Influence of the complex formation between trypsin and bovine basic trypsin inhibitor on the reactivity of certain disulfide bonds

Modelling of the serine-proteinase fold by X-ray and neutron scattering and sedimentation analyses: occurrence of the fold in factor D of the complement system

Solution scattering is a powerful means of determining the overall arrangement of domains in the multidomain proteins of complement. the serine-proteinase domain is central to all proteolytic events during complement activation. As models of this domain, bovine beta-trypsin, trypsinogen, alpha-chymotrypsin and chymotrypsinogen A were studied by neutron and X-ray synchrotron solution scattering. At pH 7, all the X-ray and neutron M(r) values corresponded to monomeric proteins. The X-ray radii of gyration, RG, of beta-trypsin, trypsinogen, alpha-chymotrypsin and chymotrypsinogen A (measured in positive solute-solvent contrasts) were 1.59 nm, 1.78 nm, 1.71 nm and 1.76 nm (+/- 0.05-0.11 nm) in that order. Neutron contrast variation showed that the RG at infinite contrast, RC, for these four proteins were 1.57 nm, 1.70 nm, 1.67 nm and 1.78 nm (+/- 0.03 nm) in that same order. The radial inhomogeneity of neutron-scattering density, alpha, was positive at (5-13) x 10(-5), and corresponds to the preponderance of hydrophilic residues near the protein surface. On trypsinogen activation, a small reduction in the RG value of 0.13 +/- 0.07 nm was just detectable, while the RG of chymotrypsinogen A was unchanged after activation. The RC and alpha values of the four proteins can be calculated by using crystallographic co-ordinates. The reduced RG of beta-trypsin relative to trypsinogen was explained in terms of the removal of the extended N-terminal hexapeptide of trypsinogen. The full X-ray and neutron-scattering curves in positive and negative contrasts agreed well with scattering curves calculated from crystallographic coordinates to a nominal structural resolution of 4.5 nm, provided that the internal structure was considered in neutron modelling, and that the hydration was considered in X-ray modelling. Sedimentation-coefficient data also provide information on the disposition of domains in multidomain proteins. It was found that the hydrated X-ray sphere model could be directly utilized to calculate sedimentation coefficients. X-ray scattering on factor D showed from its RG of 1.78 nm that this is monomeric and very similar in structure to beta-trypsin. The X-ray-scattering curve of factor D was readily modelled using the beta-trypsin crystal structure after allowance for sequence changes. The success of these modellings provides a basis for the constrained modelling of solution scattering data for the multidomain proteins of complement.

Novel version of Multiple Antigenic Peptide allowing incorporation on a cysteine functionalized lysine tree

A novel version of Multiple Antigenic Peptide (MAP) is described. This approach consists of the synthesis of a properly functionalized antigen carrier and the incorporation, on request, of one or more activated antigenic peptides. This method was to synthesize a MAP containing eight epitopes of Hsp 70-1 from Plasmodium falciparum. Mice immunised with this MAP gave a specific response while those immunised with the peptide alone did not.

Complete tyrosine assignments in the high-field 1H nuclear magnetic resonance spectrum of bovine pancreatic trypsin inhibitor selectively reduced and carboxamidomethylated at cystine 14-38

The low-field portions of the 250-MHz 1H nuclear magnetic resonance spectra of native and chemically modified basic pancreatic trypsin inhibitor have been studied as a function of pH over the range pH 5-13. In derivatives selectively reduced and carboxamidomethylated at cystine 14-38, resonances associated with 15 of the 16 protons of the aromatic rings of the four tyrosines of the inhibitor have been located and assigned to specific tyrosyl residues. Titrations of pH yielded pK's for tyrosines 10, 21, 23, and 35 in the modified inhibitor of 9.9, 10.6, 11.6, and 11.0, respectively. Resonances associated with the three nitrotyrosine 10 protons of the mononitrated derivative and the six nitrotyrosine 10 and 21 protons of the dinitrated derivative have been similarly located, assigned, and titrated, yielding pK's for nitrotyrosines 10 and 21 of 6.5 and 6.4, respectively. Previously reported results for derivatives with cystine 14-38 intact have been revised on the basis of new data. Comparison of these revised results with the new data for derivatives with modified cystine 14-38 reveals no changes in pK's for any tyrosine or nitrotyrosing ring and no changes in chemical shift for resonances of nitrotyrosine 21 or tyrosines 21 and 23. However, modification of cystine 14-38 causes significant changes in chemical shifts of resonances of the nearby nitrotyrosine 10 and tyrosine 10 and 35 rings. Tyrosine 35 remains relatively immobile, rotating less than 1600 times/s at 25 degrees C for pH's in the range 5-13.

The reactive sites of Kunitz bovine-trypsin inhibitor. Role of lysine-15 in the interaction with chymotrypsin

Kunitz bovine trypsin inhibitor gave with alpha-chymotrypsin a stoichiometric complex stable at neutral pH. The complex has been characteristized by amino acid composition, molecular sieving and zone electrophoresis. Complete dissociation occurred at pH 4.0 as shown by gel filtration, alpha-Chymotrypsin was displaced from the complex by trypsin either in solution or by affinity chromatography on trypsin-Sepharos: alpha-chymotrypsin was recovered in the filtrate (yield about 100%) and the inhibitor was eluted from trypsin-Sepharose with 0.1 M HCl (yield: 83%). Lysine-15 of the inhibitor was shown to be involved in the interaction between alpha-chymotrypsin and the inhibitor. When the complex was maleylated, the maleylated chymotrypsin-bound inhibitor was displaced by affinity chromatography on trypsin-Sepharose. Teh recovered derivative was oxidized, subjected to tryptic hydrolysis and the products separated by peptide mapping and analyzed. The peptides were compared with those obtained with non-maleylated inhibitor and fully maleylated free inhibitor. In the fully maleylated inhibitor, the four lysyl residues of the molecule were blocked but in the maleylated chymotrypsin-bound inhibitor, Lys-15 was unmodified in contrast to Lys-26, Lys-41 and Lys-46; therefore Lys-15 is shielded by chymotrypsin in the complex. On the other hand, when inhibitor with a selectively reduced carboxamidomethylated Cys-14-Cys-38 dislufide bridge was allowed to react with chymotrypsin, cleavage occurred not only at Tyr-21, Tyr-35 and Phe-45 but also at Lys-15, cleavage not observed in the case of the fully oxidized inhibitor. This result shows that under particular conditions the bond Lys-15-Ala-16 can be the substrate for chymotrypsin and the side chain of Lys-15 can be inserted in the chymotrypsin specificity pocket. Apparently the contact area of inhibitor with chymotrypsin seems to be similar to that with trypsin [J. Chauvet and R. Acher (1967) J. Biol. Chem. 242, 4274-4275].