Function of bacteriophage G7C esterase tailspike in host cell adsorption

Abstract

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 show a great variability in their shapes, sizes, and location on the particle. Some RBPs are known to depolymerize surface polysaccharides of the host while others show no enzymatic activity. Here we report that both RBPs of podovirus G7C - tailspikes gp63.1 and gp66 - are essential for infection of its natural host bacterium E. coli 4s that populates the equine intestinal tract. We characterize the structure and function of gp63.1 and show that unlike any previously described RPB, gp63.1 deacetylates surface polysaccharides of E. coli 4s leaving the backbone of the polysaccharide intact. We demonstrate that 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 esterase domain of gp63.1 as well as domains mediating the gp63.1-gp66 interaction is widespread among all three families of tailed bacteriophages.

Not a barrier but a key: How bacteriophages exploit host's O‐antigen as an essential receptor to initiate infection

“…By contrast, the gp66 TSP C-terminus has an unrelated sequence for which the typical right-handed parallel b-helix depolymerase fold was predicted. Pulldown and mutation studies now showed that gp66 TSP is the branching point to bind a second TSP, gp63.1, to the tail (Prokhorov et al, 2017). The G7C gp63.1 TSP native trimer is a compactly folded fiber with the typical length of about 160 Å found in many bacteriophage O-antigen depolymerase TSP (Fig.…”

“…As shown for Salmonella podovirus P22 (Andres et al, 2010), also G7C needs an intact and fully functional TSP for successful infection. Oantigen chains in the G7C E. coli host show a narrow length distribution (Knirel et al, 2015;Prokhorov et al, 2017), stressing that this strain well controls its protective glycan layer. O-antigen specific bacteriophages in contrast have become experts in using this O-antigen for host cell invasion.…”

“…Evidence that enzymatic action on the glycan membrane receptor is a general theme in O-antigen specific bacteriophages now comes from new work focusing on TSP from the podovirus G7C in this issue of Molecular Microbiology (Prokhorov et al, 2017). G7C belongs to the subfamily of N4-like Enquartavirinae, unique in primarily injecting into their hosts a very large RNA polymerase prior to genome internalization (Kazmierczak and Rothman-Denes, 2006;Wittmann et al, 2015).…”

“…However, whereas highly purified protein-free LPS preparations are sufficient for particle opening (Andres et al, 2012), the additional role of membrane proteins tail to open the particle and initiate further steps for cell entry. Blue circles mark acetyl groups on O-antigen, red appendices in (B) represent a branching TSP structure to bind the deacetylase TSP as described for podovirus G7C in this issue of Molecular Microbiology (Prokhorov et al, 2017).…”

“… Structural models of the tailspike proteins (TSP) of (A) endorhamnosidase from Salmonella podovirus P22 (pdb: 2XC1) (Seul et al ., ), (B) gp63.1 from E. coli podovirus G7C (pdb: 4QNL) (Prokhorov et al ., ), (C) endosialidase from E. coli podovirus K1F (pdb:1V0E) (Stummeyer et al ., ), (D) endorhamnosidase from Salmonella myovirus Det7 (pdb:2V5I) (Walter et al ., ). The N‐terminal domains of Det7TSP and K1F have not been resolved in the X‐ray experiments and are thus missing from the presented structures.…”