Phage tail fibre assembly proteins employ a modular structure to drive the correct folding of diverse fibres


Phage tail fibres are elongated protein assemblies capable of specific recognition of bacterial surfaces during the first step of viral infection1,2,3,4. The folding of these complex trimeric structures often requires a phage-encoded tail fibre assembly (Tfa) protein5,6,7. Despite the wide occurrence of Tfa proteins, their functional mechanism has not been elucidated. Here, we investigate the tail fibre and Tfa of Escherichia coli phage Mu. We demonstrate that Tfa forms a stable complex with the tail fibre, and present a 2.1 Å resolution X-ray crystal structure of this complex. We find that Tfa proteins are comprised of two domains: a non-conserved N-terminal domain that binds to the C-terminal region of the fibre and a conserved C-terminal domain that probably mediates fibre oligomerization and assembly. Tfa forms rapidly exchanging multimers on its own, but not a stable trimer, implying that Tfa does not specify the trimeric state of the fibre. We propose that the key conserved role of Tfa is to ensure that fibre assembly and multimerization initiates at the C terminus, ensuring that the intertwined and repetitive structural elements of fibres come together in the correct sequence. The universal importance of correctly aligning the C termini of phage fibres is highlighted by our work.

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Fig. 1: TfaMu forms a stable complex with the fibre.
Fig. 2: Structure of the TfibMu:TfaMu complex.
Fig. 3: TfaMu is a two-domain protein that forms a functional complex with the C-terminal region of TfibMu and is present in the mature phage particles.
Fig. 4: Two-domain architecture of TfaMu.

Data availability

The authors declare that the data supporting the findings of this study are available within the paper and the Supplementary Information, or from the corresponding authors upon request. The structure of the TfibMu:TfaMu complex obtained in the current study is available in the PDB with the following accession code: PDB ID 5YVQ.


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This work was supported by funding from the Canadian Institutes of Health Research to A.R.D. (Operating grant MOP-115039 and Foundation grant FDN-15427). S.T. was supported by a grant from Gunma University Medical Innovation Project and in part by the Cooperative Research Program of the Institute for Protein Research, Osaka University, CR-18-54. Diffraction data were collected at the Osaka University beamline BL44XU at SPring-8, Japan (Proposal nos. 2013B6500, 2014A6500 and 2014B6500). We thank P. Leiman and K. Maxwell for useful discussions of the manuscript.

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O.I.N. designed experiments, performed bioinformatic analysis, performed experiments, analysed data and wrote the manuscript. K.S. purified and obtained crystals of the TfibMu:TfaMu complex. S.T. supervised these experiments and helped in writing the manuscript. E.Y. and A.N. determined the TfibMu:TfaMu complex structure; T.I. performed the final refinement of the structure. C.R.B. obtained liquid chromatography–tandem mass spectrometry results of CsCl-purified wild-type phage Mu and created baseplate wedge constructs. A.R.D. supervised experiments and wrote the manuscript.

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Correspondence to Shigeki Takeda or Alan R. Davidson.

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North, O.I., Sakai, K., Yamashita, E. et al. Phage tail fibre assembly proteins employ a modular structure to drive the correct folding of diverse fibres. Nat Microbiol 4, 1645–1653 (2019).

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