Structure of the bacteriophage T4 long tail fiber needle-shaped receptor-binding tip

Abstract

Bacteriophages are the most numerous organisms in the biosphere. They are exploited in an emergent array of applications including bactericidal and experimental phage therapy applications. In spite of their biological significance and the spectrum of potential applications, little high-resolution structural detail is available on their receptor-binding fibres. Here we present the crystal structure of the receptor-binding tip (D10 plus D11, Fig. 1) of the bacteriophage T4 long tail fibre, which is highly homologous to the tip of the bacteriophage lambda side tail fibres. It reveals an unusual elongated six-stranded anti-parallel beta-strand needle domain containing seven iron ions coordinated by histidine residues arranged co-linearly along the core of the biological unit (Fig. 2). At the end of the tip the three chains intertwine forming a broader head domain, which contains the putative receptor interaction site. The structure reveals a previously unknown beta-structured fibrous fold, explains the remarkable stability of the fibre and provides a framework for mutations to expand or modulate receptor-binding specificity.