Primary Secondary Tertiary Quaternary strueture strueture structure strueture Gly Leu Amino acid residues a helix Polypeptide chain Assembled subunits
3.3 Studies of protein conformation, function, and evolution have revealed importance of two other levels of organization. 3.3.1 The supersecondary structure refers to clusters of secondary structures that repeatedly appear in different proteins. 3.3.2 The already identified supersecondary structures include mainly BaB motif, Greek key motif, β- hairpin loop, four-helix- bundle,…etc. 3.3.3 Supersecondary structure motifs are usually also folding motifs of proteins. (a conjecture, Not completely established experimentally)
3.3 Studies of protein conformation, function, and evolution have revealed importance of two other levels of organization. 3.3.1 The supersecondary structure refers to clusters of secondary structures that repeatedly appear in different proteins. 3.3.2 The already identified supersecondary structures include mainly bab motif, Greek key motif, b-hairpin loop, four-helix-bundle, …etc. 3.3.3 Supersecondary structure motifs are usually also folding motifs of proteins. (a conjecture, Not completely established experimentally)
3.3.4 A compact region(usually include less than 200-400 residues) that is a distinct structural unit within a larger polypeptide chain is called a domain 3.3.5 Many domains fold independently into thermodynamically stable structures, and sometimes, have separate functions
3.3.4 A compact region (usually include less than 200~400 residues) that is a distinct structural unit within a larger polypeptide chain is called a domain. 3.3.5 Many domains fold independently into thermodynamically stable structures, and sometimes, have separate functions
table 6-2 Approximate Amounts of a Helix and B Conformation in some single-Chain proteins Residues (% Protein (total residues) a helix β Conformation Chymotrypsin (247) 14 Ribonuclease(124) 26 35 Carboxypeptidase(307) 38 17 Cytochrome c(104) 39 0 Lysozyme (129) 12 Myoglobin (153) 0 Source: Data from Cantor, C.R.& Schimmel, P.R.(1980)Biophysical Chemistry, Part I: The Conformation of Biological Macromolecules, p. 100, W.H. Freeman and Company, New York Portions of the polypeptide chains that are not accounted for by a helix or B conformation consist of bends and irregularly coiled or extended stretches. Segments of a helix and B conformation sometimes deviate slightly from their normal dimensions and geometry
Structural domains in the polypeptide troponin C, two separate calcium-binding domains
Structural domains in the polypeptide troponin C, two separate calcium-binding domains