1PCA

THREE DIMENSIONAL STRUCTURE OF PORCINE PANCREATIC PROCARBOXYPEPTIDASE A. A COMPARISON OF THE A AND B ZYMOGENS AND THEIR DETERMINANTS FOR INHIBITION AND ACTIVATION

1PCA の概要

• エントリーDOI: 10.2210/pdb1pca/pdb
• 分子名称: PROCARBOXYPEPTIDASE A PCPA, ZINC ION, CITRIC ACID, ... (5 entities in total)
• 機能のキーワード: hydrolase(c-terminal peptidase)
• 由来する生物種: Sus scrofa (pig)
• 細胞内の位置: Secreted: P09954
• タンパク質・核酸の鎖数: 1
• 化学式量合計: 45678.45

構造登録者

Guasch, A.,Coll, M.,Aviles, F.X.,Huber, R. (登録日: 1991-10-28, 公開日: 1993-10-31, 最終更新日: 2024-10-30)

主引用文献

Guasch, A.,Coll, M.,Aviles, F.X.,Huber, R.
Three-dimensional structure of porcine pancreatic procarboxypeptidase A. A comparison of the A and B zymogens and their determinants for inhibition and activation.
J.Mol.Biol., 224:141-157, 1992

PubMed Abstract: The three-dimensional structure of procarboxypeptidase A (PCPA) from porcine pancreas has been determined at 2 A resolution and refined to a crystallographic R-factor of 0.198, with a root-mean-square deviation from ideal values for bond lengths of 0.015 A and for angles of 2.1 degrees. It is compared with procarboxypeptidase B (PCPB) from the same tissue. The 94/95 residue activation segments of PCPA/PCPB have equivalent folds: an N-terminal globular region with an open sandwich antiparallel alpha/antiparallel beta topology, followed by an extended alpha-helical segment, the connection to the enzyme. Alignment of the secondary structures of the activation segments of PCPA and PCPB (residues A1 to A99) indicates a two residue insertion between residues A34 and A35 and a C-terminal helix that is two turns longer in PCPA compared to PCPB. A deletion is observed between residues A43 to A45, the region containing the short 3(10) helix that covers the active site in PCPB. The globular region (A4 to A80) shields the preformed active center of carboxypeptidase A (CPA), but none of the residues involved in catalysis makes direct contacts with the activation segment. In contrast, subsites S2, S3 and S4 of the enzyme, involved in the binding of peptidic substrates, are blocked by specific contacts with residues AspA36, TrpA38, ArgA47, AspA53 and GluA86 of the activation segment. It has been described that several residues of CPA exhibit different conformations in the free enzyme compared to when substrate is bound: Arg127, Arg145, Glu270 and Tyr248. In PCPA all of these residues are found in the "active" conformation, as if substrate were actually bound. The presence of a ligand, tentatively interpreted as a free amino acid (Val) in the active center could explain this fact. The connecting region (A80 to A99), the target for proteolytic activation, establishes fewer contacts with the enzyme in PCPA than in PCPB. The activation segment of PCPA (A4 to A99) remains bound to the enzyme after the first trypsin cleavage between ArgA99-Ala1 probably due to the stability conferred on it by the alpha-helix (alpha 3) of the connecting segment. These and other structural features may explain the differences in intrinsic activity and different rates or proteolytic activation of each zymogen.

PubMed: 1548696
DOI: 10.1016/0022-2836(92)90581-4

実験手法

X-RAY DIFFRACTION (2 Å)