Bacteriophage T4 long tail fiber domains

Abstract

Bacteriophage T4 initially recognizes its host cells using its long tail fibers. Long tail fibers consist of a phage-proximal and a phage-distal rod, each around 80 nm long and attached to each other at a slight angle. The phage-proximal rod is formed by a homo-trimer of gene product 34 (gp34) and is attached to the phage-distal rod by a monomer of gp35. The phage-distal rod consists of two protein trimers: a trimer of gp36, attached to gp35, although most of the phage-distal rod, including the receptor-binding domain, is formed by a trimer of gp37. In this review, we discuss what is known about the detailed structure and function of the different long tail fiber domains. Partial crystal structures of gp34 and gp37 have revealed the presence of new protein folds, some of which are present in several repeats, while others are apparently unique. Gp38, a phage chaperone protein necessary for folding of gp37, is thought to act on an α-helical coiled-coil region in gp37. Future studies should reveal the remaining structure of the long tail fibers, how they assemble into a functional unit, and how the long tail fibers trigger the infection process after successful recognition of a suitable host bacterium.

Keywords: Assembly; Bacteriophage T4; Long tail fiber; Protein folds; α-Helical coiled-coil; β-Structure.

Fig. 1

Domainal organization of the bacteriophage T4 long tail fiber. a Outline of the bacteriophage T4 long tail fiber (LTF), composed of gene products (gp)34–gp37. The proximal tail fiber is on the left and the distal tail fiber is on the right, as in the marked tail fiber in the whole phage drawing. Lines indicate approximate borders between the four proteins. b Domainal and protein functional correspondence for the LTF. Protein locations are indicated above the outline and the functional domains are indicated under the outline. Mass domain names are shown for the proximal half-fiber (P1–P5), the knee-cap (KC), and the distal half-fiber (D1–D11), and refer to the mass domains identified by Cerritelli et al. (1996). The correspondence between the functional and mass domains as well as the position of the mass domains is approximate. c Detailed positions of functional domains, with the numbers after each function description indicating the amino acid (aa) residues in that protein for that domain when known. Amino (N) and carboxy (C) ends of gp34, gp36, and gp37 are indicated. There is no corresponding information for gp35. The two deletions mentioned in the text in the central rod region of gp37 are also shown

Fig. 2

Structure of the phage T4 LTF tip. a Side view of a ribbon representation of the gp37 trimer fragment containing the D10 and D11 domains. The three chains of the protein homo-trimer are in green, red, and blue, respectively. The iron ions are shown as orange balls, and the histidine side chains coordinating them are visualized. Residues forming the approximate domain boundaries are labeled. b End-on view of the receptor-binding head domain in which the interweaving of the three chains is clearly visible. Molecular graphics images were produced using the UCSF Chimera package from the Resource for Biocomputing, Visualization, and Informatics at the University of California, San Francisco (supported by NIH P41 RR-01081) (Pettersen et al. 2004)

Fig. 3

Alignment of the first 60 amino acids of gp37 with other bacteriophage equivalent proteins as identified by BLAST-P. Asterisks indicate positions that are identical in all sequences, black highlighting indicates the amino acid that is present in ≥50% of the sequences, gray highlighting indicates conserved substitutions in >50% of the sequences (Henikoff and Henikoff ; Riek et al. 2007)

Fig. 4

Structure of the proximal rod of the phage T4 LTF. Side view of a ribbon representation of the gp34 fragment containing part of the P2 and the whole P3, P4, and P5 domains. The three chains of the protein homo-trimer are in green, red, and blue. Residues mentioned in the text are labeled