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ORF334 in Vibrio Phage KVP40 Plays the Role of gp27 in T4 Phage To Form a Heterohexameric Complex

Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4359-B39 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan,¹ National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 2, Umezono 1-1-4, Tsukuba Science City, Ibaraki 305-8568, Japan²

Received 18 January 2008/ Accepted 28 February 2008

KVP40 is a T4-related phage, composed of 386 open reading frames (ORFs), that has a broad host range. Here, we overexpressed, purified, and biophysically characterized two of the proteins encoded in the KVP40 genome, namely, gp5 and ORF334. Homology-based comparison between KVP40 and its better-characterized sister phage, T4, was used to estimate the two KVP40 proteins' functions. KVP40 gp5 shared significant homology with T4 gp5 in the N- and C-terminal domains. Unlike T4 gp5, KVP40 gp5 lacked the internal lysozyme domain. Like T4 gp5, KVP40 gp5 was found to form a homotrimer in solution. In stark contrast, KVP40 ORF334 shared no significant homology with any known proteins from T4-related phages. KVP40 ORF334 was found to form a heterohexamer with KVP40 gp5 in solution in a fashion nearly identical to the interaction between the T4 gp5 and gp27 proteins. Electron microscope image analysis of the KVP40 gp5-ORF334 complex indicated that it had dimensions very similar to those of the T4 gp5-gp27 structure. On the basis of our biophysical characterization, along with positional genome information, we propose that ORF334 is the ortholog of T4 gp27 and that it plays the role of a linker between gp5 and the phage baseplate.

Published ahead of print on 7 March 2008.