Cryo-EM Reveals Structural Diversity in Prolate-headed Mycobacteriophage Mycofy1.

Mycobacteriophages show promise in treating antibiotic-resistant mycobacterial infections. Here, we isolated Mycofy1, a mycobacteriophage, using M. smegmatis as a host. Cryo-EM analysis revealed that Mycofy1 possesses a prolate head and a long non-contractile tail. We determined structures of its head, head-to-tail interface, terminator, and tail tube to resolutions of ∼3.5 Å. Unexpectedly, we identified two distinct types of prolate head structures, exhibiting a 36° relative rotation in the top cap region. Additionally, the head-to-tail interface demonstrated flexibility. Our structures provide high-resolution cryo-EM data of a mycobacteriophage with a prolate head, as well as detailed structural information of the head-to-tail interface and head-proximal tail region in this phage group. These findings advance our understanding of assembly mechanisms in tailed bacteriophages.