title: Four-fold structural repeat in the acid proteases.
abstract: The observation that the acid proteases contain two structurally equivalent lobes related by a dyad through the active centre has been extended to show that in endothiapepsin each lobe contains two similar halves related by a further local dyad. In lobe 1 22 pairs of alpha-carbons are equivalent with a root mean square deviation of 1.92 A. In lobe 2 17 pairs match within 2.31 A. Convergent evolution or gene quadruplication may have occurred.
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D010434:Pepsin A; D010447:Peptide Hydrolases; D011487:Protein Conformation; D013098:Xylariales / Q000201:enzymology
chemical_list: D010447:Peptide Hydrolases; D010434:Pepsin A