The 2.5 A X-ray crystal structure of the acid-stable proteinase inhibitor from human mucous secretions analysed in its complex with bovine alpha-chymotrypsin.
Orthorhombic crystals of the complex formed between bovine alpha-chymotrypsin and a recombinant human mucous proteinase inhibitor (SLPI) were grown. Data to 2.3 A resolution were collected on the area-detector diffractometer FAST. The crystal structure of the complex was solved by Patterson search techniques using chymotrypsin as a search model. A cyclic procedure of modeling and crystallographic refinement enabled the determination of the SLPI structure. The current crystallographic R-value is 0.19. SLPI has a boomerang-like shape with both wings comprising two well separated domains of similar architecture. In each domain the polypeptide chain is arranged like a stretched spiral. Two internal strands form a regular beta-hairpin loop which is accompanied by two external strands linked by the proteinase binding segment. The polypeptide segment of each domain is interconnected by four disulfide bridges with a connectivity pattern hitherto unobserved. The reactive site loop of the second domain has elastase and chymotrypsin binding properties. It contains the scissile peptide bond between Leu72I and Met73I and has a similar conformation to that observed in other serine proteinase protein inhibitors. Eight residues of this loop, two of the adjacent hairpin loop, the C-terminal segment and Trp30I are in direct contact with the cognate enzyme. The binding loop of the first domain (probably with anti-trypsin activity) is disordered due to proteolytic cleavage occurring in the course of crystallization.
Grütter
M G
MG
Max-Planck-Institut für Biochemie, Martinsried, FRG.
Fendrich
G
G
Huber
R
R
Bode
W
W
D000595:Amino Acid Sequence; D000818:Animals; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism*; D003198:Computer Simulation; D004220:Disulfides / Q000032:analysis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D009092:Mucous Membrane / Q000378:metabolism*; D011480:Protease Inhibitors / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000378:metabolism*; D014961:X-Ray Diffraction
D004220:Disulfides; D011480:Protease Inhibitors; D011994:Recombinant Proteins; D002918:Chymotrypsin