Crystallographic studies on host-interacting proteins of phage K virion

Antonio Pichel Beleiro, Department of Biological Sciences, Cork Institute of Technology, Cork, Ireland


Phage K is a lytic bacteriophage that infects a broad range of staphylococci, including some methicillin-resistant Staphylococcus aureus strains. Phage K attaches to its host via a baseplate. The contracted conformation of the baseplate contains a fiber and two receptorbinding proteins responsible for the interaction with the host. The native conformation of the baseplate also includes a tail central spike that shears off after contraction. The aim of the thesis is the structural characterization of phage K receptor-binding proteins and tail central spike. Experimentally, the thesis relies on crystallographic methods, which encompass: production of suitable sample, crystallization, diffraction, and data processing. Phage K has two receptor-binding proteins: gp146 and gp144. Both receptor-binding proteins are β-structure homotrimers organized in four trimeric modules. Trimeric modules I, II, and III are mixed β-sheets that form the “shaft” of the structures. The tip (domain IV) is an antiparallel β-sandwich with topological differences between the apical regions of the gp146 and gp144 domains. Gp146 has an additional peripheral domain with a galectin-like folding. The crystal structure of gp144 can be fitted in the fiber of the contracted baseplate. The location of gp146 in the baseplate is uncertain. Functionally, gp146 and gp144 interact with wall teichoic acid. In the galectin-like domain of gp146, a binding site was identified by co-crystallization with a synthetic analog of the wall teichoic acid. Additionally, the co-crystallization with rac-glycerol 1-phosphate suggests three possible binding sites in gp146 and one in gp144. Phage K tail central spike is gp155. The carboxy-terminal domain of gp155 is a glycerophosphodiester phosphodiesterase. Gp155 carboxy-terminal domain is very similar to bacterial phosphodiester phosphodiesterases; it consists of a TIM-barrel and an insertion domain. The active site of gp155 carboxy-terminal domain has two pH-dependent conformations that resemble the conformations of bacterial phosphodiester phosphodiesterases.