Insight into the mechanism of serpin-proteinase inhibition from 2D [1H-15N] NMR studies of the 69 kDa alpha 1-proteinase inhibitor Pittsburgh-trypsin covalent complex. Biochemistry 2001 May 29;40(21):6284-92
Date
05/24/2001Pubmed ID
11371190DOI
10.1021/bi010100xScopus ID
2-s2.0-0035967508 (requires institutional sign-in at Scopus site) 44 CitationsAbstract
We have used [(1)H-(15)N]-HSQC NMR to investigate the structural changes that occur in both serpin and proteinase in forming the kinetically trapped covalent protein-protein complex that is the basis for serpin inhibition of serine proteinases. By alternately using (15)N-alanine specifically-labeled alpha(1)-proteinase inhibitor (alpha(1)PI) Pittsburgh (serpin) and bovine trypsin (proteinase), we were able to selectively monitor structural changes in each component of the 69 kDa complex. Residue-specific assignments of four alanines in the reactive center loop and seven other alanines aided interpretation of the spectral changes in the serpin. We found that the majority of the alanine resonances, including those from reactive center loop residues P12, P11, and P9, were at identical positions in covalent complex and in cleaved alpha(1)PI. Five alanines that are close to the contact region with proteinase showed some chemical shift perturbation compared with cleaved alpha(1)PI, indicating some degree of structural deformation. With (15)N label in the proteinase, an HSQC spectrum was obtained that more closely resembled that of a molten globule, suggesting that the structure of the proteinase had been significantly altered as a result of complex formation. Large increases in line width for all alpha(1)PI resonances in the covalent complex, with the sole exception of two residues in the flexible N-terminal tail, indicate that, unlike the noncovalent alpha(1)PI-anhydroproteinase complex, the covalent complex is a rigid body of effectively increased molecular weight. We conclude that the mutual perturbations of serpin and proteinase result from steric compression and distortion, rather than simple contact effects. This distortion provides a structural basis for the greatly reduced catalytic efficiency of the proteinase in the complex and hence kinetic trapping of the covalent reaction intermediate.
Author List
Peterson FC, Gettins PGAuthor
Francis C. Peterson PhD Professor in the Biochemistry department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
AlanineAnimals
Cattle
Computer Simulation
Hydrolysis
Macromolecular Substances
Models, Molecular
Molecular Weight
Nitrogen Isotopes
Nuclear Magnetic Resonance, Biomolecular
Protons
Serine Endopeptidases
Serine Proteinase Inhibitors
Serpins
Trypsin
alpha 1-Antitrypsin