QUASI-EQUIVALENCE AND NONEQUIVALENCE IN THE STRUCTURE OF BACTERIAL FLAGELLAR FILAMENT

In supercoiled forms of flagellar filaments, which are thought to be p roduced by combinations of two distinct subunit lattices, the lattices are elastically deformed in 11 different ways, depending on their azi muthal positions on the circumference of a tube with 11 protofilaments . Those two interactions are nonequivalent as opposed to quasiequivale nt ones in elastically deformed lattices of otherwise identical intera ctions. The term nonequivalence is defined to represent different bond ing interactions, and quasiequivalent is used to describe deformed but conserved bonding interactions. By using two distinct lattices that w ere accurately determined by x-ray fiber diffraction, 10 possible supe rcoiled forms of flagellar filaments were simulated, based on a bistab le-subunit packing model. Comparison to the observed forms showed good agreement, indicating that the model and determined lattice parameter s effectively represent realistic features of the structure. The simul ated quasiequivalent lattices have been compared to the two nonequival ent lattices, revealing an interesting feature: the maximum deviation in the intersubunit distance by elastic deformation is almost three-qu arters of the difference between the two distinct lattices, demonstrat ing a balanced coexistence of a well-defined conformational distinctio n and extensive adaptability in the molecular structure of flagellin a nd its packing interactions.