Crystal Structure of the Carboxy-Terminal Region of the Bacteriophage T4 Proximal Long Tail Fiber Protein Gp34

Long tail fibers of bacteriophage T4 are formed by proteins gp34, gp35, gp36, and gp37, with gp34 located at the phage-proximal end and gp37 at the phage-distal, receptor-binding end. We have solved the structure of the carboxy-terminal region of gp34, consisting of amino acids 894-1289, by single-wavelength anomalous diffraction and extended the structure to amino acids 744-1289 using data collected from crystals containing longer gp34-fragments. The structure reveals three repeats of a mixed alpha-beta fibrous domain in residues 744 to 877. A triple-helical neck connects to an extended triple beta-helix domain (amino acids 900-1127) punctuated by two beta-prism domains. Next, a beta-prism domain decorated with short helices and extended beta-helices is present (residues 1146-1238), while the C-terminal end is capped with another short beta-helical region and three beta-hairpins. The structure provides insight into the stability of the fibrous gp34 protein.