PDBsum entry 1a0l

Hydrolase/hydrolase inhibitor

PDB id: 1a0l

Contents

Protein chain

244 a.a. *

Ligands

APA ×4

Waters ×96

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Human beta-Tryptase is a ring-Like tetramer with active sites facing a central pore.

Authors

P.J.Pereira, A.Bergner, S.Macedo-Ribeiro, R.Huber, G.Matschiner, H.Fritz, C.P.Sommerhoff, W.Bode.

Ref.

Nature, 1998, 392, 306-311. [DOI no: 10.1038/32703]

PubMed id

9521329

Abstract

Human tryptase, a mast-cell-specific serine proteinase that may be involved in causing asthma and other allergic and inflammatory disorders, is unique in two respects: it is enzymatically active only as a heparin-stabilized tetramer, and it is resistant to all known endogenous proteinase inhibitors. The 3-A crystal structure of human beta-tryptase in a complex with 4-amidinophenyl pyruvic acid shows four quasi-equivalent monomers arranged in a square flat ring of pseudo 222 symmetry. Each monomer contacts its neighbours at two different interfaces through six loop segments. These loops are located around the active site of beta-tryptase and differ considerably in length and conformation from loops of other trypsin-like proteinases. The four active centres of the tetramer are directed towards an oval central pore, restricting access for macromolecular substrates and enzyme inhibitors. Heparin chains might stabilize the complex by binding to an elongated patch of positively charged residues spanning two adjacent monomers. The nature of this unique tetrameric architecture explains many of tryptase's biochemical properties and provides a basis for the rational design of monofunctional and bifunctional tryptase inhibitors.

Figure 1.
Figure 1 Solid-surface representation of the tryptase tetramer. The colours indicate positive (blue) and negative (red) electrostatic potential at the molecular surface. Figures made with GRASP28. a, Front view. The four monomers (labelled A to D) are arranged at the corners of a flat square. Horizontal and vertical local two-fold symmetry axes, relating monomer A (or D) with B (or C), and monomer A (or B) with D (or C), respectively, run through the tetramer centre, as does a third, perpendicular, axis. The four monomers leave a central pore. Two of the four bound APPA molecules (yellow) are visible, whereas the two others are shielded by projecting flaps. The (blue) patches of positively charged residues at the surfaces of monomers B and D extend towards the A-B and C-D peripheries. b, Edge view towards the C-D dimer. The tetramer has been rotated around a vertical axis by almost 90° compared with a, clearing the view towards the peripheral sides of monomers C (bottom) and D (top). The positively charged patches on both monomers extend towards the front side (right) of D and the back side (left) of C. An extended heparin chain of almost 100 ? could span both patches, strengthening the small C-D and A-B contacts.

Figure 2.
Figure 2 Ribbon representation of one tryptase monomer in the standard orientation. Monomer A of Fig. 1a is shown after rotation around a vertical axis by 90° (the rotation used to create Fig. 1b). The view is towards the active centre (represented by Ser 195, His 57 and Asp 102 as yellow stick models), with the active-site cleft running from left to right; the APPA molecule interacts with Asp 189 (yellow stick models) in the S1 pocket. The six unique surface loops of tryptase surrounding the active site and engaged in intermonomer contacts are specifically coloured. The 147 loop is light blue; the 70-80 loop is yellow; the 37 loop is orange; the 60 loop is mauve; the 97 loop is green; and the 173 flap is red. All other tryptase segments are violet. Figure produced with Insight II (Biosym/MSI, San Diego).

The above figures are reprinted by permission from Macmillan Publishers Ltd: Nature (1998, 392, 306-311) copyright 1998.