1. Hydrogen exchange kinetics of bovine pancreatic trypsin inhibitor beta-sheet protons in trypsin-bovine pancreatic trypsin inhibitor, trypsinogen-bovine pancreatic trypsin inhibitor, and trypsinogen-isoleucylvaline-bovine pancreatic trypsin inhibitor
P Brandt, C Woodward Biochemistry. 1987 Jun 2;26(11):3156-67. doi: 10.1021/bi00385a032.
Hydrogen exchange rates of six beta-sheet peptide amide protons in bovine pancreatic trypsin inhibitor (BPTI) have been measured in free BPTI and in the complexes trypsinogen-BPTI, trypsinogen-Ile-Val-BPTI, bovine trypsin-BPTI, and porcine trypsin-BPTI. Exchange rates in the complexes are slower for Ile-18, Arg-20, Gln-31, Phe-33, Tyr-35, and Phe-45 NH, but the magnitude of the effect is highly variable. The ratio of the exchange rate constant in free BPTI to the exchange rate constant in the complex, k/kcpIx, ranges from 3 to much greater than 10(3). Gln-31, Phe-45, and Phe-33 NH exchange rate constants are the same in each of the complexes. For Ile-18 and Tyr-35, k/kcpIx is much greater than 10(3) for the trypsin complexes but is in the range 14-43 for the trypsinogen complexes. Only the Arg-20 NH exchange rate shows significant differences between trypsinogen-BPTI and trypsinogen-Ile-Val-BPTI and between porcine and bovine trypsin-BPTI.
2. The refined 2.2-A (0.22-nm) X-ray crystal structure of the ternary complex formed by bovine trypsinogen, valine-valine and the Arg15 analogue of bovine pancreatic trypsin inhibitor
W Bode, J Walter, R Huber, H R Wenzel, H Tschesche Eur J Biochem. 1984 Oct 1;144(1):185-90. doi: 10.1111/j.1432-1033.1984.tb08447.x.
Large orthorhombic crystals of the complex formed by bovine trypsinogen and a semisynthetic homologous bovine pancreatic trypsin inhibitor with the reactive-site lysine residue replaced by an arginine residue [( Arg15]PTI) have been obtained which are isomorphous with the crystals of PTI-trypsinogen [Bode, W., Schwager, P. and Huber, R. (1978) J. Mol. Biol. 118, 99-112]. The X-ray crystal structure of the ternary complex of trypsinogen-[Arg15]PTI with the dipeptide Val-Val has been determined by X-ray data to 2.2-A (0.22-nm) resolution by means of difference Fourier methods and has been crystallographically refined to a final R-value of 0.17. Replacement of the reactive-site Lys15 by an arginine residue is accompanied in the complex by small movements of polar side groups of trypsin and enclosed solvent molecules within the specificity pocket. Only solvent molecule 414 OH which mediates the hydrogen bond interactions between Lys15 NZ and Asp189 carboxylate is expelled, thus allowing the bulkier guanidyl group to approach this carboxylate. The dipeptide Val-Val binds in the pocket accepting the Ile-Val N-terminus in trypsin. The cavity left by the CD-methyl group of Ile16 upon replacement by a valine residue is only partially filled by slight rearrangements of neighbouring peptide side chains. Part of the positive free energy change observed upon replacement of Ile-Val may allow for the maintenance of this cavity.
3. High-level bacterial expression and 15N-alanine-labeling of bovine trypsin. Application to the study of trypsin-inhibitor complexes and trypsinogen activation by NMR spectroscopy
F C Peterson, N C Gordon, P G Gettins Biochemistry. 2001 May 29;40(21):6275-83. doi: 10.1021/bi0100992.
We describe here the high-level expression of bovine trypsinogen in E. coli, its refolding and activation to beta-trypsin, and the selective incorporation of (15)N-labeled alanine through supplementation of the growth medium. Using this procedure, we expressed (15)N-labeled S195A trypsinogens, both on a wild-type and on a D189S background, in amounts suitable for NMR spectroscopy. 2D [(1)H-(15)N]-HSQC NMR was used to follow conformational changes upon activation of trypsinogen and formation of noncovalent complexes between S195A or S195A/D189S trypsin and protein proteinase inhibitors of different structural families and different sizes, as well as to examine the effects of introduction of the D189S mutation. Spectra of good quality were obtained for both trypsins alone and in complexes of increasing size with the proteinase inhibitors BPTI (total molecular mass 31 kDa), SBTI (total molecular mass 44 kDa), and the serpin alpha(1)-proteinase inhibitor Pittsburgh (alpha(1)PI Pittsburgh) (total molecular mass 69 kDa). Assignments of alanines 55 and 56, close to the active site histidine, and of alanine 195, present in the S195A variant used for most of the studies, were made by mutagenesis. These three alanines, together with two others, probably close to the S1 specificity pocket, were very sensitive to complex formation. In contrast, the remaining 10 alanines were invariant in chemical shift in all 3 of the noncovalent complexes formed, reflecting the conservation of structure in complexes with BPTI and SBTI known from X-ray crystal structures, but also indicating that there is no change in backbone conformation for the noncovalent complex with alpha(1)PI, for which there is no crystal structure. This was true both for S195A and for S195A/D189S trypsins. This high-level expression and labeling approach will be of great use for solution NMR studies on trypsin-serpin complexes, as well as for structural and mechanistic studies on trypsin variants.
