Because of the large size and simple linear structure of the assembled tail fiber, crystallizing whole tail fibers has proved challenging, although some fragments of tail fiber proteins have been assembled, crystallized, and their structures solved. In this review, we discuss what is known about the detailed structure and function of the different long tail fiber domains. Partial crystal structures of gp34 and gp37 have revealed the presence of new protein folds, some of which are present in several repeats, while others are apparently unique. This information is critically needed to engineer machines with novel host. Caudovirales (tailed bacterial viruses) usually have fibers attached to the distal end of their tail. The pathway of fibers assembly has been well studied in bacteriophage T4. Also includes the type VI secretion system, R-type pyocins, the antifeeding prophage/Photorhabdus virulence cassette and other tailocins.
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