SOME PROPERTIES OF ACID-REASSEMBLED TROPOMYOSIN

The preference for parallelism of the two chains in tropomyosin coiled coils is thought to result from interchain salt bridges. To examine t his ideal, studies are presented of tropomyosin molecules reassembled from chaotropic solvents in acid solution, where cross-links cannot ex ist. The acid-reassembled molecules are appreciably less disulfide cro ss-linkable in acid than native molecules, a result explainable if som e antiparallel dimers indeed form at low pH. Physical studies (backbon e- and tyrosine-region CD and intrinsic viscosity) indicate that refol ding in acid yields a molecular population demonstrably different in t yrosine-region CD from native, but having comparable (but not identica l) helix content, thermal stability, and dimensions. Moreover, the ref olding in acid after either thermal or chaotropic-solvent denaturation yields the same final state, arguing that is an equilibrium state. Al l these results are consistent with, but do not prove, that the acid-r eassembled population includes an appreciable fraction (2/3) of antipa rallel coiled-coil dimers. (C) 1995 John Wiley & Sons, Inc.