Head-Tail Connector Protein gp6 of Bacteriophage HK97 and similar proteins
The bacteriophage HK97 gp6 protein is critical in the assembly of the connector, a specialized structure that serves as an interface for head and tail attachment, as well as a point at which DNA exits the head during infection by the bacteriophage. It forms a dodecameric ring structure that comprises the middle ring of the connector, located between the portal protein (attached to the head) and the gp7 ring (attached to the tail). It is a component of the mature phage and the absence of HK97 gp6 results in defective head-tail joining and the absence of mature phage particles. Although the crystal structure of HK97 gp6 shows an unexpected 13-mer ring, the biological form present in the mature phage is believed to be a dodecamer.