Bacteriophages recognize and bind to their hosts with the help of receptor-binding proteins (RBPs) that emanate from the phage particle in the form of fibers or tailspikes. RBPs of podovirus G7C tailspikes gp63.1 and gp66 are essential for infection of its natural host bacterium E. coli 4s. Gp63.1 and gp66 form a stable complex, in which the N-terminal part of gp66 serves as an attachment site for gp63.1 and anchors the gp63.1-gp66 complex to the G7C tail. The two N-terminal domains show 70% sequence identity to the N-terminal region of the CBA120 phage tailspike 1 (orf210, TSP1) [1]. The N-terminal domain of TSP1 is the virion head binding domain that interfaces with the phage baseplate. The N-terminal domain can be further divided into two subdomains, each beginning with a alpha-helix followed by an anti-parallel beta-sandwich. Subdomain two folds similarly to the chitin binding domain of Chitinase from Bacillus circulans [2].

1: Function of bacteriophage G7C esterase tailspike in host cell adsorption. Prokhorov NS, Riccio C, Zdorovenko EL, Shneider MM, Browning C, Knirel YA, Leiman PG, Letarov AV; Mol Microbiol. 2017;105:385-398. PMID:28513100

2: Crystal structure of ORF210 from E. coli O157:H1 phage CBA120 (TSP1), a putative tailspike protein. Chen C, Bales P, Greenfield J, Heselpoth RD, Nelson DC, Herzberg O; PLoS One. 2014;9:e93156. PMID:24671238