Urea unfolding of peptide helices as a model for interpreting protein unfolding

To provide a model system for understanding how the unfolding of protein alpha-helices by urea contributes to protein denaturation, urea unfolding was measured for a homologous series of helical peptides with the repeating sequence Ala-Glu-Ala-Ala-Lys-Ala and chain lengths varying from 14 to 50 residues. The dependence of the helix propagation parameter of the Zimm-Bragg model for helix-coil transition theory (s) on urea molarity ([urea]) was determined at 0 degree C with data for the entire set of peptides, and a linear dependence of In s on [urea] was found. The results were fitted by the binding-site model and by the solvent-exchange model for the interaction of urea with the peptides. Each of these thermodynamic models is able to describe the data quite well and we are not able to discern any difference between the ability of each model to fit the data. Thus a linear relation, ln s = ln s0 - (m/RT).[urea], fits the data for alpha-helix unfolding, just as others have found for protein unfolding. When the m value determined here for alpha-helix unfolding is multiplied by the number of helical residues in partly helical protein molecules, the resulting values agree within a factor of 2 with observed m values for these proteins. This result indicates that the interaction between urea and peptide groups accounts for a major part of the denaturing action of urea on proteins, as predicted earlier by some model studies with small molecules.

Bradykinin antagonists: development and applications

Bradykinin (BK) is involved in regulation of every major physiological system and is an initiator or mediator of many pathophysiological conditions. Rapid progress in understanding these aspects of BK biology has come since the discovery of BK antagonists. This article reviews principal points in the history of the kallikrein-kinin field and of kinin biology. The chemistry and development of antagonists for B1 and B2 kinin receptors is discussed. Uses of the antagonists in biomedical research and potential clinical applications are presented.

Role of EDRF in the regulation of shear rate in large coronary arteries in conscious dogs

To determine whether dilation of large coronary arteries normalizes shear during increased flow following brief occlusion, six dogs were instrumented to measure aortic and left ventricular pressures, left circumflex coronary artery external diameter, and coronary blood flow. The coronary artery was occluded for 15 or 30 s. Data were obtained before and after blockade of EDRF synthesis with nitro-L-arginine. Internal coronary artery diameter and wall shear were calculated on a moment-to-moment basis and the area under the flow curve was measured. Peak flow and shear rate were unaffected by NLA or by the occlusion duration. Flow curve area increased with the duration of occlusion. Internal and external diameters increased significantly for 15 s occlusions before NLA (by 4 +/- 1% in external diameter and by 11 +/- 4% in internal diameter) and for 30 s occlusions before NLA (by 5 +/- 1% in external diameter and by 14 +/- 5% in internal diameter) but not after NLA. Adenosine infusions of 0.05, 0.10, 0.50, and 1.0 mumol/kg/min were also used to dilate the coronary arteries. With each infusion, flow, shear and diameter were allowed to reach steady state. Steady state shear was reduced only slightly and did not approach the baseline state. We conclude that increased shear rate causes an increase in coronary artery diameter which is EDRF dependent. Increased coronary artery diameter during reactive hyperemia and adenosine infusions did not normalize wall shear.

Insulin-like growth factor-I and insulin stimulate the synthesis of IGF-binding protein-2 in a human embryonic kidney cell line

Insulin and insulin-like growth factor (IGF)-I are thought to be major metabolic regulators of IGF-binding protein-2 (IGFBP-2). We have examined the regulation of IGFBP-2 expression by IGF-I and insulin in 293 cells, a cell line derived from human embryonic kidney. The predominant 34 kDa IGFBP in media conditioned by unstimulated 293 cells was identified as IGFBP-2 by immunoprecipitation. IGFBP-2 levels were increased 6 to 7-fold following incubation with IGF-I, IGF-II or insulin for 48 h. A corresponding increase in IGFBP-2 mRNA was not observed, suggesting that regulation occurred at the translational or post-translational level. The stimulation of IGFBP-2 by IGF-I and insulin was reversibly abolished by incubation with protein synthesis inhibitors such as cycloheximide. Biosynthetic labeling of quiescent 293 cells using [35S]cysteine indicated that incubation with insulin or IGF-I for 24 h increased the synthesis of total cell proteins (predominantly intracellular) and IGFBP-2 (predominantly secreted) to a similar extent (2- to 4-fold). These results suggest that the increase in IGFBP-2 secreted by 293 cells after incubation with IGF-I or insulin largely results from a general stimulation of protein synthesis.

The present and future of bradykinin antagonists

It is now just a decade since the first evidence was obtained for bradykinin antagonists effective on most systems (B2 antagonists). During that decade antagonists have been used to elucidate roles for kinins in physiology and pathophysiology, and are now in clinical trials. Some of these developments, as well as prospects for future developments, are reviewed.

Helix-forming tendencies of amino acids in short (hydroxybutyl)-L-glutamine peptides: an evaluation of the contradictory results from host-guest studies and short alanine-based peptides

The helix propensities ("s-values") of amino acids measured using short alanine-based peptides are different, in both magnitude and rank order, from those found using random sequence copolymers of a "guest" amino acid and a (hydroxyalkyl)-L-glutamine "host". The origin of these differences is investigated here. In short alanine-based peptides containing 1-5 (hydroxybutyl)-, (hydroxypropyl)-, or (hydroxyethyl)-L-glutamines (HBQ, HPQ, and HEQ, respectively), we find the rank order of helix propensities to be Ala > HBQ > HPQ > HEQ, which is consistent with earlier results for HBQ, HPQ, and HEQ homopolymers and is attributed to helix-stabilizing hydrophobic interactions [Lotan, N., Yaron, A., & Berger, A. (1966) Biopolymers 4, 365-368]. The apparent s-values of nonpolar amino acids in a 17-residue, HBQ-based peptide cluster around 1, as they do in the host-guest studies, but in contrast to results with alanine-based peptides. The differences between the host-guest results and results obtained using alanine-based peptides may be rationalized in terms of side-chain interactions involving the hydroxyalkyl moiety.

Role of EDRF in the regulation of regional blood flow and vascular resistance at rest and during exercise in conscious dogs

The contribution of endothelium-derived relaxing factor (EDRF) to the regulation of regional vascular resistance and tissue blood flow at rest and during acute moderate exercise was studied in chronically instrumented conscious dogs. Radioactive microspheres were injected before and during exercise to measure regional blood flow. An infusion of nitro-L-arginine (L-NA), an analogue of L-arginine, was used to inhibit the synthesis of EDRF and resulted in a significant increase in mean arterial pressure, associated with significantly elevated vascular resistance in heart, skeletal muscle, renal and splanchnic circulations and with decreases in tissue blood flow in those regions at rest. Acute exercise caused a typical redistribution of blood flow, in which there was vasodilation in heart and working skeletal muscles, accompanied by vasoconstriction in kidney and splanchnic circulations. L-NA resulted in significantly elevated vascular resistance during vasodilation in heart and working skeletal muscles and also significantly increased vasoconstriction in renal cortex, stomach, pancreas, liver, and colon during exercise. Blood flows during exercise were largely unaffected by L-NA treatment. Our results suggest that whereas EDRF functions to regulate basal vascular tone and vascular resistance during exercise, EDRF has a minor role in determining the pattern of the redistribution of tissue blood flow during exercise.

A CD and an NMR study of multiple bradykinin conformations in aqueous trifluoroethanol solutions

CD and nmr studies have been carried out on aqueous trifluoroethanol (TFE) solutions of bradykinin (BK) and a bradykinin antagonist. The CD results exhibit a striking effect of TFE on the spectra of BK, with sequence Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg, and the BK antagonist, with sequence D-Arg-Arg-Pro-Hyp-Gly-Thi-D-Ser-D-Cpg-Cpg-Arg [where Hyp is 4-hydroxy-L-proline; Thi refers to beta-(2-thienyl)-L-alanine and Cpg refers to alpha-cyclopentylglycine). The effect of increasing concentration of TFE in water on the difference ellipticity at 222 nm was examined and showed that BK may be a mixture of at least two different conformers, one of which largely forms when the TFE concentration is increased beyond 80%. The linear extrapolation of 100% of the difference ellipticity of BK at low TFE concentrations yields a value in agreement with that shown by the BK antagonist, indicating that the conformation of BK at the lower TFE concentrations is similar to that of the BK antagonist. The conformational analysis was carried out using both one-dimensional and two-dimensional 1H-nmr techniques. The total correlation spectroscopy (TOCSY) spectrum of BK in a 60/40% (v/v) TFE/H2O solution at 10 degrees C and a nuclear Overhauser effect spectroscopy (NOESY) spectrum that shows only sequential H alpha (i)-NH(i + 1) or the H alpha (i)-H delta delta' (i + 1) NOEs indicate that the majority of the molecules adopt an all-trans extended conformation. The TOCSY for BK in the 95/5% (v/v) TFE/H2O solution shows that there are two major conformations in the solution with about equal population. The NOESY experiment shows two new important cross peaks for one conformation, namely Pro2 (alpha)-Pro3 (alpha) and the Pro2 (alpha)-Gly4(NH), indicating a cis Pro2-Pro3 bond and a type VI beta-turn between residues Arg1 and Gly4 involving cis proline at position 3, respectively. The low temperature coefficient of Gly4 for this conformation suggests the presence of an intramolecular hydrogen bond, therefore a type VIa beta-turn is present. The other conformation is all trans and extended. The BK antagonist shows difference CD spectra in TFE solutions referred to H2O that are superficially indicative of a beta-bend.(ABSTRACT TRUNCATED AT 400 WORDS)

Studies on chymotrypsin-like catalysis by synthetic peptides

The synthetic peptide Chymohelizyme-1 (CHZ-1) exhibits esterase activity against carbobenzoxytyrosine p-nitrophenyl ester (ZTONP), carbobenzoxyalanine p-nitrophenyl ester (ZAONP), and t-butyloxy-carbonyltyrosine p-nitrophenyl ester (BocTONP). However, earlier reports of catalytic activity against less labile esters and amides have proven to be incorrect. The major reason for the errors appears to have been the omission of certain controls in the previous work. Although the catalytic triad does not appear to be functioning as designed, the catalytic activity of CHZ-1 does depend on the integrity of its primary structure. The pH dependence of hydrolysis of ZTONP points to general-base catalysis, whereas a preference for hydrophobic substrates suggest that the structure of CHZ-1 is performing some other role in assisting catalysis.

Low-density lipoprotein particle size in type 2 diabetic patients and age matched controls

Non-enzymatic glycation of low-density lipoprotein (LDL), and the predominance of small dense LDL particles may together contribute to the increased risk of atherosclerosis in diabetes. We aimed to establish whether the size of LDL particles is related to plasma triglyceride concentration, and to the extent of LDL glycation in type 2 diabetic patients. Sixteen men with type 2 diabetes and 16 age matched non-diabetic controls were studied. LDL size was measured by rapid density gradient ultracentrifugation, and LDL glycation by affinity chromatography. Modal LDL density correlated with plasma triglyceride concentrations in both diabetic and control groups (r = 0.86, P < 0.0001, and r = 0.76, P < 0.0008, respectively). There was no significant difference in these variables between the groups. LDL modal density showed no correlation with HbA1, serum fructosamine or plasma glucose in either group. In the diabetic group the degree of LDL glycation correlated with serum fructosamine (r = 0.74, P < 0.001), HbA1 (r = 0.65, P < 0.008), and with plasma glucose (r = 0.64, P < 0.008). Our results suggest that, in well controlled type 2 diabetic patients LDL size is independent of short-term glycaemic control but can be predicted by plasma triglyceride concentrations.

Is bradykinin (BK) a physiological vasodilator in the gut?

The physiological role of bradykinin (BK) as a mesenteric vasoregulator was explored. This nonapeptide is a potent vasodilator substance when administered exogenously in multiple in vivo models and is a smooth muscle relaxant when added to in vitro preparations. BK is naturally occurring in the gut wall. The substrate for BK, as well as the biosynthetic and metabolizing systems are present in the blood, the vascular wall, immunological cells, and perivascular neurons. BK B2 and B1 receptors have been characterized with sympathetic agonist and antagonist substances, and the receptors are present on mesenteric endothelial cells and myocytes. BK interacts with multiple endogenous mesenteric vasodilator mediators, such as nitric oxide, prostacyclin, and neuropeptides. Taken together this evidence supports the functional importance of BK as a normal vasodilator in the gut.

Characterization of receptor-mediated actions of T-kinin

T-Kinin (Ile-Ser-bradykinin) is unique to the rat. This study characterizes the receptors involved in T-kinin activity on both the intact isolated rat uterus and membrane receptor preparations of the rat uterus. The results show that T-kinin acts through kinin B2 receptors in the rat uterus as demonstrated by B2 receptor-antagonist inhibition. While the potency of T-kinin on rat uterus contraction was similar to that of bradykinin, binding studies showed that the affinity of T-kinin to the receptor was 10-fold lower than that of bradykinin. On the other hand, the D isomer of T-kinin, D-Ile-Ser-bradykinin, had an affinity for the receptor greater than that of T-kinin and was more potent in causing contraction. Comparing this finding with our previously published report that D-Ile-Ser-bradykinin is not active on the kinin receptor for vascular permeability indicates that the kinin receptors in the rat uterus are not the same as those previously reported in the smooth muscle of the vasculature, i.e. there exists subclasses of kinin B2 receptors. The data from binding studies on a variety of T-kinin analogues show that the substitution of hydroxyproline (Hyp) for Pro5, together with the D-configuration at Ile1 and/or Ser2 may be useful for the development of selective T-kinin antagonists. Studies involving pretreatment of the tissue with indomethacin demonstrated that prostaglandin release was more of a component of T-kinin's activity on the rat uterus than that of bradykinin.

The aggregation properties of some bradykinin analogs

Bradykinin (BK) is a peptide hormone with sequence Arg1-Pro2-Pro3-Gly4-Phe5-Ser6-Pro7-Phe8-Arg9 and has been implicated in a multitude of pathophysiological processes such as the ability to lower systemic blood pressure and stimulate pain. Bulky, beta-branched D-aliphatic residues at position 7 combined with bulky L-aliphatic residues at position 8 have now been observed to yield strong antagonists. Nuclear magnetic resonance studies have been carried out on many of these molecules with a view to determining their solution conformations. However, two such analogs, namely DArg-[Hyp3, Thi5, DSer6, DCpg7, Cpg8]-BK [I] and DArg-[Hyp3, DSer6, DCpg7, Cpg8]-BK [II] (Cpg = alpha-cyclopentyl-glycine; Hyp = 4-hydroxy-L-proline, Thi = beta-(2-thienyl)-L-alanine), have exhibited an abnormal, non-linear temperature dependence for the amide NH proton of Cpg8. The NH of Arg9 also shows a slightly non-linear temperature dependence at higher temperatures above 25 degrees C. In addition, a very slow exchange rate for the NH protons of DCpg7, Cpg8 and Arg9 indicated aggregation of these two analogs, which was confirmed using the circular dichroism experiments.

Synthesis and stability of 3-nitro-2-pyridinesulfenyl chloride (NpysCl)

3-Nitro-2-pyridinesulfenyl chloride (NpysCl) is the starting material for the synthesis of N-, O- and S-Npys-protected amino acids. Two efficient, novel synthetic routes to NpysCl are described. The stability of NpysCl was determined in a variety of solvents, with and without base, to determine the most suitable solvent and base for the synthesis of N-Npys amino acids. The syntheses of Npys-Ala and Boc-Lys(Npys) tert-butylammonium salt are also described.

Proton magnetic resonance studies of bradykinin antagonists

Bradykinin (BK) is a peptide hormone with sequence Arg1-Pro2-Pro3-Gly4-Phe5-Ser6-Pro7-Phe8-Arg9 and has been implicated in a multitude of pathophysiological processes such as the ability to lower systemic blood pressure and stimulate pain. BK analogues having bulky, beta-branched D-aliphatic residues at position 7 combined with bulky L-aliphatic residues at position 8 have now been observed to be strong antagonists. Conformational studies based on two-dimensional nmr experiments in methanol/water (80/20 v/v) were carried out on several such active antagonists in a polar solvent. Included in this study were the very active antagonists, [D-Arg0,Hyp3,Thi5,D-Cpg7,Cpg8]-BK [Cpg: alpha-cyclo-pentyl-glycine; Hyp: trans-4-hydroxy-L-proline; Thi: beta-(2-thienyl)-L-alanine] (I), [D-Arg0,Hyp3,D-Cpg7,Cpg8]-BK (II), as well as its variant with D-Cpg7 replaced by Cpg7, namely [D-Arg0,Hyp3,Cpg7,Cpg8]-BK (III). A turn-like structure, which coexists with the extended conformation, was observed between residues 2 and 5 for the most active antagonists I and II, in direct correlation with the peptide activities. No turn-like structure was found for residues 6-9. In peptide III, a turn-like structure was not identified. The existence of a turn at the C-terminal end of bradykinin and its analogues has been predicted by empirical calculations and supported by nmr measurements. But the present nmr study on the most active antagonists (I, II) does not support this hypothesis. Instead, the data suggest that a turn-like structure between residues 2 and 5 could be important for antagonist activity. Finally, one weak inhibitor [D-Cpg7]-BK (IV) showed no defined secondary structure.

A proton magnetic resonance study of two synthetic agonist-antagonist pairs of bradykinin analogues

The conformation of two agonist-antagonist pairs of bradykinin (Arg1-Pro2-Pro2-Gly4-Phe5-Ser6-Pro7-Phe8-Arg9) analogues were studied in CD3OH/H2O solution by 1H-nmr techniques. The first agonist peptide studied, D-Arg0-Arg1-Pro2-Hyp3-Gly4-Thi5-Ser6-Pro7- Thi8-Arg9, differs from the bradykinin sequence by the addition of D-Arg0, the replacement of the Phe moieties in positions 5 and 8 by Thi (Thi = beta-(2-thienyl)-L-alanine), and Hyp3 (Hyp = L-4-hydroxy-L-proline) in position 3. In the corresponding antagonist sequence, Pro7 is replaced by D-Phe7. The second agonist-antagonist pair studied does not contain the D-Arg0 residue, which is present only to slow down the rate of metabolism. Based on complete resonance assignments from two-dimensional total correlation spectroscopy and rotating frame nuclear Overhauser effect spectroscopy spectra at 500 MHz, the peptides were analyzed in terms of intraresidue, sequential, and medium-range nuclear Overhauser effects, amide proton temperature coefficients, and vicinal coupling constants. Both agonist peptides show clear evidence for the existence of a type I beta-turn comprising the C-terminal residues Ser6-Pro7-Thi8-Arg9 in fast conformational equilibrium with extended structures throughout. Although the conformational space is dominated by extended structures, the presence of the beta-turn is spectroscopically clearly discernible. The two antagonist peptides, on the other hand, do not show evidence of turn formation but rather the presence of an extended conformation with some irregularities in the N-terminal region of the peptide. While the existence of a turn at the C-terminal end of bradykinin and its analogues with agonist activity has been predicted by empirical calculations and measurements in very apolar solvents, this study, for the first time, provides evidence based on physical data in a polar solvent environment that the turn is present, that it is type I and that it is essential for agonist activity. In the particular solvent used in these studies, the Pro7 to D-Phe7 substitution precluded the formation of the turn for the C-terminal residues of the antagonist.

Telephone-Assessed Mental State

In 30 patients with Alzheimer's disease (AD), we compared performance on a brief Telephone-Assessed Mental State (TAMS) examination with performance on standard cognitive instruments administered face to face. TAMS scores correlated strongly with scores on both the Mini Mental State Examination (rho = 0.81) and the Alzheimer's Disease Assessment Scale (rho = -0.80).

Bradykinin-induced mesenteric vasodilation is mediated by B2-subtype receptors and nitric oxide

We investigated mechanisms mediating bradykinin (BK)-induced anterior mesenteric artery (AMA) vasodilation in anesthetized rats. The velocity of blood flowing (VBF) in the AMA was measured with pulsed Doppler velocimetry, and arterial pressure (BP) was measured with a pressure transducer. Drugs were infused through an intra-aortic catheter positioned proximal to the AMA origin. AMA conductance (C) was calculated from mean VBF/BP and expressed as percent of control C. BK infusion (10-1,000 ng.kg-1.min-1) increased C significantly (Cmax = 201 +/- 18%, ED50 = 100 ng.kg-1.min-1, P < 0.01 for all doses). A B2-subtype receptor antagonist, D-Arg,[Hyp3,Thi5.8,D-Phe7]BK, administered at 10(5) ng.kg-1.min-1 before or during BK infusion, inhibited the vasodilation by 73 +/- 7 and 103 +/- 7%, respectively. A nitric oxide (NO) synthesis inhibitor, NG-nitro-L-arginine, administered at 5.0 mg/kg 15 min before BK, inhibited the hyperemia by 61 +/- 8%. Neither a B1-receptor antagonist nor intrajejunal capsaicin inhibited BK-induced vasodilation. BK-evoked, dose-dependent, mesenteric vasodilation in rats appears to be mediated partly by B2-receptors and endogenous NO generation.

Congenital conductive hearing loss: the need for early identification and intervention

Pediatricians are familiar with conductive hearing loss, but to many it is synonymous with otitis media of some type. There is a group of children who have anatomic abnormalities of the external or middle ear causing their hearing losses. The records of 565 hearing-impaired children were reviewed, and 54 with non-otitis-related conductive hearing loss were found. Date of birth, degree of loss, diagnosis or presence of any associated abnormalities, and ages of confirmation and intervention were studied. There were 22 children with microtia, 14 with abnormalities of the external auditory canal and normal pinnae, 15 with obvious dysmorphic features including 9 who had syndromes well known to be associated with hearing abnormalities, and only 3 who had isolated hearing loss. Despite all these clues, hearing loss was diagnosed in only 10 children (excluding those with bilateral microtia) before 12 months of age although their average hearing loss was 45 dB. It is important for the primary care provider to recognize these children as early as possible as their loss is permanent and almost always more severe than that seen in otitis.

Neuropeptide processing in pathophysiology

Neuropeptides (peptides synthesized and secreted by neurons) perform many functions in the central nervous system as neurotransmitters, neuromodulators and neurotrophic factors. Neuropeptides are important regulators of amine neurotransmitter release, and can be identified as playing important roles in several pathological states. Neuropeptides are synthesized as protein precursors that are processed enzymatically to yield the biologically active peptides. Many neuropeptides having defined roles are further processed enzymatically to yield fragments having totally different actions. Examples discussed are substance P, adrenocorticotrophic hormone, endorphins and vasopressin.