NMR solution structure of the 205-316 C-terminal fragment of thermolysin. An example of dimerization coupled to partial unfolding

The solution structure of the C-terminal fragment 205-316 of thermolysin has been determined by 1H-NMR methods. The fragment forms a dimer in which each subunit has two different regions: the largely disordered N-terminal segment 205-260 and the structurally well-defined segment 261-316. The structured part of each subunit is composed of three helices and is largely coincident with the corresponding region in the solution structure of the dimer formed by the shorter fragment 255-316, which in turn coincides with the crystallographic structure of intact thermolysin. As with the fragment 255-316, the subunit interface is highly hydrophobic and coincides topologically with the one between the segment 255-316 and the rest of the protein in the intact enzyme. A fourth helix (residues 235-246), present in the segment 205-316 of native thermolysin, is mostly disordered in the dimer formed by the fragment 205-316. The location of the fourth helix in the native structure of intact thermolysin does not allow the formation of the dimer interface observed in the solution structure of the fragment 255-316. Under the NMR conditions, dimer formation is energetically more favorable than the dissociated monomers. The latter, based on calorimetric data, was proposed to have partial structure in the region 205-254 as in native thermolysin. Thus, it appears that the assembly of the dimer would require an initial unfolding in the region 205-254 of the monomer.

Three-dimensional solution structure and stability of phage 434 Cro protein

1H NMR resonances of the phage 434 Cro protein were assigned using standard 2D NMR methods, and its solution structure determined using 867 distance constraints in distance geometry (DIANA) calculations ultimately refined by restrained molecular dynamics (GROMOS). In the 20 best NMR structures, the average pairwise backbone and heavy atom RMSDs are 0.63 +/- 0.14 and 1.53 +/- 0.15 A, respectively, for the structurally well-defined residues 4-65. Residues 1-3 and 66-71 at the N- and C-termini are structurally disordered. The region 4-65 includes five alpha-helices and tight turns which define the hydrophobic core of the protein. The backbone and heavy atom RMSDs for residues 4-65 are 0.92 +/- 0.12 and 1.99 +/- 0.12 A, respectively, for the NMR versus the crystal structures, but there are significant differences in the side-chain conformations and solvent accessibilities for some core residues. Analytical ultracentrifugation experiments confirm that 434 Cro is monomeric even at the high NMR concentrations. 434 Cro folding under NMR solution conditions is two-state as indicated by coincident urea denaturation curves from circular dichroism and intrinsic fluorescence measurements. They yield values for 434 Cro stability which show good correspondence to the free energy for global unfolding determined by NMR hydrogen exchange measurements for the slowest exchanging amide protons.

Non-native local interactions in protein folding and stability: introducing a helical tendency in the all beta-sheet alpha-spectrin SH3 domain

The relative importance of secondary structure interactions versus tertiary interactions for stabilising and guiding the folding process is a matter for discussion. Phenomenological models of protein folding assign an important role to local contacts in protein folding and stability. On the other hand, simplistic lattice simulations find that secondary structure is mainly the product of protein compaction and that optimisation of folding speed seems to require small contributions of local contacts to the stability of the folded state. To examine the extent to which secondary structure propensities influence protein folding and stability, we have designed mutations that introduce a strong non-native helical propensity in the first 19 residues of the alpha-spectrin SH3 domain. The mutant proteins have the same three-dimensional structure as the wild-type, but they are less stable and have less co-operative folding transitions. There seems to be a relationship between the non-native helical propensity and the compaction of the denatured state. This suggests that in the denatured ensemble under native conditions there is a significant proportion of compact structures with non-native secondary structures. Our results demonstrate that non-local interactions can overcome strong non-native secondary structure propensities and, more important, that optimisation of folding speed and co-operativity requires the latter to be relatively small.

Absence of detectable PML-RAR alpha fusion transcripts in long-term remission patients after BMT for acute promyelocytic leukemia

Twenty patients with APL in long-term remission after BMT were analyzed for the presence of the PML-RAR alpha fusion gene by RT-PCR. Ten patients had undergone autologous BMT (six of them peripheral blood stem cell transplantation) and 10 allogeneic BMT. A total of 60 samples were examined by two different protocols. Of the eight patients studied just before conditioning, five showed PML-RAR alpha transcript prior to transplantation. Three of them were in CR and became PCR negative early post-transplantation. The other two patients, that were not in CR before transplant, remained PCR positive, relapsed early post-transplant and died. In the remaining patients no PML-RAR alpha transcripts were visible throughout their post-BMT courses. Our data show that long-term remission after BMT in APL patients is associated with eradication of cells carrying the PML-RAR alpha transcript, and that continued positivity of this test predicts subsequent relapse. The fact of the disappearance of PML-RAR alpha transcript early after BMT in patients previously positive suggest that transplant is capable of curing APL mainly through antileukemic action of the conditioning regimen and therefore, transplantation must be indicated in CR patients if a positive RT-PCR remains after treatment with ATRA plus chemotherapy.

[The treatment of the tracheobronchomalacia in pediatric age]

OBJECTIVE

Aortopexy is the more extended treatment for severe tracheomalacia, when it fails, reintervention and other procedures are necessary. We present our experience in the treatment of this pathology.

MATERIAL AND METHODS

Tracheomalacia, bronchomalacia and tracheobroncomalacia cases during a twelve year period (1983-1995) were reviewed (type, age, symptoms, surgical procedures and results were collected).

RESULTS

Nineteen patients (9 males, 10 females) presented tracheobronchomalacia in our Hospital. Diagnosis was made by bronchoscopy in all of them: nine cases of tracheomalacia, five bronchomalacias and five suprastomal malacias were found. Mean diagnosis age was twenty four months (newborn-twelve years). Ten patients were managed nonoperatively, five with anterior cricoideal suspension and two cases were treated by aortopexy; one of them, after 2 months of respiratory stridor and recurrent respiratory arrest, needed an endoscopically placed intraluminal expandable Palmaz Prothesis. This prothesis was removed two years later. In this moment, the patient is doing well without stridor or respiratory symptoms.

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.

[Our experience in neonatal surgery in a 15-year period. Follow-up of 1,003 cases]

From 1982 to 1994, 1.003 cases of surgical newborns have been retrospectively studied. Frequency and epidemiology have been evaluated, so as associated malformations. Prenatal diagnosis was made in 72 cases (7.1%). The most frequent entity was intestinal atresia, with 122 cases (12.1%), followed by necrotizing enterocolitis in 80 cases (7.9%), nevertheless this last one was the most frequent finding in preterm newborns. Esophageal atresia was found in 57 cases (5.6%). Association with other malformations was found in 127 cases (12.6%), and 32 cases of them (3.1%) constituted congenital malformations syndromes. The number of surgical newborns has increased in the last years, mainly due to ambulatory surgery. Global mortality of operated patients was 62 cases (5.9%); the highest mortality index was for congenital diaphragmatic hernia (33.5%), followed by necrotizing enterocolitis (28%). Mortality rate has decreased in recent years, due to improving in management and treatment of these patients, and the consolidation of surgical newborn units. Future efforts should be aimed for decreasing in mortality and improving the standard of life of these patients.

Conformational analysis of peptides corresponding to beta-hairpins and a beta-sheet that represent the entire sequence of the alpha-spectrin SH3 domain

In an attempt to identify potential folding initiation sites for a small, all beta-protein domain, we have examined the conformational preferences in aqueous solution of peptides that span the entire length of the alpha-spectrin SH3 domain, using proton nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy. Two of the peptides correspond to beta-hairpins (m6 and m8), one to the RT-loop (m4, which can be considered as a distorted beta-hairpin), one to a beta-hairpin created by joining the N and C-terminal strands via a small linker (m2) and the fifth one to a three-stranded antiparallel beta-sheet composed of beta-hairpins m6 and m8 (m68). To estimate the distorting effect of the aromatic side-chains of Trp41 and Trp42 on the CD and NMR spectra of peptides m6, m8 and m68, we have also analyzed a short, ten-residue random-coil peptide containing residues 39 to 44 (mC). The CD and NMR results indicate that none of the peptides populates to a large extent a particular secondary structure conformation. However, careful anlaysis of the NMR data reveals that peptides m6, m8 and m68 could adopt, to a small extent, native-like conformations, although in the case of peptide m68 there is also evidence of the presence of non-native helical conformations. Addition of 30% (v/v) 2,2,2-trifluoroethanol stabilizes the appearance of non-native helical populations in some small regions of peptides m2, m4, m8 and m68, while it induces a native-like conformation in peptide m6. Those fragments corresponding to the two real beta-hairpins in the protein are the ones which exhibit some tendency to populate native-like structures (m6 and m8), while the ones corresponding to the long RT-loop (m4) or the newly created one (m2) are mainly unstructured in water solution. Although there could be some local interactions that favor the acquisition of a native secondary structure in this domain, tertiary interactions should play a major role in defining its native secondary structure.

Conformational investigation of designed short linear peptides able to fold into beta-hairpin structures in aqueous solution

BACKGROUND

Formation of secondary structure plays an important role in the early stages of protein folding. The conformational analysis of designed peptides has proved to be very useful for identifying the interactions responsible for the formation and stability of alpha-helices. However, very little is known about the factors leading to the formation of beta-hairpins. In order to get a good beta-hairpin-forming model peptide, two peptides were designed on the basis of beta-sheet propensities and individual statistical probabilities in the turn sites, together with solubility criteria. The conformational properties of the two peptides were analyzed by two-dimensional NMR methods.

RESULTS

Long-range cross-correlations observed in NOE and ROE spectra, together with other NMR evidence, show that peptide IYSNPDGTWT forms a highly populated beta-hairpin in aqueous solution with a type I beta-turn plus a G1 beta-bulge conformation in the chain-bend region. The analogous peptide with a Pro5 substituted by Ser forms, in addition to the previous conformation, a second beta-hairpin with a standard type I beta-turn conformation, and the two forms are in fast dynamic equilibrium with one another. The effect of pH demonstrates the existence of a stabilizing interaction between the Asn and Asp sidechains. The populations of beta-hairpin conformations increase in the presence of trifluoroethanol (a structure-enhancing solvent). On the other hand, some residual structure persists at a high denaturant concentration (8 M urea).

CONCLUSIONS

This work highlights the importance of the beta-turn residue composition in determining the particular type of beta-hairpin adopted by a peptide, though a role of interstrand sidechain interactions in the stabilization of the formed beta-hairpin is not discarded. The fact that trifluoroethanol can stabilize alpha-helices or beta-hairpins depending on the intrinsic properties of the peptide sequence is again shown. An additional example of the presence of residual structure under denaturing conditions is also presented.

Interactions responsible for the pH dependence of the beta-hairpin conformational population formed by a designed linear peptide

In a previous work [Blanco, F.J., Jiménez, M.A., Herranz, J., Rico, M., Santoro, J. & Nieto, J. L. (1993) J. Am. Chem. Soc. 115, 5887-5888] we showed that a short, designed linear peptide, YQNPDGSQA (peptide 1), can form a monomeric beta hairpin in aqueous solution. The pH dependence of the beta-hairpin conformation formed by the designed peptide and a series of related peptides has been examined in this work using 1H-NMR methods. Three pH-dependent interactions have been identified: a local interaction, unimportant structurally, between the C-terminal carboxylate group and the side-chain amide group of Q8; an electrostatic interaction between the main-chain N-terminus and C-terminus; and a hydrogen bond involving the side-chain amide protons of N3 and the side-chain carboxylate group of D5. The latter two interactions are particularly relevant as they increase the population of the beta-hairpin conformation. We also observe in the mutant peptide A9H that the interaction between Y1 and H9 (of the type proposed to exist in proteins) does not contribute to beta-hairpin stabilisation in our peptide system. Peptide 1 is, therefore, a very suitable model to examine the different interactions that contribute to beta-hairpin stability.

Solvent polarity-dependent structural refolding: a CD and NMR study of a 15 residue peptide

A close association between the HIV surface protein gp120 and the CD4 T cell receptor initiates the viral multiplication cycle. A 15 amino acid peptide (LAV) within the CD4 binding domain of gp 120 has been shown to retain receptor binding ability. The structural behavior of the LAV peptide has been studied by CD and NMR methods in aqueous solution and upon addition of trifluoroethanol (TFE) to emulate the relatively apolar conditions at the membrane bound receptor. Previous work has shown that the LAV peptide folds into a beta-pleated structure in more polar buffer/TFE mixtures, while a concerted structural change can be observed at a concentration of 60% TFE (v/v). This abrupt, cooperative refolding from a regular beta-sheet to a helical secondary structure is known as "switch" behavior. Former CD experiments with LAV sequence variants have supported the assumption that four amino acids at the N-terminus (LPCR) are indispensable for the "switch." The tetrad has a strong beta-turn forming potential. The suggestion has been formulated that the tetrad can act as a nucleation site governing the refolding. The present NMR study of the LAV peptide in TFE gives evidence for a 3(10)-helix suggesting that the tetrad adopts a type III beta-turn and promotes the formation of a similar bend in the next overlapping tetrad until the sequence is restructured into a 3(10)-helix at a critical polarity favoring intrachain hydrogen bonds.

[Retrospective analysis of 80 cases of neonatal necrotizing enterocolitis]

We present the cases of necrotizing enterocolitis (NEC) treated in our hospital between 1980 and 1994, in order to analyze the risk factors that appear in the disease. We elaborate treatment and follow-up protocols. Prematurity, low birth weight and perinatal stress have a significant influence in NEC. Hemodinamic inestability, bloody stools, abdominal distension with decrease gastric outlet, along with significant radiological evidence in 90 percent of the cases, should rise suspition of NEC. We find fundamental the prevention of the disease in premature newborns with risk factors. Mean gestational age was 33 weeks. Prematurity was found in 87.5 percent of the patients, with a mean birth weight of 1683 g. Symptoms appeared at the age of 14 days. 32 percent of the cases were operated, 13 cases (16%) presenting with pneumoperitoneum, and a Mortality rate 15 percent. We treated 15 patients with colonic stenosis by resection and end-to-end anastomosis, with 6 percent mortality global mortality rate for NEC has been 28 percent.

[Rectocolonic plasty using mechanical stapler as a surgical solution in complications of megacolon]

Hirschsprung's disease surgically treated with Duhamel's technique in which no mechanical suture has been used, usually presents, as main complication, cronic constipation, due to fecalomas in the rectal pouch. In our experience (30 cases plus four patients sent to our hospital for reintervention), this complication is not present when mechanical suture is introduced to the Duhamel's Technique. This allows us to assure that perineal rectocoloplasty, with auto-suture material is a precise optional treatment, with excellent results and allows the chance of not going through laparotomy in those cases that require reintervention.

Acylated flavonol sophorotriosides from pea shoots

Seven flavonols were isolated and identified from Pisum sativum (cv Solara) shoots. The 3-glucoside, and 3-sophorotrioside [beta-D-glucopyranosyl(1-->2)-beta-D- glucopyranosyl(1-->2)-beta-D-glucopyranoside] of quercetin, the 3-sophorotrioside of kaempferol, and the acylated derivatives of quercetin 3-sophorotrioside with p-coumaric, caffeic, ferulic and sinapic acids on the hydroxyl at the 6-position of the terminal sugar. The caffeic and sinapic acid esters are two new naturally occurring compounds. This is the first report in which the structures of the p-coumaryl- and ferulyl-sophorotriosides of quercetin, which were previously reported from pea leaves, have been completely established by means of 1H NMR studies including COSY, NOESY and TOCSY experiments.

A tyrosine-containing motif mediates ER retention of CD3-epsilon and adopts a helix-turn structure

The CD3-epsilon endoplasmic reticulum (ER) retention motif has been characterized by mutagenesis and NMR spectroscopy. Tyr177, Leu180 and Arg183 are involved in ER retention. The motif forms an elongated alpha-helix in which the tyrosine and leucine residues are closely apposed, followed by a beta I' turn that places Arg183 in the vicinity of Leu180. The structure formed by Tyr177 and the leucine in position +3 is reminiscent of the beta-turn structure adopted by tyrosine-containing endocytosis signals. Moreover, substitution of the transferrin receptor (TfR) internalization sequence by the CD3-epsilon motif still allowed the rapid internalization of the TfR and, conversely, the chimeric protein resulting from the substitution of the CD3-epsilon motif by the endocytosis signal of the low density lipoprotein receptor was ER located. These data support the idea of a functional homology between the two types of signal.

Structural analysis of peptides encompassing all alpha-helices of three alpha/beta parallel proteins: Che-Y, flavodoxin and P21-ras: implications for alpha-helix stability and the folding of alpha/beta parallel proteins

In an attempt to delineate the early folding events of structurally related proteins with no sequence homology, peptides including all five alpha-helices of three alpha/beta parallel open-sheet proteins, Che-Y, flavodoxin and P21-ras, have been analyzed by circular dichroism (far-UV CD) and nuclear magnetic resonance (NMR) in water and 30% (v/v) trifluoroethanol (TFE). Comparison between the helical content estimations from far-UV CD and the results from the NMR analysis renders a reasonably good qualitative correlation, indicating that the same phenomenon is underlined by both methods. Helix limits, as indicated by the existence of (i,i + 3) nuclear Overhauser effect (NOE) cross-correlations and significant up-field conformational shifts of the C alpha H protons, are practically coincident with those in the folded protein. On the other hand, the conformation of the side-chains differs markedly from those in the folded protein. Observation of NOE cross-correlations between pairs of residues at positions i,i + 3 has been used to statistically quantify free energies of i,i + 3 side-chain-side-chain interactions between the different pairs of residues in an alpha-helix. This analysis indicates that interactions between hydrophobic side-chains seem to be quite favorable for helix formation. The behaviour in aqueous solution of the structural equivalent peptides for the three proteins is quite unrelated except for the peptides corresponding to helices two and five. We postulate that, in the alpha/beta parallel proteins, those helices that join two beta-strands flanking another non-consecutive beta-strand should not be stable for folding reasons.

[Treatment of post-traumatic pancreatic pseudocyst by percutaneous Huisman's drainage]

Pancreatic pseudocysts is a complication of acute posttraumatic pancreatitis. They usually cause recurrent abdominal pain, nausea, vomiting and elevation of serum amylase levels. A history of epigastric blunt trauma, the before mentioned clinical signs and echographic or scanning studies may lead to a certain diagnosis. Although most of them resolve spontaneously, some persist and active therapeutic measures are required. Surgical internal drainage has been the operative technique of choice in children. Nevertheless, treatment can be achieved by percutaneous aspiration or drainage of pancreatic recurrent collections. We present our experience in two children with posttraumatic pancreatic pseudocyst, treated successfully by means of a percutaneous transabdominal pig-tail catheter (Huisman catheter). The technique of catheter placement and clinical aspects are discussed.

NMR solution structure of the C-terminal fragment 255-316 of thermolysin: a dimer formed by subunits having the native structure

The solution structure of the C-terminal fragment 255-316 of thermolysin has been determined by two-dimensional proton NMR methods. For this disulfide-free fragment there was a previous proposal according to which it would fold into a stable helical structure forming a dimer at concentrations above 0.06 mM. A complete assignment of the proton NMR resonances of the backbone and amino acid side chains of the fragment was first performed using standard sequential assignment methods. On the basis of 729 distance constraints derived from unambiguously assigned nuclear Overhauser effect (NOE) proton connectivities, the three-dimensional structure of a monomeric unit was then determined by using distance geometry and restrained molecular dynamic methods. The globular structure of fragment 255-316 of thermolysin in solution, composed of three helices, is largely coincident with that of the corresponding region in the crystallographic structure of intact thermolysin [Holmes, M. A., & Matthews, B. W. (1982) J. Mol. Biol. 160, 623-639]. This fact allowed identification as intersubunit of up to 52 NOE cross correlations, which were used to dock the two subunits into a symmetric dimer structure. The obtained dimeric structure served as the starting structure in a final restrained molecular dynamic calculation subjected to a total of 1562 distance constraints. In the resulting dimeric structure, the interface between the two subunits, of a marked hydrophobic character, coincides topologically with the one between the 255-316 fragment and the rest of the protein in the intact enzyme. The present work decisively shows that the thermolysin fragment 255-316 can attain a stable and nativelike structure independently of the rest of the polypeptide chain. Considering that the thermolysin molecule is constituted of two structural domains of equal size (residues 1-157 and 158-316), the results of this study show that autonomously folding units can be substantially smaller than entire domains.

Helix stop and start signals in peptides and proteins. The capping box does not necessarily prevent helix elongation

Recently, several papers have addressed the existence of helix stop signals at the beginning of alpha-helices. It has been indicated that the existence of a reciprocal backbone-side-chain hydrogen-bond interaction, designated the capping box, could be one of these signals. The fingerprint sequence of this capping box is Ser/Thr-X-X-Glu/Gln. In the fifth alpha-helix of the chemotactic alpha/beta parallel protein CheY there is such a sequence in the middle of the helix. In a peptide corresponding to this alpha-helix the capping box is bypassed, as deduced from NMR analysis. However, making the peptide shorter so that the capping box fingerprint is closer to the beginning of the peptide results in the formation of the capping box. These results indicate that, although the capping box could play a role in stabilizing and nucleating helical peptides in solution, it is not necessarily a stop signal and can be bypassed when favourable interactions exist between the surrounding residues.

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.

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.

Helix formation by the phospholipase A2 38-59 fragment: influence of chain shortening and dimerization monitored by nmr chemical shifts

The solution structure of a peptide fragment corresponding to the 38-59 region of porcine phospholipase A2 has been investigated using CD, nmr chemical shifts, and nuclear overhauser effects (NOEs). This isolated fragment of phospholipase forms an alpha-helix spanning residues 38-55, very similar to the one found in the native protein, except for residues 56-58, which were helical in the crystal but found random in solution. Addition of triflouroethanol (TFE) merely increased helix population but it did not redefine helix limits. To investigate how the folding information, in particular that concerning eventual helix start and stop signals, was coded in this particular amino acid sequence, the helices formed by synthetic peptides reproducing sections of this phospholipase 38-59 fragment, namely 40-59, 42-59, 38-50, and 45-57, were characterized using NOEs and helix populations quantitatively evaluated on different peptide chain segments using nmr chemical shifts in two solvents (H2O and 30% TFE/H2O). A set of nmr spectra was also recorded and assigned under denaturing conditions (6M urea) to obtain reliable values for the chemical shifts of each peptide in the random state. Based on chemical shift data, it was concluded that the helix formed by the phospholipase 38-59 fragment was not abruptly, but progressively, destabilized all along its length by successive elimination of residues at the N end, while the removal of residues at the C end affected helix stability more locally and to a lesser extent. These results are consistent with the idea that there are not single residues responsible for helix initiation or helix stability, and they also evidence an asymmetry for contributions to helix stability by residues located at the two chain ends. The restriction of molecular mobility caused by linking with a disulphide bridge at Cys 51 two identical 38-59 peptide chains did not increase helix stability. The helix formed by the covalently formed homodimer was very similar in length and population to that formed by the monomer.

[Orthotopic heart transplant. Study of early morbimortality (< or = 30 days). Experience at the Reina Sofía Hospital (Córdoba)]

From may 1986 to december 1991, we have performed 90 heart transplantation in the Hospital "Reina Sofía" from Córdoba. In the present study we analyze the early morbidity and mortality in a retrospective study on complications and factors determining its incidence. Seventy patients were male (86%) and 13 female (14%). Age ranged from 12 and 65 years. The 31% of patients needed in pharmacological support before transplantation, 15 of them were operated in a emergency situation because of cardiogenic shock. The pulmonary resistances oscillated between 0.5 and 8.7 units/m2 (Wood) (mean 2.5 +/- 1.4 units/m2). The mean time of ischaemia was 136 +/- 38 minutes (range 5-255 min). Hospital mortality (< or = 30 days) was 8.8% (8/90). No predictive factors from donor and recipient were found. Three main influences on complications were analyzed: a) influence of myocardial temperature, b) role of hematic cardioplegia, and c) usefulness of Aprotinin. Eighteen patients (20%) developed severe bradyarrhythmia needing a pacemaker in the post-operative period. We found a significant relationship with myocardial temperature (4.3 +/- 2.1 vs 6.2 +/- 2.6; p < 0.05) and transport solution temperature (5.8 +/- 2.3 vs 7.3 +/- 1.9; p < 0.05). No significant influence was found on the time of ischaemia, previous heart disease, previous treatment with Amiodarona, clinical condition, etc.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.