Affinity chromatography of chymotrypsin on a sepharose derivative coupled with a chymostatin analogue

Measuring Binding Constants of His-Tagged Proteins Using Affinity Chromatography and Ni-NTA Immobilized Enzymes

Affinity chromatography is one way to measure the binding constants of a protein-ligand interaction. Here, we describe a method of measuring a binding constant using Ni-NTA resin to immobilize a His-tagged enzyme and the method of frontal analysis. While other methods of immobilization are possible, using the strong affinity interaction between His-tagged proteins and Ni-NTA supports results in a fast, easy, and gentle method of immobilization. Once the affinity support is created, frontal analysis can be used to measure the binding constant between the protein and various analytes.

Measuring binding constants of His-tagged proteins using affinity chromatography and Ni-NTA-immobilized enzymes

Affinity chromatography is one way to measure the binding constants of a protein-ligand interaction. Here we describe a method of measuring a binding constant using Ni-NTA resin to immobilize a His-tagged enzyme and the method of frontal analysis. While other methods of immobilization are possible, using the strong affinity interaction between His-tagged proteins and Ni-NTA supports results in a fast, easy, and gentle method of immobilization. Once the affinity support is created, frontal analysis can be used to measure the binding constant between the protein and various analytes.

Pig pancreatic anhydro-elastase. Role of the serine-195 hydroxy group in the binding of inhibitors and substrate

The binding constants of a number of ligands were measured for pancreatic elastase (PE) and anhydro-elastase (AE) in order to assess the contribution of Ser-195 to substrate and inhibitor binding by PE. AE was purified by affinity chromatography on a column containing immobilized turkey ovomucoid inhibitor. The AE had 0.1 +/- 0.1% of the activity of the native enzyme and contained 0.8 +/- 0.06 residue of dehydroalanine per molecule. A difference electron-density map, derived from an X-ray crystallographic analysis of AE, showed that the modified residue was Ser-195. The complexing of 3-carboxypropionyl-Ala-Ala-Ala-p-nitroanilide (SAN) to the active site of AE was also demonstrated by X-ray-diffraction analysis of an AE crystal soaked overnight with substrate. The nitroanilide moiety was not observed in the difference map. AE was shown to bind turkey ovomucoid inhibitor with a dissociation constant (Kd) of 0.3 +/- 0.06 microM compared with 0.10 microM for PE. The Kd of the AE-SAN complex (0.2 mM) was comparable with the Michaelis constant for SAN with PE (1.0 mM). A number of inhibitors, such as elastatinal, which forms a hemiketal adduct with PE, while others such as the beta-lactams, which function as acylators of the active-site serine residue, bound AE with a lower affinity than to PE. The binding of a peptidylchloromethane (acetyl-Ala-Ala-Pro-Ala-CH2Cl) to AE occurs without evidence for alkylation of histidine. The binding constants for benzoisothiazolinone and 3,4-dichloroisocoumarin to PE differed from their binding constants to AE by less than a factor of 4.0-fold. The contribution of the hydroxy group of Ser-195 to the binding of these inhibitors to PE in their non-covalent complexes is relatively small, even though they inactivate PE by an acylation mechanism. These results suggest that the hydroxy group on Ser-195 in PE is of secondary importance in the energetics of ligand binding, in contrast with its essential role in the catalytic properties of the enzyme.

The 1.8 A structure of the complex between chymostatin and Streptomyces griseus protease A. A model for serine protease catalytic tetrahedral intermediates

The naturally occurring serine protease inhibitor, chymostatin, forms a hemiacetal adduct with the catalytic Ser195 residue of Streptomyces griseus protease A. Restrained parameter least-squares refinement of this complex to 1.8 A resolution has produced an R index of 0 X 123 for the 11,755 observed reflections. The refined distance of the carbonyl carbon atom of the aldehyde to O gamma of Ser195 is 1 X 62 A. Both the R and S configurations of the hemiacetal occur in equal populations, with the end result resembling the expected configuration for a covalent tetrahedral product intermediate of a true substrate. This study strengthens the concept that serine proteases stabilize a covalent, tetrahedrally co-ordinated species and elaborates those features of the enzyme responsible for this effect. We propose that a major driving force for the hydrolysis of peptide bonds by serine proteases is the non-planar distortion of the scissile bond by the enzyme, which thereby lowers the activation energy barrier to hydrolysis by eliminating the resonance stabilization energy of the peptide bond.