Bioinspired materials: Physical properties governed by biological refolding

Abstract

Peptide and protein biomolecules folded into two fundamentally different conformations, either α-helical or β-sheet, carry out dissimilar biological functions. In living organisms, an α-helical secondary structure is adopted by different types of proteins such as myoglobin, keratin, collagen, and more. They can be found in diverse biological tissues of muscle, bone, cartilage, etc.. Biological functions of β-sheet peptide/protein structures are different and associated with a wide range of human mental amyloid diseases such as Alzheimer and Parkinson. The fundamental basis of these diseases is misfolding or refolding of natively soluble α-helical amyloid proteins into solid-state β-sheet fibrillary structures. Bioinspired chemically synthesized biomolecules mimic their biological counterparts. Although these artificial and biological peptides/proteins molecules are completely dissimilar in origin and environment, they demonstrate the common properties of folding and refolding into identical secondary architectures. In this review, we show that these two structural conformations, native (helix-like) and β-sheet, exhibit exclusive and different sets of fold-sensitive physical properties that are surprisingly similar in both biological and bioinspired materials. A native (helix-like) self-assembled fold having asymmetric structure demonstrates ferroelectric-like pyroelectric, piezoelectric, nonlinear optical, and electro-optical effects. β-sheet peptide/protein structures acquire unique visible fluorescence (FL) and reveal a new property of lossless FL photonic transport followed by a long-range FL waveguiding in amyloidogenic fibers. An applied thermally mediated refolding native-to-β-sheet allows us to observe adoption, disappearance, and switching of the revealed physical properties in detail in each fold and study dynamics of all critical stages of refolding from the metastable (native) helix-like conformation via intermediate disordered state to stable β-sheet fibrillary ordering. In the intermediate state, the appearance of the visible FL provides imaging, monitoring, and direct observation of the early stages of seeding and nucleation of β-sheet fibrils. The diverse fold-sensitive physical properties found, give a new insight into biological refolding processes and pave the way for the development of advanced physical methods of fold recognition, bioimaging, light theranostics at nanoscale, and peptide/protein nanophotonics from new visible FL bionanodots to bioinspired multifunctional peptide photonic chips.