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NMR assignments for the insertion domain of bacteriophage Sf6 coat protein

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The P22 bacteriophage group is a subgroup of the λ phage supercluster, comprised of the three major sequence types Sf6, P22, and CUS-3, based on their capsid proteins. Our goal is to investigate the extent to which structure–function relationships are conserved for the viral coat proteins and I-domains in this subgroup. Sf6 is a phage that infects the human pathogen Shigella flexneri. The coat protein of Sf6 assembles into a procapsid, which further undergoes maturation during DNA packaging into an infectious virion. The Sf6 coat protein contains a genetically inserted domain, termed the I-domain, similar to the ones present in the P22 and CUS-3 coat proteins. Based on the P22 example, I-domains play important functional roles in capsid assembly, stability, viability, and size-determination. Here we report the 1H, 15N, and 13C chemical shift assignments for the I-domain of the Sf6 phage coat protein. Chemical shift-based secondary structure prediction and hydrogen-bond patterns from a long-range HNCO experiment indicate that the Sf6 I-domain adopts a 6-stranded β-barrel fold like those of P22 and CUS-3 but with important differences, including the absence of the D-loop that is critical for capsid assembly and the addition of a novel disordered loop region.

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We thank Dr. Mark Maciejewski for help in setting up NMR experiments, Anne R. Kaplan for help in data processing and analysis, and Drs. A.D. Schuyler, M.R. Gryk, and J.C. Hoch for use of the computational platform NMRbox ( This work was supported by NIH Grant R01 GM076661.

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Correspondence to Carolyn M. Teschke or Andrei T. Alexandrescu.

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All experiments complied with all laws of the United States of America.

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The authors declare no conflict of interest.

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Tripler, T.N., Teschke, C.M. & Alexandrescu, A.T. NMR assignments for the insertion domain of bacteriophage Sf6 coat protein. Biomol NMR Assign 11, 35–38 (2017).

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  • Structure homology
  • Protein dynamics
  • Intrinsically disordered proteins
  • Icosahedral particles
  • Conserved folding motifs