A model for fd phage penetration and assembly

Abstract

Below 15°C, chloroform causes fd phage to contract to I‐forms, which are compact structures about 1/3 as long as the original phage. Above 15°C, chloroform causes I‐forms to contract to even more compact spheroidal S‐forms. Here we show that the coat protein structure in I‐forms is the same as the protein structure in the phage and the protein structure in S‐forms is the same as the protein structure in bilayers. The conversions from fda˚I‐forms→S‐forms are therefore suggested to mimic steps in fd penetration. The same conversions, in reverse order, are suggested to mimic steps in fd assembly.

Conditionally and Transiently Disordered Proteins: Awakening Cryptic Disorder To Regulate Protein Function

“…The peculiarities of this process were analyzed in detail for the fd phage penetrating host cells. 195,196 Here, fd phage was shown to undergo large morphological changes, morphing first from the highly extended original form to the contracted I-form, about 1/3 as long as the original phage, then to the micelle-like spherical S-form, and finally to a helical form embedded in membrane bilayers. 196 Detailed biophysical analysis revealed that both I- and S-forms of the fd phage represented compact conformations characterized by nonrigid side chain packing and non-native morphologies but native-like secondary structures.…”