Protein Structure

Linear sequence of amino acids joined by peptide bonds, numbered from N- to C-terminus. Sequence alone (Anfinsen 1961) encodes the folded…

Local backbone conformation stabilised by hydrogen bonds between amide N-H and carbonyl C=O groups. Canonical elements: α-helix, β-sheet,…

Right-handed spiral with 3.6 residues per turn, 1.5 Å rise per residue, i→i+4 H-bonds. Pauling-Corey-Branson 1951 — predicted before…

Extended backbone conformation with inter-strand H-bonds; parallel or antiparallel. Side chains alternate above/below the sheet plane.

φ (N-Cα) vs ψ (Cα-C) dihedral angle scatter for protein residues; allowed regions cluster around α-helix (-60,-45), β-sheet (-120,120),…

Entropically-driven clustering of nonpolar side chains away from water; dominant force collapsing polypeptides into compact folds (Kauzmann…

3D fold of a single polypeptide chain — packing of secondary-structure elements into domains stabilised by hydrophobic core, H-bonds, salt…

Assembly of multiple subunits (homo- or heteromeric) into a functional complex. Examples: haemoglobin α2β2, ATP synthase, ribosome, 20S…

Kinetic+thermodynamic process by which a polypeptide reaches its native fold. Levinthal's paradox resolved by funnel-shaped energy…

Native fold of a small globular protein is determined entirely by its primary sequence under physiological conditions (ribonuclease A…

Protein that assists folding of other proteins without being part of the final structure. Major families: Hsp70 (DnaK), Hsp90, chaperonins…

ATP-dependent chaperone that binds exposed hydrophobic segments on nascent/misfolded chains. Works with J-domain co-chaperones (Hsp40/DnaJ)…

ATP-dependent dimer chaperone that matures signalling clients (kinases, steroid receptors). Drug target in oncology (geldanamycin, 17-AAG).

Bacterial chaperonin: GroEL (14-mer double ring) + GroES (7-mer lid) sequester misfolded substrate in a hydrophilic Anfinsen cage for…

Protein or region lacking stable tertiary structure under native conditions, often rich in charged/polar residues. Involved in signalling…

Compact, independently folding unit of ~50-250 residues with conserved sequence and structure. SCOP/CATH classify ~1400 folds;…

Covalent modification of residues after translation: phosphorylation, acetylation, methylation, ubiquitination, SUMOylation, glycosylation,…

Reversible addition of a phosphate group to Ser/Thr/Tyr (eukaryotes) or His/Asp (two-component). Regulates ~30% of eukaryotic proteome;…

Covalent attachment of 76-residue ubiquitin via isopeptide bond to Lys side chain. K48 polyubiquitin targets proteasomal degradation; K63…

Attachment of oligosaccharide chains to Asn (N-linked, Sec61-translocon) or Ser/Thr (O-linked). Occurs in ER/Golgi; regulates folding,…