Calorimetric and spectroscopic examination of the solution phase structures of prekallikrein binding domain peptides of high molecular weight kininogen

Fourier transform infrared (FT-IR) spectroscopic studies of peptide models for interaction of the binding regions of high molecular weight kininogen and prekallikrein

The binding sites for high molecular weight kininogen (HK) on prekallikrein (PK) are composed of two discontinuous segments in the primary sequence, one in Apple 1 domain (PK56=F56-G86) and the other in Apple 4 (PK266=K266-G295). The site on HK, HK31, is subsumed in a 31-amino-acid sequence (S565-K595) near the C-terminus which has the same affinity for prekallikrein as the entire HK molecule. The binding among them is likely due to conformational changes which serve to juxtapose the PK binding domain within HK with the HK binding site. Resolution-enhanced Fourier transform infrared spectroscopy (FT-IR) has been employed to analyze the contents of secondary structural elements of PK56 and HK31 and to reveal the possible specific binding portion and structural changes in HK31 and PK56 upon binding. From the amide I bands of their deconvoluted FT-IR spectra, it is known that PK56 contains no helix component, while HK31 has two different helical conformations. A quantitative comparison of the spectra of HK31, PK56 and their binding complex suggests that the conformation of 3(10)-helix in HK31 has been changed to an alpha-helix, and one disordered segment of PK56 may have been changed to extended conformation. The other structural components in PK56 and HK31 remain unchanged. Since previous studies have shown that these peptides mimic the natural protein in their bioactivity, their interaction may reflect similar changes in the natural molecules.

High Molecular Weight Kininogen Peptides Inhibit the Formation of Kallikrein on Endothelial Cell Surfaces and Subsequent Urokinase-Dependent Plasmin Formation

A sequence of 31 amino acids (S565-K595) in domain 6 of the light chain of high molecular weight kininogen (HK) has previously been shown to be responsible for the binding of plasma prekallikrein (PK) or kallikrein. To find effective peptides that might block binding between HK and PK on cell surfaces, a new series of synthetic peptides has now been prepared that incorporates portions of this binding domain sequence. For mapping the minimal sequence within HK, these new peptides were tested for their ability to compete with HK for binding PK in a cell-free system and on human umbilical vein endothelial cells (HUVEC). In the former, at pH 7.4, the kds for binding between kallikrein and either D567-K595, S565-P594, D567-S593, or D567-T591 were all similar to that for the binding of S565-K595 (0.2 to 0.4 μmol/L), but those for the binding of D568-K595, W569-K595, and D567-P589 were an order of magnitude greater (kd = 2 to 5 μmol/L). D567-S586, the shortest chain length of the N- and C-terminal truncation sequences tested, does not effectively compete with kininogen for kallikrein binding (kd = 100 μmol/L). These results imply that D567-T591, a 25-residue peptide (HK25c), contains sufficient structural information for binding kallikrein in solution. D567-T591 also is the minimum structural sequence to block binding of kallikrein to HUVEC-bound HK (IC50 = 50 nmol/L) and to inhibit PK activation to kallikrein on the cell surface (IC50 = 80 nmol/L). In addition, D567-T591 also inhibits the generation of kallikrein-activated urokinase, which activates plasminogen to plasmin (IC50 = 100 nmol/L). Thus, HK-derived peptides may be useful compounds for modulating excessive fibrinolysis and hypotension in sepsis and multiple trauma.

High Molecular Weight Kininogen Peptides Inhibit the Formation of Kallikrein on Endothelial Cell Surfaces and Subsequent Urokinase-Dependent Plasmin Formation

A sequence of 31 amino acids (S565-K595) in domain 6 of the light chain of high molecular weight kininogen (HK) has previously been shown to be responsible for the binding of plasma prekallikrein (PK) or kallikrein. To find effective peptides that might block binding between HK and PK on cell surfaces, a new series of synthetic peptides has now been prepared that incorporates portions of this binding domain sequence. For mapping the minimal sequence within HK, these new peptides were tested for their ability to compete with HK for binding PK in a cell-free system and on human umbilical vein endothelial cells (HUVEC). In the former, at pH 7.4, the kds for binding between kallikrein and either D567-K595, S565-P594, D567-S593, or D567-T591 were all similar to that for the binding of S565-K595 (0.2 to 0.4 μmol/L), but those for the binding of D568-K595, W569-K595, and D567-P589 were an order of magnitude greater (kd = 2 to 5 μmol/L). D567-S586, the shortest chain length of the N- and C-terminal truncation sequences tested, does not effectively compete with kininogen for kallikrein binding (kd = 100 μmol/L). These results imply that D567-T591, a 25-residue peptide (HK25c), contains sufficient structural information for binding kallikrein in solution. D567-T591 also is the minimum structural sequence to block binding of kallikrein to HUVEC-bound HK (IC50 = 50 nmol/L) and to inhibit PK activation to kallikrein on the cell surface (IC50 = 80 nmol/L). In addition, D567-T591 also inhibits the generation of kallikrein-activated urokinase, which activates plasminogen to plasmin (IC50 = 100 nmol/L). Thus, HK-derived peptides may be useful compounds for modulating excessive fibrinolysis and hypotension in sepsis and multiple trauma.

Physical and biological significance of peptide sequences mediating the interaction between high molecular weight kininogen and plasma prekallikrein

HK31 (S565-K595) has previously been shown to encompass the binding domain for plasma prekallikrein (PK) within domain 6 of high molecular weight kininogen (HK). The complementary binding domain for HK within PK is mapped to PK56 (F56-G86), in the Apple 1 domain and to PK266 (K266-C295) in the Apple 4 domain. Isothermal titration calorimetry demonstrated that either PK peptide binds to HK31 in 1:1 stoichiometry. Binding of the alternate PK peptide into a ternary complex is facilitated nearly 2-fold. Fluorescence emission spectroscopy revealed that only the binding of PK56 caused a limited decrease in intrinsic tryptophane fluorescence emission intensity of HK31. We conclude that the two PK peptides bind to the HK peptide at different sites. To map the minimal sequence within HK31, truncated new peptides were tested for their ability to compete with HK for binding PK in a cell-free system. D567-T591, a 25-residue peptide which contains sufficient structural information for binding kallikrein in solution, blocked the binding of kallikrein to HK bound to endothelial cells and inhibited PK activation to kallikrein and the generation of kallikrein-activated urokinase on endothelial cell surfaces. HK-derived peptides could modulate excessive fibrinolysis and hypotension in sepsis and multiple trauma.

Conformational analysis of synthetic peptides encompassing the factor XI and prekallikrein overlapping binding domains of high molecular weight kininogen

High molecular weight kininogen, a plasma glycoprotein, circulates as a noncovalent complex with either prekallikrein or factor XI, two other plasma glycoproteins. The binding domain for factor XI within kininogen, Pro556-Met613 (58 residues), wholly contains the binding domain for prekallikrein, Ser565-Lys595 (31 residues), but Trp569-Lys595 (27 residues) retains some ability to bind prekallikrein. Complex formation between these proteins is mediated by recognition between complementary domains. The 58-residue factor XI peptide domain has now been prepared following a strategy of condensation of long-chain peptide fragments prepared using orthogonal chemistry protocols. The 58-, 31-, and 27-residue peptides assume very different structures in aqueous solution as revealed by differential scanning calorimetry, intrinsic fluorescence emission, and circular dichroism spectroscopies. Thus, the 31-residue peptide shows a broad endothermic transition in differential scanning calorimetry (DSC), but the 58-mer undergoes a well-defined, two-state transition (Tm 43 degrees C; transition enthalpy approximately 30 kcal/mol). The 58- and 27-residue peptides continuously lose structure with increasing temperature, but the 31-mer retains significant structure even at temperatures approaching 90 degrees C. Lys595 plays a critical role in maintaining structure through electrostatic contacts, probably with Asp572 in the N-terminal segment of the 31-residue sequence. Isothermal ligand titration calorimetry was used to directly assess the ability of the 31-, 27-, and 58-residue peptides to bind prekallikrein. The 31-residue peptide binds prekallikrein with 25-fold higher affinity (Kd = 1.0 x 10(-6) M) than the 58-residue peptide and with 5.4-fold higher affinity than the 27-residue peptide. Hence, the essential features of the 31-residue peptide domain required for binding prekallikrein are absent in the 58-residue peptide, which is optimized for binding factor XI. The results suggest that a conformational change may occur within kininogen that causes expression of one domain structure in preference to the other.

Potential role of two novel elastase-like enzymes in processing pro-transforming growth factor-alpha

Transforming growth factor-alpha (TGF-alpha) is a mitogenic peptide produced by tumor cells and by virally and chemically transformed cells in culture. TGF-alpha is almost certainly derived from its precursor protein (pro-TGF-alpha) by limited proteolysis, but the physiologically relevant processing enzyme(s) is(are) unknown. We now report that oncogenically transformed rat liver epithelial cells (known to secrete TGF-alpha) and Schwann cells in culture transfected with SV40 T-antigen (which are now reported to express mRNA encoding pro-TGF-alpha) contain membrane associated, neutral pH, serine proteinases which are elastase-like in their substrate specificity, but elastase is not known to be associated with these cell types. In both cell types, the enzyme is associated with a subcellular fraction enriched for microsomes and plasma membranes. Furthermore, the enzyme appears to be specifically induced 4-fold in the transformed epithelial cells as compared with the level of enzyme present in the nontransformed parental cells. The enzymes have been purified approximately 20,000-fold to near homogeneity (50-60 units/mg) and are virtually identical with regard to their molecular weights (38,000) and other physiochemical properties. Results obtained with numerous synthetic peptide substrates show the enzymes prefer nonpolar residues such as Ala and Val in the P1 and P2 positions, but promiscuity of cleavage specificity observed with long-chain peptide substrates is attributed to the absence of structure in these peptides. Thus, although these enzymes may be involved in processing pro-TGF-alpha at the plasma membrane of the cell, it is just as likely that these enzymes play other physiological roles in the parental and/or transformed cells and that there is no specific endoproteolytic processing enzyme of pro-TGF-alpha.

Design and synthesis of a helix heparin-binding peptide

Elaboration of heparin-protein-binding interactions is necessary to understand how heparin modulates protein function. The heparin-binding domain of some proteins is postulated to be a helix structure which presents a surface of high positive charge density. Thus, a synthetic 19-residue peptide designed to be alpha-helical in character was synthesized, and its interaction with heparin was studied. The peptide was shown to be 75% helix by circular dichroism (CD) spectrometry in neutral pH buffer (at 2 degrees C); helicity increased to nearly 85% under high ionic strength conditions or to nearly 100% in 75% ethanol. Increasing the temperature of the solution caused a change in the spectral envelope consistent with a coil transition of the peptide. The midpoint of the transition (i.e., the temperature at which the helix content was determined to be 50%) was 25 degrees C, and the determined van't Hoff enthalpy change (delta HvH) was 3.2 kcal/mol of peptide. By CD, heparin increases the helix content of the peptide to 100% and increases the apparent thermal stability of the peptide by about 1 kcal/mol. The melting point for the helix/coil transition of the heparin-peptide complex was 50 degrees C. The thermal coefficient of the transition (approximately 300 deg.cm2.dmol-1.degree C-1) was essentially the same for the peptide alone or the peptide-heparin complex. Dissociation of the complex under high ionic strength conditions was also observed in the CD experiment. Biological assays showed less heparin-binding activity than expected (micromolar KD values), but this was attributed to the absence of critical lysyl residues in the peptide.(ABSTRACT TRUNCATED AT 250 WORDS)