A Supramolecular Polymerization Approach to the Growth of the Myofibril

Molecular recognition mechanisms directing the self-assembly of biological structures

Self-assembling may be defined as the spontaneous association of material units into structures that are often capable of cyclic reorganization and functional behavior. Various molecular recognition processes stabilize assemblies of polymers and biological structures. The present article analyzes cases in which chemical, shape and other recognition mechanisms are individually or cooperatively operative. Simpler self-assembling theories reported in the literature are highlighted. Detailed processes for which chemical recognition is the prevailing, enthalpy-driven, process include the non-ideal component of miscibility, supramolecular polymerization, host-guest complexes and template polymerization. Also discussed are systems such as liquid crystalline closed polymers, ternary mesogenic systems and rigid crystalline polymers for which shape recognition is the prevailing entropy-driven process. Other recognition mechanisms include ion condensation effects, hydrophobic bonding and growth-coupled-to-orientation. Combinations of various recognition mechanisms are particularly evident in biological structures. Self-assembling mechanisms involved in the genesis of some biological systems can be scientifically identified, but much more needs to be known to describe the "engineered" assembling modes that support complex functional organs.

Supramolecular and Liquid Crystalline Contributions to the Assembly of Myofibril

We compare steps observed during the fibrillogenesis of myofibrils with the sequence of steps predictable by a recent analysis of the structurization and functioning of striated muscles. The predicted assembly steps are based solely on fundamental equilibrium processes, particularly supramolecular interactions and liquid crystalline alignment of the rigid thick and thin filaments hosted within the sarcomer. Satisfactory agreement is obtained between several of the observed and the predicted fibrillogenesis steps. In several cases, however, the actual steps appear to be more complex than expected, evidencing the occurrence of transport and kinetic pathways that may assist the attainment of the equilibrium structure. The memory of the order of a precursor mesophase is imprinted during the remodeling of the surfaces at which the two sets of filaments are anchored. The relevance of the present analysis to the functioning of the myofibril is considered.