英文蛋白质结构.pptVIP

Biochemistry The Sencondary and Three-Dimensional Structure of Proteins Protein Structure 1° structure: the sequence of amino acids in a polypeptide chain, read from the N-terminal end to the C-terminal end 2° structure: the ordered 3-dimensional arrangements (conformations) in localized regions of a polypeptide chain; refers only to interactions of the peptide backbone e. g., ?-helix and ?-pleated sheet Ramachandran Angles ?-Helix ?-Helix coil of the helix is clockwise or right-handed there are 3.6 amino acids per turn repeat distance is 5.4? each peptide bond is s-trans and planar C=O of each peptide bond is hydrogen bonded to the N-H of the fourth amino acid away C=O----H-N hydrogen bonds are parallel to helical axis all R groups point outward from helix ?-Helix Several factors can disrupt an ?-helix proline creates a bend because of (1) the restricted rotation due to its cyclic structure and (2) its ?-amino group has no N-H for hydrogen bonding strong electrostatic repulsion caused by the proximity of several side chains of like charge, e.g., Lys and Arg or Glu and Asp steric crowding caused by the proximity of bulky side chains, e.g., Val, Ile, Thr ?-Pleated Sheet ?-Pleated Sheet ?-Pleated Sheet polypeptide chains lie adjacent to one another; may be parallel or antiparallel R groups alternate, first above and then below plane each peptide bond is s-trans and planar C=O and N-H groups of each peptide bond are perpendicular to axis of the sheet C=O---H-N hydrogen bonds are between adjacent sheets and perpendicular to the direction of the sheet ? -TURN ?-Helices and ?-Sheets Supersecondary structures: the combination of ?- and ?-sections, as for example ??b unit: two parallel strands of ?-sheet connected by a stretch of ?-helix ?? unit: two antiparallel ?-helices ?-meander: an antiparallel sheet formed by a series of tight reverse turns connecting stretches of a polypeptide chain Greek key: a repetitive supersecondary structure formed when an antiparallel