Structural basis of virion assembly in the Mycobacterium tuberculosis-infecting mycobacteriophage SWU1

Single-particle cryo-EM resolved essentially the entire Mycobacteriophage SWU1 virion architecture, including four modules at 3.22–3.70 Å resolution, revealing a T=7 capsid and a unique baseplate geometry.

• Why it matters: Drug-resistant tuberculosis renews interest in bacteriophage therapy, but rational engineering needs atomic-level virion architecture to guide optimization.
• What they did: The study used localized reconstruction of four SWU1 modules—capsid, portal vertex, tail, and baseplate—by cryo-EM, achieving 3.62 Å, 3.51 Å, 3.70 Å, and 3.22 Å resolutions.
• The result: The T=7 capsid contains 415 copies of an HK97-fold major capsid protein and no decoration protein in density, while the 12-fold portal and symmetry-free baseplate reconstruction define non-equivalent contacts and a geometry without precedent.

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