The Endosialidase Gene and Its Modular Architecture

Lyase Coliphage K5 Lyase Coliphage K1-5 Eliminase coli K5 strain 

It has been shown that the endosialidase is the only factor mediating Kl-specificity since the T7 phage lacking the endosialidase gene is unable to infect E. coli K1 strains. However, after enzymatic removal of the K1 capsule by endosialidase, the naked E. coli K1 strain can be infected by T7 [38]. Vice versa, the KIF phage is unable to infect E. coli strains lacking a polysialic acid capsule [108]. 

So far, five endosialidase genes have been cloned and expressed as functional proteins from . coli phages KIA, KIE, KIF, 63D, and Kl-5 [69-71, 78, 79]. The tailspike proteins endoNA, endoNE, and endoNKl-5 are equal in length (811 amino acids), whereas endoN63D and endoNF comprise 984, and 1,064 amino acids, respectively. EndoNE and endoNKl-5 are nearly identical with about 98% amino acid sequence similarity, and the recently published sequence of endoNA exhibits 90% similarity to endoNE. Therefore endoNE will be considered in the following as representative of this group. 

Endosialidases share a modular architecture (Fig. 1) which can be subdivided into three distinct parts  

The endosialidases differ in their N-terminal binding modules required for their attachment to the respective phage particle. EndoNF and endoN63D are N-terminally extended by 200 and 120 amino acids, respectively. These regions are a common feature of the tailspike or fiber proteins of most members of 

---