Subunit Orientation in the Filamentous Virus Ff(fd, f1, M13)

Abstract

The Fffilamentous viruses ( fd, M13, f1) are important models for membrane protein assembly and are used extensively as cloning vectors and vehicles for peptide display. The thread-like virion (∼6 nm × 880 nm) comprises a single-stranded DNA genome sheathed by ∼2700 copies of a 50-residue α-helical subunit (pVIII). The average inclination of pVIII subunits from the virion axis has been determined experimentally by polarized Raman microspectroscopy of oriented fdfibers, using the amide I Raman tensors obtained from a peptide single crystal. It is found that the average tilt angle, τ, between the pVIII α-helix and the virion axis falls within the range 13 < τ < 20°.