Cylindrical crystals, contractile mechanisms of bacteriophages and the possible role of dislocations in contraction

Abstract

The tail sheath of T-even bacteriophages is an example of a cylindrical crystal. Contraction of the sheath involves changes in the crystal. It is shown that any change in a cylindrical crystal can be classified as one of 15 possible types of contraction. Several of the mechanisms that have been proposed for contraction of the phage tail sheath involve rather catastrophic changes in the sheath. A series of small waves of change, such as dislocations, passing through the crystal is suggested as the more likely process. The dislocation is introduced and the effect of its passage through a cylindrical crystal is analyzed. Some of the proposed contraction mechanisms are rationalized in terms of dislocations and it is shown that one particular mechanism involving dislocations passing through the tail sheath is compatible with available evidence. The possible role of dislocations in polymerized protein from tobacco mosaic virus is discussed. It is suggested that many biophysical processes of deformation and movement may depend on dislocations or dislocation-like waves of change.