Treatment of functional gastrointestinal disorders with antidepressant medications: a meta-analysis

BACKGROUND

Functional gastrointestinal disorders are common, accounting for up to 50% of gastroenterology referrals, and several randomized controlled trials have evaluated antidepressant therapy for their treatment.

METHODS

We performed a meta-analysis of published, English-language, randomized clinical trials on the use of antidepressants for the treatment of patients with functional gastrointestinal disorders.

RESULTS

Twelve randomized placebo-controlled trials of antidepressant treatment of functional gastrointestinal disorders were identified. One was excluded for using a combination of a tricyclic and neuroleptic agent. The medications included tricyclic antidepressants (amitriptyline [n = 3], clomipramine [n = 1], desipramine [n = 2], doxepin [n = 1], and trimipramine [n = 2]), and the antiserotonin agent, mianserin (n = 2). In addition, one trial compared two different antidepressants (mianserin and clomipramine) with placebo. Data were abstracted for the dichotomous outcome of symptom improvement in seven studies, and for the continuous variable of pain score in eight studies. The summary odds ratio for improvement with antidepressant therapy was 4.2 (95% confidence interval [CI]: 2.3 to 7.9), and the average standardized mean improvement in pain was equal to 0.9 SD units (95% CI: 0.6 to 1.2 SD units). On average 3.2 patients needed to be treated (95% CI: 2.1 to 6.5 patients) to improve 1 patient's symptom.

CONCLUSION

Treatment of functional gastrointestinal disorders with antidepressants appears to be effective. Whether this improvement is independent of an effect of treatment on depression needs further evaluation.

Treatment of fibromyalgia with antidepressants: a meta-analysis

BACKGROUND

Fibromyalgia is a common, poorly understood musculoskeletal pain syndrome with limited therapeutic options.

OBJECTIVE

To systematically review the efficacy of antidepressants in the treatment of fibromyalgia and examine whether this effect was independent of depression.

DESIGN

Meta-analysis of English-language, randomized, placebo-controlled trials. Studies were obtained from searching MEDLINE, EMBASE, and PSYCLIT (1966-1999), the Cochrane Library, unpublished literature, and bibliographies. We performed independent duplicate review of each study for both inclusion and data extraction.

MAIN RESULTS

Sixteen randomized, placebo-controlled trials were identified, of which 13 were appropriate for data extraction. There were 3 classes of antidepressants evaluated: tricyclics (9 trials), selective serotonin reuptake inhibitors (3 trials), and S-adenosylmethionine (2 trials). Overall, the quality of the studies was good (mean score 5.6, scale 0-8). The odds ratio for improvement with therapy was 4.2 (95% confidence interval [95% CI], 2.6 to 6.8). The pooled risk difference for these studies was 0.25 (95% CI, 0.16 to 0.34), which calculates to 4 (95% CI, 2.9 to 6.3) individuals needing treatment for 1 patient to experience symptom improvement. When the effect on individual symptoms was combined, antidepressants improved sleep, fatigue, pain, and well-being, but not trigger points. In the 5 studies where there was adequate assessment for an effect independent of depression, only 1 study found a correlation between symptom improvement and depression scores. Outcomes were not affected by class of agent or quality score using meta-regression.

CONCLUSION

Antidepressants are efficacious in treating many of the symptoms of fibromyalgia. Patients were more than 4 times as likely to report overall improvement, and reported moderate reductions in individual symptoms, particularly pain. Whether this effect is independent of depression needs further study.

The validity and accuracy of the Work Productivity and Activity Impairment questionnaire--irritable bowel syndrome version (WPAI:IBS)

BACKGROUND

Irritable bowel syndrome is a common chronic functional gastrointestinal disorder characterized by recurrent abdominal pain and discomfort associated with alterations in bowel habit. Irritable bowel syndrome affects patients' quality of life and increases productivity loss.

AIM

To assess validity and accuracy of the Work Productivity and Activity Impairment questionnaire in irritable bowel syndrome as a tool for quantifying the effects of irritable bowel syndrome on productivity and daily activities.

METHODS

Validity and accuracy were evaluated in 135 irritable bowel syndrome patients relative to three measures of irritable bowel syndrome disease severity; a debriefing questionnaire; retrospective diary; Work Limitations Questionnaire, and an activity impairment measure (Dimensions of Daily Activities).

RESULTS

Symptom severity scores, diary scores, Work Limitations Questionnaire and Dimensions of Daily Activities were significant predictors of work productivity and activity impairment questionnaire in irritable bowel syndrome measures of work time missed, and work and activity productivity loss (P = 0.04 to < 0.0001). Impairment due to irritable bowel syndrome was estimated to be 2.9-4.3% for work time missed and 22-32% for impairment at work, the equivalent of 9.7 -14 h lost productivity per week. Activity impairment was 24-41%.

CONCLUSIONS

Discriminative validity of the Work Productivity and Activity Impairment questionnaire in irritable bowel syndrome was established, making it the only validated tool for measuring the relative differences between disease severity groups and quantifying work productivity loss and activity impairment in irritable bowel syndrome patients.

NMR solution structure of the isolated N-terminal fragment of protein-G B1 domain. Evidence of trifluoroethanol induced native-like beta-hairpin formation

The solution structure of the isolated N-terminal fragment of streptococcal protein-G B1 domain has been investigated in H2O and TFE/H2O solution by CD and NMR to gain insight into the possible role that native beta-hairpin secondary structure elements may have in early protein folding steps. The fragment also has been studied under denaturing conditions (6 M urea), and the resulting NMR chemical shifts were used as a reference for the disordered state. On the basis of CD and NMR data, it is concluded that in aqueous solution the fragment is basically flexible, with two local low populated chain bends involving residues 8-9 and 14-15, respectively, in close agreement with secondary structure predictions, a structure that is different from the final folded state of that segment of the protein. The changes in the CD spectrum, the presence of several medium-range NOEs plus two long-range NOEs, and the sign of the H alpha conformational shifts reveal that the addition of TFE facilitates the formation of a set of transient beta-hairpins involving essentially the same residues that form the native beta-hairpin found in the final three-dimensional structure of the B1 domain. The stabilization of native-like structures by TFE is known to occur for helices, but, to our knowledge, this is the first time the stabilization of a native-like beta-hairpin structure by TFE is reported. Since long-range tertiary interactions are absent in the isolated fragment, our results support the idea that, in addition to helices, beta-hairpins may play an active role in directing the protein folding process.

Solution structure of gamma 1-H and gamma 1-P thionins from barley and wheat endosperm determined by 1H-NMR: a structural motif common to toxic arthropod proteins

The complete assignment of the proton NMR spectra of the homologous gamma 1-hordothionin and gamma 1-purothionin (47 amino acids, 4 disulfide bridges) from barley and wheat, respectively, has been performed by two-dimensional sequence-specific methods. A total of 299 proton-proton distance constraints for gamma 1-H and 285 for gamma 1-P derived from NOESY spectra have been used to calculate the three-dimensional solution structures. Initial structures have been generated by distance geometry methods and further refined by dynamical simulated annealing calculations. Both proteins show identical secondary and tertiary structure with a well-defined triple-stranded antiparallel beta-sheet (residues 1-6, 31-34, and 39-47), an alpha-helix (residues 16-28), and the corresponding connecting loops. Three disulfide bridges are located in the hydrophobic core holding together the alpha-helix and the beta-sheet and forming a cysteine-stabilized alpha-helical (CSH) motif. Moreover, a clustering of positive charges is observed on the face of the beta-sheet opposite to the helix. The three-dimensional structures of the gamma-thionins differ remarkably from plant alpha- and beta-thionins and crambin. However, they show a higher structural analogy with scorpion toxins and insect defensins which also present the CSH motif.

High-resolution three-dimensional structure of ribonuclease A in solution by nuclear magnetic resonance spectroscopy

High-resolution three-dimensional structures of bovine pancreatic ribonuclease A in aqueous solution have been determined by nuclear magnetic resonance (NMR) spectroscopy combined with restrained molecular dynamics calculations. The structures are based on: (1) 464 interproton distance constraints with accurate upper and lower limits, determined from build-up rates of nuclear Overhauser effects (NOE) by using the complete relaxation matrix; (2) 999 more approximate upper limits for interproton distances; and (3) 42 dihedral angle constraints (37 for phi and 5 for chi 1). A total of 16 structures were calculated, which show a root-mean-square (r.m.s.) deviation of 0.66 A for the backbone atoms and 1.68 A for all heavy-atoms. The converged structures are highly similar to those found in the crystal state. r.m.s. deviation of backbone atom positions in the crystal as compared to those in the average solution structure is 0.92 A. Observed differences are concentrated in loop regions and in the neighborhood of His119 and His48 side-chains. Dynamic aspects, such as H/D amide proton exchange and side-chain mobility have been examined.

De novo design of a monomeric three-stranded antiparallel beta-sheet

Here we describe the NMR conformational study of a 20-residue linear peptide designed to fold into a monomeric three-stranded antiparallel beta-sheet in aqueous solution. Experimental and statistical data on amino acid beta-turn and beta-sheet propensities, cross-strand side-chain interactions, solubility criteria, and our previous experience with beta-hairpins were considered for a rational selection of the peptide sequence. Sedimentation equilibrium measurements and NMR dilution experiments provide evidence that the peptide is monomeric. Analysis of 1H and 13C-NMR parameters of the peptide, in particular NOEs and chemical shifts, and comparison with data obtained for two 12-residue peptides encompassing the N- and C-segments of the designed sequence indicates that the 20-residue peptide folds into the expected conformation. Assuming a two-state model, the exchange kinetics between the beta-sheet and the unfolded peptide molecules is in a suitable range to estimate the folding rate on the basis of the NMR linewidths of several resonances. The time constant for the coil-beta-sheet transition is of the order of several microseconds in the designed peptide. Future designs based on this peptide system are expected to contribute greatly to our knowledge of the many factors involved in beta-sheet formation and stability.

1H NMR detection of cerebral myo-inositol

A previously unassigned group of prominent multiplets of the 360 MHz 1H NMR spectrum of acid stable metabolite extracts from rat brain is shown to arise from free myo-inositol. This conclusion is derived from a systematic analysis of the high-resolution 1H NMR spectra of brain acid extracts, in which appropriate conditions and optimal proton signals have been selected for the quantitative analysis of up to 15 metabolites. Developmental variations in the cerebral content of myo-inositol could be readily detected using this approach, which provides a novel alternative to study myo-inositol metabolism under physiological or pathological conditions.

1H NMR and CD evidence of the folding of the isolated ribonuclease 50-61 fragment

In our search for potential folding intermediates we have prepared and characterized the fragment of RNase A corresponding to residues 50-61. Proton chemical shift variations with temperature, addition of stabilizing (TFE) or denaturing agents (urea) provide a strong experimental basis for concluding that in aqueous solution this RNase fragment forms an alpha-helix structure similar to that in the intact RNase A crystal. This conclusion lends strong support to the idea that elements of secondary structure (mainly alpha-helices) can be formed in the absence of tertiary interactions and act as nucleation centers in the protein folding process.

NMR solution structure of the antifungal protein from Aspergillus giganteus: evidence for cysteine pairing isomerism

The solution structure of the antifungal protein (AFP, 51 residues, 4 disulfide bridges) from Aspergillus giganteus has been determined by using experimentally derived interproton distance constraints from nuclear magnetic resonance (NMR) spectroscopy. Complete sequence-specific proton assignments were obtained at pH 5.0 and 35 degrees C. A set of 834 upper limit distance constraints from nuclear Overhauser effect measurements was used as input for the calculation of structures with the program DIANA. An initial family of 40 structures calculated with no disulfide constraints was used to obtain information about the disulfide connectivities, which could not be determined by standard biochemical methods. Three possible disulfide patterns were selected and the corresponding disulfide constraints applied to generate a family of 20 DIANA conformers for each pattern. Following energy minimization, the average pairwise RMSD of the 20 conformers of each family is 1.01, 0.89, and 1.01 A for backbone atoms and 1.82, 1.74, and 1.81 A for all heavy atoms. One of these three families contains the disulfide bridge arrangement actually present in the solution structure of AFP. Although the three families fulfill the NMR constraints, one of the disulfide patterns considered (cysteine pairs 7-33, 14-40, 26-49, 28-51) is favored among the others on the basis of previous chemical studies. It thus probably corresponds to the actual pattern of disulfide bridges present in the protein, and the corresponding family represents the solution structure of AFP. The folding of AFP consists of five antiparallel beta strands connected in a -1, -1, +3, +1 topology and highly twisted, defining a small and compact beta barrel stabilized by four internal disulfide bridges. A cationic site formed by up to three lysine side chains adjacent to a hydrophobic stretch, both at the protein surface, may constitute a potential binding site for phospholipids which would be the basis of its biological function. On the other hand, a second, minor form of AFP has been detected. NMR data, together with results from mass spectrometry, chemical analysis, and sedimentation equilibrium, suggest that this species differs from the major form in the pairs of cysteines involved in the four disulfide bridges.

Sequential 1H-NMR assignment and solution structure of bovine pancreatic ribonuclease A

Assignments for 1H-NMR resonances of most of the residues of bovine pancreatic ribonuclease (RNase A) have been obtained by sequence-specific methods. Identification and classification of spin systems have been carried out by two-dimensional phase-sensitive correlated spectroscopy (360 MHz) and single relayed coherence transfer spectroscopy. Sequence-specific assignments have been achieved by phase-sensitive two-dimensional nuclear Overhauser effect spectroscopy. To overcome the problem of spectral overlap use has been made of (a) an exhaustive analysis of partly exchanged RNase A (spectra in D2O), (b) a comparison with the subtilisin-modified enzyme (RNase S) and (c) small spectral perturbations caused by changes in pH and temperature. The secondary structure elements have been identified from the observed sequential, medium and long-range nuclear Overhauser effects together with data from amide-exchange rates. All information collected leads to the conclusion that the crystal and the solution structures are closely similar.

Rat model of experimental endocarditis

A simple model of infective endocarditis was produced in rats. With the aid of a guide wire, polyethylene catheters were passed into the left ventricle through the right carotid artery of Sprague-Dawley rats weighing 300 to 350 g. A volume of 1 ml of an overnight culture of Streptococcus mitis, Staphylococcus aureus, or Streptococcus faecalis was intravenously injected 1 to 2 days after catheterization. Bacterial titers of Streptococcus mitis in vegetations were about 10(4)-fold greater than in other tissues. Blood cultures were always positive after 6 h. Mortality was 19% at 1 week and 82% at 2 weeks. Catheters were pulled 24 h after infection, and vegetation titers of greater than 7.0 log10 colony-forming units per g were sustained at 5 days. In intravenously infected rats without catheters, blood and tissues were sterile after 3 to 5 days. With Staphylococcus aureus, vegetations had greater than 9.0 log10 colony-forming units and with Streptococcus faecalis 8.8 +/- 0.3 log10 colony-forming units per g at 2 days. The rat model of infective endocarditis should prove to be suitable for further pathological and therapeutic studies.

Characterization of pKa values and titration shifts in the cytotoxic ribonuclease alpha-sarcin by NMR. Relationship between electrostatic interactions, structure, and catalytic function

The electrostatic behavior of titrating groups in alpha-sarcin was investigated using 1H NMR spectroscopy. A total of 209 chemical shift titration curves corresponding to different protons in the molecule were determined over the pH range of 3.0-8.5. Nonlinear least-squares fits of the data to simple relationships derived from the Henderson-Hasselbalch equation led to the unambiguous determination of pKa values for all glutamic acid and histidine residues, as well as for the C-terminal carboxylate and most of the aspartic acids in the free enzyme. The ionization constants of catalytically relevant histidines, His50 and His137, and glutamic acid, Glu96, in the alpha-sarcin-2'-GMP complex were also determined. The pKa values of 15 ionizable groups (C-carboxylate, six aspartic acids, four glutamic acids, and four histidines) were found to be close to their normal values. On the other hand, a number of side chain groups, including those in the active center, showed pKa values far from their intrinsic values. Thus, the pKa values for active site residues His50, Glu96, and His137 were 7.7, 5.2, and 5.8 in the free enzyme and 7.6, approximately 4.8, and 6.8 in the alpha-sarcin-2'-GMP complex, respectively. The pKa values and the activity profile against ApA, as a function of pH, are in agreement with the proposed enzymatic mechanism (in common with RNase T1 and the family of the microbial ribonucleases), in which Glu96 and His137 act as a general base and general acid, respectively. In almost all microbial ribonucleases, a Phe-His interaction is present, which affects the pKa of one of the His residues at the active site (His137). The absence of this interaction in alpha-sarcin would explain the lower pKa value of this His residue, and provides an explanation for the decreased RNase activity of this protein as compared to those of other microbial ribonucleases.

The highly refined solution structure of the cytotoxic ribonuclease alpha-sarcin reveals the structural requirements for substrate recognition and ribonucleolytic activity

alpha-Sarcin selectively cleaves a single phosphodiester bond in a universally conserved sequence of the major rRNA, that inactivates the ribosome. The elucidation of the three-dimensional solution structure of this 150 residue enzyme is a crucial step towards understanding alpha-sarcin's conformational stability, ribonucleolytic activity, and its exceptionally high level of specificity. Here, the solution structure has been determined on the basis of 2658 conformationally relevant distances restraints (including stereoespecific assignments) and 119 torsional angular restraints, by nuclear magnetic resonance spectroscopy methods. A total of 60 converged structures have been computed using the program DYANA. The 47 best DYANA structures, following restrained energy minimization by GROMOS, represent the solution structure of alpha-sarcin. The resulting average pairwise root-mean-square-deviation is 0.86 A for backbone atoms and 1.47 A for all heavy atoms. When the more variable regions are excluded from the analysis, the pairwise root-mean-square deviation drops to 0.50 A and 1.00 A, for backbone and heavy atoms, respectively. The alpha-sarcin structure is similar to that reported for restrictocin, although some differences are clearly evident, especially in the loop regions. The average rmsd between the structurally aligned backbones of the 47 final alpha-sarcin structures and the crystal structure of restrictocin is 1.46 A. On the basis of a docking model constructed with alpha-sarcin solution structure and the crystal structure of a 29-nt RNA containing the sarcin/ricin domain, the regions in the protein that could interact specifically with the substrate have been identified. The structural elements that account for the specificity of RNA recognition are located in two separate regions of the protein. One is composed by residues 51 to 55 and loop 5, and the other region, located more than 11 A away in the structure, is the positively charged segment formed by residues 110 to 114.

Low-temperature 1H-NMR evidence of the folding of isolated ribonuclease S-peptide

The temperature (-7 degrees C to 45 degrees C, pH 5.4) and pH (0 degrees C) dependence of 1H chemical shifts of ribonuclease S-peptide (5 mM, 1 M NaCl) has been measured at 360 MHz. The observed variations evidence the formation of a partial helical structure, involving the fragment Thr-3-Met-13. Two salt-bridges stabilize the helix: those formed by Glu-9- ...His-12+ and Glu-2- ...Arg-10+. The structural features deduced from the 1H-NMR at low temperature for the isolated S-peptide are compatible with the structure shown by the same molecule in the ribonuclease S crystal.

Three-dimensional structure of acidic fibroblast growth factor in solution: effects of binding to a heparin functional analog

Acidic and basic fibroblast growth factors (aFGF and bFGF; FGFs) are paradigms of a group of nine closely related proteins known as the fibroblast growth factor family. FGFs induce mitosis in most mesoderm- and neuroectoderm-derived cells, and appear to be involved in diseases caused by anomalous cell proliferation. In vitro assays show that binding to heparin-like glycosaminoglycans is required to elicit the mitogenic activity of these proteins. It has been shown that myo-inositol hexasulfate (MIHS) emulates heparin in the mitogenesis assays of aFGF, and a low-resolution three-dimensional structure in solution of this protein bound to MIHS has been reported. Here we describe the 1H-NMR three-dimensional structure in solution of the free aFGF. Comparison of this structure with that of the protein bound to MIHS, upgraded to a level of refinement equivalent to that of the free protein, shows that MIHS binding causes some slight conformational changes with an increase in the definition of the structure. In addition, amide exchange H/2H rates of the most protected protons, and exchange data of the intermediate and fast-exchanging ones show that the free protein is less stable (< or = 2 kcal/mol) and more flexible in terms of local unfolding equilibria, respectively, than the MIHS-bound one. Thus, MIHS binding to aFGF causes a decrease of its flexibility, which translates into an enhancement of the definition of its three-dimensional structure. The increase of aFGF rigidity affects regions that include those involved in recognizing the cell membrane receptor. Thus, our data suggest that enhancement of structural definition may play a key role in the modulation of the affinity of aFGF by its receptor, and, consequently, of its specific mitogenic activity.

On the fundamental role of the Glu 2- ... Arg 10+ salt bridge in the folding of isolated ribonuclease A S-peptide

The fundamental role of the Glu 2- ... Arg 10+ salt bridge in the folding of isolated S-peptide (1-19 N-terminal fragment of Ribonuclease A) is demonstrated from the comparison of the helix contents, at 0 degrees C, of S-peptide and related peptides. Helix contents have been determined from the analysis of proton chemical shift vs. temperature curves. The observed data can be accounted for by assuming that two side-chain interactions contribute to stabilize the 3-13 helix of S-peptide, the salt bridges Glu 2- ... Arg 10+ and Glu 9-... His 12+, the former being more effective. The salt bridge Glu 9- ... Arg 10+ turns to a weaker interaction, a hydrogen bond Glu 2 (C delta = 0) ... Arg 10+, on protonation or esterification of the Glu 2 carboxylate.

CSF beta-amyloid, cognition, and APOE genotype in Alzheimer's disease

OBJECTIVES

We examined the relationship between CSF amyloid beta peptide (A beta) concentration and AD severity in 31 probable AD patients and explored whether APOE genotype modifies this relationship.

BACKGROUND

A beta deposition in AD brains has been correlated with disease severity and with APOE-epsilon4 allele frequency. Few studies have examined the effects of APOE genotype on the relationship between CSF A beta and disease severity in an antemortem sample.

METHODS

Patients carried the clinical diagnosis of probable AD and did not have serious medical illness, current or past diagnosis of mood disorder, schizophrenia or alcoholism, or current psychotic features. The Mini-Mental State Examination (MMSE) was administered to the patient within 3 months of CSF collection. CSF was analyzed for A beta1-40 and A beta1-42 by sandwich ELISAs, and APOE genotype was determined by PCR run from blood. Correlations were performed between MMSE score and A beta1-40 and A beta1-42 concentrations while controlling for potential confounding variables.

RESULTS

CSF measures of A beta1-40 and A beta1-42 concentrations were correlated with each other (r = 0.56, df = 28, p < 0.01). CSF A beta1-40 and A beta1-42 concentrations were positively correlated with MMSE score. The negative association between CSF A beta measures and disease severity remained significant after controlling for age (A beta1-40 and MMSE score: r = 0.46, df = 28, p = 0.01; A beta1-42 and MMSE score: r = 0.35, df = 28, p = 0.05). Among the APOE-epsilon3/3 homozygotes there was a significant positive correlation only between A beta1-42 and MMSE score (A beta1-42, r = 0.94, p = 0.02; A beta1-40, r = 0.79, p = 0.11).

CONCLUSIONS

We hypothesize that an increased deposition of A beta in plaques results in decreased CSF A beta concentration. The stronger relationship between MMSE score and CSF A beta, specifically in APOE-epsilon3/3 homozygotes, suggests that patients with APOE-epsilon3/3 genotype may have different pathogenic mechanisms than the other genotypes for A beta deposition or clearance.

Solution structure of acidic fibroblast growth factor bound to 1,3, 6-naphthalenetrisulfonate: a minimal model for the anti-tumoral action of suramins and suradistas

Recent data show that anti-angiogenesis may provide a promising route to treat cancer. Fibroblast growth factors (FGFs) are powerful angiogenic polypeptides, whose mitogenic activity requires the presence of heparin-like compounds. It has been shown that angiogenesis promoted by FGFs on inhibition by monoclonal antibodies and antisense targeting can also inhibit tumour growth. Derivatives of suramin, a polysulfonated binaphthyl urea and binaphthylsulfonated derivatives of distamycin, suradistas, constitute an important group of potential anti-cancer agents. These compounds compete with heparin in forming tight complexes with FGFs. This inhibits the recognition of these growth factors by their tyrosine kinase membrane receptors thereby suppressing their angiogenic activity. Here we show that 1,3,6-naphthalenetrisulfonate, a common chemical function of the suramins and suradistas with the highest anti-angiogenic activity inhibits the mitogenic activity of acidic fibroblast growth factor, and that this inhibition is relieved by increasing concentrations of heparin in the assay. We have also solved the three-dimensional structure in solution of the protein complexed to this compound. The structural data provide clues that may help in understanding the inhibitory effect of suramins and suradistas, and could contribute to the development of new anti-tumoral drugs.

Three-dimensional structure of omega-conotoxin GVIA determined by 1H NMR

omega-Conotoxin GVIA, a peptide of 27 amino acid residues and three disulfide bridges, has been studied by NMR techniques. The complete assignment of the corresponding proton NMR spectra was performed by two-dimensional sequence specific methods at 288 K and pH 3.5. On the basis of 169 distance restraints derived from this analysis, the three-dimensional structure was obtained. A total of 30 initial structures were generated by distance geometry methods and further refined by restrained energy minimization techniques yielding a final set of 8 structures. The mean root-mean-square deviation between each of the 8 structures and the mean atomic coordinates for all residues is 0.82 +/- 0.06 A for the backbone atoms and 1.45 +/- 0.18 A for all non-H atoms. The structure shows a globular folding pattern that is stabilized by the three disulfide linkages and a number of intramolecular hydrogen bonds. A total of 14 hydroxyl groups are found at the periphery fully exposed to the solvent. These groups, together with the charged side chains of Lys and Arg residues emerging radially from the peptide core, provide specific recognition elements for the interaction of this toxin with neuronal calcium channels.

1H-NMR assignment and solution structure of human acidic fibroblast growth factor activated by inositol hexasulfate

A major fragment of human acidic fibroblast growth factor of 132 amino acid residues is shown to be as active and stable as the 139 residue molecule initially described, and commonly used in physiological studies. It is shown that inositol hexasulfate is a good substitute for heparin in both activating and protecting acidic fibroblast growth factor. The complex between the shortened form of the protein and inositol hexasulfate was used to determine the structure of activated acidic fibroblast growth factor in solution. The 1H-NMR spectrum of the complex was totally assigned, and a low-resolution, three-dimensional structure of the protein computed. The global fold of the activated acidic fibroblast growth factor is similar to that proposed for a crystallized variant of the protein obtained by genetic engineering whose activity is not dependent on heparin. The inositol hexasulfate binds to the protein through the positively charged groups of Lys126, Lys127, Arg133 and Lys142 side-chains. The computed three-dimensional structure suggests that inositol hexasulfate may stabilize and activate the protein by conferring rigidity to the hairpin involving beta-strands 10 and 11.

Periodic properties of proton conformational shifts in isolated protein helices. An experimental study

In this work, the helix-forming residues in fragments of several proteins (ribonuclease, thermolysin, tendamistat and angiogenin) were identified by NOE and the helix proton shifts were measured as delta changes associated with helix-population increments driven by trifluoroethanol addition. When estimated in this way, a regular pattern of helix conformational shifts was clearly seen in the delta delta versus sequence profiles of all the peptides studied. The helix periodicity of the H alpha and H beta resonances was especially clear, an observation that earlier statistical studies of protein delta values failed to predict. Amide protons showed the largest helix shifts, but with a less-sharply defined periodic character. Aromatic residues considerably distorted the periodicity of the helix amide shifts in some peptides, as evidenced by the delta shifts of a RNase A fragment 1-15 analog in which the two aromatic residues were replaced by Ala. The relationship between helix periodicity and peptide amphiphatic character is discussed.