Structure of normal and contracted tail sheaths of T4 bacteriophage

The structural arrangement of protein subunits in extended and contracted tail sheaths of T4 bacteriophage has been studied by optical diffractometry of electron micrographs. The analysis of such diffraction patterns shows that the extended sheath consists of annuli of six subunits, these being arranged in a helix of close to seven annuli in two turns. The annulus repeat in the helix direction is 38[middle dot]1 A. For the contracted sheath the axial periodicity is found to be 32 A, which must arise from twice the repeat of the extended sheath. The symmetry of the contracted sheath diffraction pattern is consistent with a helix of five annuli (of 12 subunits) in one turn. Such a structure is seen to arise simply from the extended sheath by the merging of pairs of annuli. The dimensional changes suggested by the above structures indicate that contraction is accompanied by a conformational change in the subunit. The pairing of annuli may have to be a progressive one in order not to isolate single annuli, thus being an example of what could be called a "domino reaction".Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33307/1/0000701.pd

Conformational Dynamics of Actin: Effectors and Implications for Biological Function

Actin is a protein abundant in many cell types. Decades of investigations have provided evidence that it has many functions in living cells. The diverse morphology and dynamics of actin structures adapted to versatile cellular functions is established by a large repertoire of actin-binding proteins. The proper interactions with these proteins assume effective molecular adaptations from actin, in which its conformational transitions play essential role. This review attempts to summarise our current knowledge regarding the coupling between the conformational states of actin and its biological function