopolysaccharide) on the bacteria's wall, it initiates the transition of the baseplate structure into a star-like conformation and the tail sheath contraction that enables injection of the phage's DNA into the cell. Besides that, gp9 is also responsible for the collective movements of the fibres and for preventing the baseplate from abortive triggering. The short tail fibres are gp12 trimers attached to the baseplate by gp11. They are 340-Ĺ-long club-like structures with a narrowing in the middle where the fibre can bend up to 90ş. STFs are responsible for binding the phage particle to the bacteria's surface. During the infection process the C-termini of gp12 molecule bind to the core region of the LPS cell-surface receptor (Mesyanzhinov et al. 2004).