Structural component of the distal-half of the long-tail fiber. It constitutes the part of the long-tail fibers that recognizes the bacterial receptor. The long-tail fiber of T4 is about 1600 Angstroms long with a kink in the middle that divides the fiber into proximal and distal halves. The thin tip of the distal half-fiber interacts with the bacterial lipopolysaccharide receptor and specifies the host range of the phage. The long-tail fibers are trimeric, with a stoichiometry of gp34/gp37/gp36/gp35 of 3:3:3:1. The two gp37 protein chains run in parallel, the length of the distal half-fiber, with the amino end near the center kink of the fiber and the carboxyl end at the distal tip. The other polypeptides are distributed uniformly along the length of the distal half-fiber. Belongs to the tail fiber family.