The K5 Lyase KflA Combines a Viral Tail Spike Structure with a Bacterial Polysaccharide Lyase Mechanism

James E Thompson,Meraj Pourhossein,Amy Waterhouse,Thomas Hudson,Marie Goldrick,Jeremy P Derrick,Ian S Roberts

doi:10.1074/jbc.m110.127571

James E Thompson, Meraj Pourhossein + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m110.127571

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Abstract

K5 lyase A (KflA) is a tail spike protein (TSP) encoded by a K5A coliphage, which cleaves K5 capsular polysaccharide, a glycosaminoglycan with the repeat unit [-4)-betaGlcA-(1,4)- alphaGlcNAc(1-], displayed on the surface of Escherichia coli K5 strains. The crystal structure of KflA reveals a trimeric arrangement, with each monomer containing a right-handed, single-stranded parallel beta-helix domain. Stable trimer formation by the intertwining of strands in the C-terminal domain, followed by proteolytic maturation, is likely to be catalyzed by an autochaperone as described for K1F endosialidase. The structure of KflA represents the first bacteriophage tail spike protein combining polysaccharide lyase activity with a single-stranded parallel beta-helix fold. We propose a catalytic site and mechanism representing convergence with the syn-beta-elimination site of heparinase II from Pedobacter heparinus.

Highlights

The structures of several bacterial glycosaminoglycan-degrading lyases have been published: hyaluronate lyases (EC 4.2.2.1) and chondroitin AC lyases (EC 4.2.2.5) have catalytic
Chondroitinase B (EC 4.2.2.4) from Pedobacter heparinus [16, 17] is the only glycosaminoglycan lyase known to contain the right-handed parallel ␤-helix topology that we report here for KflA
HylP1 contains a catalytic domain with triple-stranded ␤-helix topology (TS␤H),4 a fold previously observed in noncatalytic domains of other viral tail proteins, including bacteriophage T4 short tail fiber gp12 [19] and needle protein gp5 [20, 21]

Summary

The abbreviations used are

TS␤H, triple-stranded ␤-helix topology; TSP, tail spike protein; ␾, bacteriophage; gp, gene product. We report the structure of KflA, which represents the first viral tail spike protein with polysaccharide lyase activity and a catalytic single-stranded ␤-helix domain, a combination frequently observed in bacterial polysaccharide lyases. The proposed catalytic site resembles the syn-␤-elimination site of heparinase II, despite the fact that these enzymes have a very different topology

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