Filamentous phage studied by magic-angle spinning NMR: Resonance assignment and secondary structure of the coat protein in Pf1

Assignments are presented for resonances in the magic-angle spinning solid-state NMR spectra of the major coat protein subunit of the filamentous bacteriophage Pf1. NMR spectra were collected on uniformly ¹³C and ¹⁵N isotopically enriched, polyethylene glycol precipitated samples of fully infectious and hydrated phage. Site-specific assignments were achieved for 231 of the 251 labeled atoms (92%) of the 46-residue-long coat protein, including 136 of the 138 backbone atoms, by means of two- and three-dimensional ¹⁵N and ¹³C correlation experiments. A single chemical shift was observed for the vast majority of atoms, suggesting a single conformation for the 7300 subunits in the 36 MDa virion in its high-temperature form. On the other hand, multiple chemical shifts were observed for the Cα, Cβ, and Cγ atoms of T5 in the helix terminus and the Cα and Cβ atoms of M42 in the DNA interaction domain. The chemical shifts of the backbone atoms indicate that the coat protein conformation involves a 40-residue continuous α-helix extending from residue 6 to the C-terminus.