Characterization of the helper proteins for the assembly of tail fibers of coliphages T4 and lambda

Abstract

Assembly of tail fibers of coliphage T4 requires the action of helper proteins. In the absence of one of these, protein 38 (p38), p37, constituting the distal part of the long tail fiber, fails to oligomerize. In the absence of the other, p57, p34 (another component of the long tail fiber), p37, and p12 (the subunit of the short tail fiber) remain unassembled. p38 can be replaced by the Tfa (tail fiber assembly) protein (pTfa) of phage , which has the advantage of remaining soluble even when produced in massive amounts. The mechanisms of action of the helpers are unknown. As a first step towards elucidation of these mechanisms, p57 and pTfa have been purified to homogeneity and have been crystallized. The identity of gene 57 (g57), not known with certainty previously, has been established. The 79-residue protein p57 represents a very exotic polypeptide. It is oligomeric and acidic (an excess of nine negative charges). It does not contain Phe, Trp, Tyr, His, Pro, and Cys. Only 25 N-terminal residues were still able to complement a g57 amber mutant, although with a reduced efficiency. In cells overproducing the protein, it assumed a quasi-crystalline structure in the form of highly ordered fibers. They traversed the cells longitudinally (and thus blocked cell division) with a diameter approaching that of the cell and with a hexagonal appearance. The 194-residue pTfa is also acidic (an excess of 13 negative charges) and is likely to be dimeric.Receptors at the bacterial cell surface are recognized by phage T4 with the free ends of its long tail fibers (1, 26, 51). These fibers consist of four proteins: p34, p35, p36, and p37. p37 constitutes the distal part of the fiber and mediates receptor recognition (2, 51) with an area near its C terminus (17, 32). p34, p36, and p37 in these tail fibers are oligomers. It had earlier been assumed that they form dimers (50, 53); most likely, however, they are trimers. There is experimental evidence for the trimeric state of p34 and p37 (8), and regarding p37, strong indirect evidence stems from the fact that the tail fibers of phage T7 consist of trimers of this virion's p17 (49). Tail fiber genes are of a mosaic structure (summarized in reference 16), very strongly indicating horizontal transfer of gene fragments. Corresponding protein fragments, partially identical to sequences of p17, exist in p37 of phages K3 and T2 (16), which are very closely related to T4. There is little doubt, therefore that all p37 proteins are trimeric. Assembly of these fibers requires helpers (for a recent review, see reference 54), which are absent from the mature virion. In the absence of one of these, p38, p37 fails to oligomerize. A gene 38 (g38) partial bypass mutant has been isolated (3), and it has been shown to consist of a duplication of residues 797 to 805 (17) of the 1,026-residue p37 (36). This is the area where p38 is believed to act on p37 (48). Infection with the mutant phage leads to about 30% assembled distal half-fibers (compared with the amount produced in wild-type phage infectio...

Genome of Bacteriophage P1

“…In contrast to T4 gp38, the Tfa protein of Ur-is a virion component (133). Although there is little homology between the two, each can replace the chaperone function of the other (117,226). This function of Tfa does not require virion attachment.…”

Bacteriophage T4 Genome

“…In the established model (531), gp51 is involved in the hub assembly while gp57A is involved in assembly of both the short and long tail fibers. gp57A consists of 79 aa, and more than 90% is ␣-helix (391,699). Although the molecular nature of the protein has been worked out, the interactions with the short and long tail fibers are unknown.…”

Crystallization of the carboxy-terminal region of the bacteriophage T4 proximal long tail fibre protein gp34

“…The gp36 protein subunit is located at the proximal end of the distal half-fibre, while gp37 makes up the rest of the shin, including the very distal receptor-recognizing tip or foot (Bartual, Otero et al, 2010). The gp12, gp34 and gp37 trimers need the chaperone gp57A to help them fold correctly (Hashemolhosseini et al, 1996;Ali et al, 2003). By co-expression with gp57A, we have produced carboxy-terminal fragments of the proximal tail fibre protein gp34 and crystallized them.…”