title: Protein folding: understanding the role of water and the low Reynolds number environment as the peptide chain emerges from the ribosome and folds.
abstract: The mechanism of protein folding during early stages of the process has three determinants. First, moving water molecules obey the rules of low Reynolds number physics without an inertial component. Molecular movement is instantaneous and size insensitive. Proteins emerging from the ribosome move and rotate without an external force if they change shape, forming and propagating helical structures that increases translocational efficiency. Forward motion ceases when the shape change or propelling force ceases. Second, application of quantum field theory to water structure predicts the spontaneous formation of low density coherent units of fixed size that expel dissolved atmospheric gases. Structured water layers with both coherent and non-coherent domains, form a sheath around the new protein. The surface of exposed hydrophobic amino acids is protected from water contact by small nanobubbles of dissolved atmospheric gases, 5 or 6 molecules on average, that vibrate, attracting even widely separated resonating nanobubbles. This force results from quantum effects, appearing only when the system is within and interacts with an oscillating electromagnetic field. The newly recognized quantum force sharply bends the peptide and is part of a dynamic field determining the pathway of protein folding. Third, the force initiating the tertiary folding of proteins arises from twists at the position of each hydrophobic amino acid, that minimizes surface exposure of the hydrophobic amino acids and propagates along the protein. When the total bend reaches 360°, the leading segment of water sheath intersects the trailing segment. This steric self-intersection expels water from overlapping segments of the sheath and by Newton׳s second law moves the polypeptide chain in an opposite direction. Consequently, with very few exceptions that we enumerate and discuss, tertiary structures are absent from proteins without hydrophobic amino acids, which control the early stages of protein folding and the overall shape of protein. Consequently, proteins only adopt a limited number of forms. The formation of quaternary structures is not necessarily prevented by the absence of hydrophobic amino acids.
authors.affiliation: CRANN, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Sen
authors.affiliation: School of Biochemistry and Immunology, Trinity College Dublin, Dublin 2, Ireland.
authors.forename: H Paul
authors.initials: HP
authors.lastname: Voorheis
mesh_terms: D057446:Hydrodynamics; D057927:Hydrophobic and Hydrophilic Interactions; D008954:Models, Biological; D010455:Peptides / Q000737:chemistry*; D014176:Protein Biosynthesis / Q000502:physiology*; D017510:Protein Folding; D014867:Water / Q000737:chemistry*
chemical_list: D010455:Peptides; D014867:Water
keywords: Coherent domains; Protein biosynthesis; Quantum field theory; Role of hydophobic amino acids; Water sheath