Role of cooperativity in protein folding and protein mosaic assemblage relevance for protein conformational diseases

Biological systems are organized in intricate and highly structured networks with hierarchies and multiple scales. Cells can be considered as "meso-scale level" systems placed between the "macro-scale level" (systems of cellular networks) and the "micro-scale level" (systems of molecular networks). In fact, cells represent complex biochemical machineries made by networks of molecules connected by biochemical reactions. Thus, the brain should be studied as a system of "networks of networks". Recently, the existence of a Global Molecular Network (GMN) enmeshing the entire CNS was proposed. This proposal is based on the evidence that the extra-cellular matrix is a dynamic molecular structure capable of storing and releasing signals and of interacting with receptors and proteins on the cell membranes. Proteins have a special role in molecular networks since they can be assembled into high-order molecular complexes, which have been defined as Protein Mosaics (PM). Protein monomers in a PM (the "tesserae" of the mosaic) can interact via classical and non-classical cooperativity behaviour involving allosteric interactions. In the present paper, new features of allostery and cooperativity for protein folding, assemblage and topological features of PM will be discussed. Against this background, alterations in PM via allosteric modulations and non-classical cooperativity mechanisms may lead to protein aggregates like beta amyloid fibrils. Such aggregates cause pathological changes in the GMN structure and function leading to neurodegenerative diseases such as Alzheimer's disease. Thus, a novel view of the so called Protein Conformational Diseases (PCD) is proposed.