A Structural Role for Dihydropteroyl Hexaglutamate in the Tail Baseplate of Various Bacteriophages

Abstract

A novel non-metabolic role is proposed for dihydropteroyl hexa-glutamate as a critical link binding together sub-structures of the tail of Escherichia coli bacteriophage T4. Six molecules of this folate compound have been found to be components of the complex tail baseplate of the phage particle. The baseplate is assembled using a total of at least 18 viral gene products in a series of reactions in which six wedge-like elements (each 0.7 × 10⁶ daltons) bind symmetrically around a central tail plug (1.55 × 10⁶ daltons) to form a flat hexagonal structure. It appears likely that the pteridine portion of the folate binds to a site on a viral-induced dihydro-folate reductase molecule, a wedge component, while the glutamate residues of the folate bind to a viral-induced thymidylate synthase molecule, a central plug component. Additionally, it appears that the folyl glutamate residues play a role in forming a flexible bond between the proximal end of the phage long tail fiber and the baseplate.