Ubiquitous Carbohydrate Binding Modules Decorate 936 Lactococcal Siphophage Virions

Stephen Hayes,Arjen Nauta,Douwe Van Sinderen,Christian Cambillau,Jennifer Mahony,Renaud Vincentelli,Laurie Ramond

doi:10.3390/v11070631

Abstract

With the availability of an increasing number of 3D structures of bacteriophage components, combined with powerful in silico predictive tools, it has become possible to decipher the structural assembly and functionality of phage adhesion devices. In the current study, we examined 113 members of the 936 group of lactococcal siphophages, and identified a number of Carbohydrate Binding Modules (CBMs) in the neck passage structure and major tail protein, on top of evolved Dit proteins, as recently reported by us. The binding ability of such CBM-containing proteins was assessed through the construction of green fluorescent protein fusion proteins and subsequent binding assays. Two CBMs, one from the phage tail and another from the neck, demonstrated definite binding to their phage-specific host. Bioinformatic analysis of the structural proteins of 936 phages reveals that they incorporate binding modules which exhibit structural homology to those found in other lactococcal phage groups and beyond, indicating that phages utilize common structural “bricks” to enhance host binding capabilities. The omnipresence of CBMs in Siphophages supports their beneficial role in the infection process, as they can be combined in various ways to form appendages with different shapes and functionalities, ensuring their success in host detection in their respective ecological niches.

Highlights

Bacteriophages of Lactococcus lactis are well known to cause fermentation disruptions and product inconsistencies with a consequent economic cost to the dairy industry [1], which in turn has fuelled intense scientific scrutiny of such phage groups [2]
The structure of the entire virion of the 936 phage p2 has been resolved by electron microscopy (EM) [32], while the Receptor Binding Protein (RBP) structures of phages p2 and bIL170 have been determined by X-ray crystallography [5,10,12], providing a highly useful resource for the analysis of structural components of these phages
The results indicate that the tail protein extension (TpeX) Carbohydrate Binding Modules (CBMs) domain binds to all infection positive hosts, and to none of the non-host strains, exhibiting host-specific binding

Summary

Introduction

Bacteriophages (or phages) of Lactococcus lactis are well known to cause fermentation disruptions and product inconsistencies with a consequent economic cost to the dairy industry [1], which in turn has fuelled intense scientific scrutiny of such phage groups [2]. Chief among the most commonly encountered lactococcal phages are those belonging to the lytic 936 group [3], for which 164 complete genome sequences are publicly available (NCBI Database). The availability of such a large number of phage-group specific genome sequences is rather unique, and renders the 936 group an ideal model group for the study of phage–host interactions. An initial, yet crucial step in the phage infection process is the specific recognition of, and binding to the bacterial host. Tailed phages of the order Caudovirales, including the lactococcal 936 group phages, recognize and bind to their host utilizing a complex adhesion device at the distal end of their tail, which.

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