Antithrombotic activity of AT-1015, a potent 5-HT(2A) receptor antagonist, in rat arterial thrombosis model and its effect on bleeding time

The antithrombotic activity of N-[2-(4-(5H-dibenzo[a,d]cyclohepten-5-ylidene)piperidino)ethyl]-1-formyl-4-piperidinecarboxamide monohydrochloride monohydrate (AT-1015; a 5-HT(2A) receptor antagonist) was studied in a photochemically induced arterial thrombosis (PIT) model in the rat femoral artery, and in the tail transection bleeding time test. Ticlopidine (an antiplatelet agent) and sarpogrelate (a selective 5-HT(2A) receptor antagonist) were studied as reference compounds. Pretreatment with AT-1015 (1 mg/kg, p.o.) significantly prolonged the time required to occlusion of the artery with thrombus, and the effect (3 mg/kg, p.o.) persisted for 24 h with significant inhibition of 5-HT-induced vascular contraction. Ticlopidine and sarpogrelate also significantly prolonged the time to occlusion at 100 mg/kg, p.o. Sarpogrelate (300 mg/kg, p.o.) showed the similar antithrombotic efficacy to AT-1015 (3 mg/kg, p.o.), while the effect disappeared within 6 h. No significant bleeding time prolongation was observed at 10 mg/kg of AT-1015, which is 10 times higher than the antithrombotic effective dose; whereas ticlopidine significantly prolonged bleeding time at the same dose as the antithrombotic effective dose. These results suggested that AT-1015 is a potent and long-acting oral antithrombotic agent in this model, which may be elucidated by its potent and long-acting inhibition of vasoconstriction through 5-HT(2A) receptor.

Refolding of beta-lactoglobulin studied by stopped-flow circular dichroism at subzero temperatures

Refolding of bovine beta-lactoglobulin was studied by stopped-flow circular dichroism at subzero temperatures. In ethylene glycol 45%-buffer 55% at -15 degrees C, the isomerization rate from the kinetic intermediate rich in alpha-helix to the native state is approximately 300-fold slower than that at 4 degrees C in the absence of ethylene glycol, whereas the initial folding is completed within the dead time of the stopped-flow apparatus (10 ms). At -28 degrees C, we observed at least three phases; the fastest process, accompanied by an increase of alpha-helix content, is completed within the dead time of the stopped-flow apparatus (10 ms), the second phase, accompanied by an increase of alpha-helix content with the rate of 2 s(-1), and the third phase, accompanied by a decrease of alpha-helix content. This last phase, corresponding to the isomerization process at -15 degrees C described above, was so slow that we could not monitor any changes within 4 h. Based on the findings above, we propose that rapid alpha-helix formation and their concurrent collapse are common even in proteins rich in beta-structure in their native forms.

Clinical implications of duplicated mtDNA in Pearson syndrome

We report on a seven-year-old Japanese boy with Pearson syndrome, which is characterized by refractory sideroblastic anemia with vacuolization of marrow precursors and dysfunction of the exocrine pancreas, and caused by mitochondrial (mt) DNA deletions and duplications. Although analysis with Southern hybridization on his bone marrow cells at age one year or on the muscle at age five years did not detect any duplications of mtDNA, an analysis after death at age seven years detected them in the kidney, heart, and even in the bone marrow. Using long PCR to specifically amplify duplicated mtDNA, we found duplications in all biopsy and postmortem samples, indicating that duplications had been present in the patient since his early life, and that the number of duplications increased with age. The results indicate some dynamism in the mtDNA duplication and that the dynamism may imply clinical importance.

Inhibitory effects of a newly synthesized 5-HT2 receptor antagonist, AT-1015 (N-[2-[4-(5H-dibenzo[a,d]cyclohepten-5-ylidene)piperidino]-ethyl]-1-for myl-4-piperidinecarboxamide monohydrochloride monohydrate), on contraction and relaxation of pig coronary arteries induced by 5-HT and alpha-methylserotonin: comparison with ketanserin

Inhibitory effects of a newly synthesized 5-HT2 receptor antagonist, AT-1015 (N-[2-[4-(5H-dibenzo[a,d]cyclohepten-5-ylidene)piperidinolethyl ]-1-formyl-4-piperidinecarboxamide monohydrochloride monohydrate) on contraction and relaxation of coronary arteries of pig hearts mediated by 5-HT2 subtypes were evaluated and these results were compared with those of ketanserin. Contraction and relaxation were determined by adding 5-HT or alpha-methylserotonin (alpha-Me-5-HT) as agonists. Although ketanserin induced rightward shifts of contraction, AT-1015 inhibited the maximal response. In addition, ketanserin inhibited relaxation induced by high concentration of agonists, but there were no inhibitory effects of AT-1015 on relaxation. Thus, these results suggest that AT-1015 is a strong non-competitive 5-HT2 antagonist in porcine coronary arteries and that this drug clearly exhibited different effects on the contraction and relaxation of coronary arteries of pig hearts from those of ketanserin.

GroES co-chaperonin small-angle X-ray scattering study shows ring orifice increase in solution

GroES consists of seven identical 10 kDa subunits and is involved in assisting protein folding as the partner of another oligomeric protein, the GroEL chaperonin. Here we studied the GroES structure in solution using small-angle X-ray scattering (SAXS). The SAXS pattern, calculated for the GroES crystal structure, was found to be different from the experimental one measured in solution. The synchronic shift in the radial direction and some turning of the protein subunits eliminate the difference and result in the increase of the hole diameter in the GroES ring-like structure from 8 A in the crystal to 21 A in solution.

AT-1015, a novel serotonin (5-HT)2 receptor antagonist, blocks vascular and platelet 5-HT2A receptors and prevents the laurate-induced peripheral vascular lesion in rats

The serotonin (5-HT2A) antagonistic activities and the protective effect on laurate-induced peripheral vascular lesions of AT-1015, a novel 5-HT2 receptor antagonist, were investigated. In platelet aggregation, AT-1015 selectively inhibited in vitro 5-HT2A receptor-mediated aggregation, and the activity was almost equivalent to that of ketanserin (5-HT2A/2C receptor antagonist) and 100 times more potent than sarpogrelate (5-HT2A receptor antagonist). AT-1015 also inhibited 5-HT2A receptor-mediated aggregation by oral administration in rat, and the dose required for inhibition was equivalent to ketanserin. In a 5-HT-induced vasoconstriction study in rat, AT-1015 slightly reduced maximal contraction and caused a rightward shift of the concentration-response curve (pKB value, 9.5), which was unlike competitive inhibitors such as ketanserin and sarpogrelate (pA2 value, 9.3 and 8.7, respectively). Moreover, the ex vivo inhibitory activity significantly remained after oral administration (1 mg/kg). In the rat peripheral vascular lesion model, AT-1015 (1 mg/kg, p.o.) effectively prevented progression of peripheral lesions, and it was more potent compared with ketanserin, sarpogrelate, and cilostazol. These results suggest that AT-1015 is a potent 5-HT2A receptor antagonist, and its insurmountable antagonism may be relevant to its therapeutic potential in peripheral vascular disease.

pH-dependent unfolding of aspergillopepsin II studied by small-angle X-ray scattering

Aspergillopepsin II (EC 3.4.23.6) secreted from the fungus Aspergillus niger var. macrosporus is a non-pepsin-type acid proteinase. It consists of two polypeptide chains (i.e., a heavy chain and a light chain), which are bound noncovalently to each other. The pH titration analysis using small-angle X-ray scattering (SAXS) as well as circular dichroism (CD) and gel filtration indicated that the enzyme was unfolded around a neutral pH with concomitant dissociation of the two chains. Detailed analyses showed that the midpoint pH values for the unfolding are not coincident with one another (pH 6.1 in circular dichroism and gel filtration, pH 6.4 in zero-angle intensity of SAXS, pH 6.8 in radius of gyration). The difference between these values suggested the existence of an intermediate state during the unfolding. Further analyses of the SAXS data showed that the heavy chain just after the dissociation still kept molecular compactness and that it gradually increased its dimensions as the pH was further raised. Noncoincidence of the two phenomena (i.e., chain dissociation and swelling) led to elucidation of a novel intermediate state during unfolding, which was confirmed by the subsequent singular value decomposition (SVD) analysis.

Apparent radii of the native, stable intermediates and unfolded conformers of the alpha-subunit of tryptophan synthase from E. coli, a TIM barrel protein

The urea-induced equilibrium unfolding of the alpha-subunit of tryptophan synthase (alphaTS) from Escherichia coli can be described by a four-state model, N right harpoon over left harpoon I1 right harpoon over left harpoon I2 right harpoon over left harpoon U, involving two highly populated intermediates, I1 and I2 [Gualfetti, P. J., Bilsel, O., and Matthews, C. R. (1999) Protein Sci. 8, 1623-1635]. To extend the physical characterization of these stable forms, the apparent radius was measured by several techniques. Size-exclusion chromatography (SEC), analytical ultracentrifugation (UC), and dynamic light scattering (DLS) experiments yield an apparent Stokes radius, R(s), of approximately 24 A for the native state of alphaTS. The small-angle X-ray scattering (SAXS) experiment yields a radius of gyration, R(g), of 19.1 A, consistent with the value predicted from the X-ray structure and the Stokes radius. As the equilibrium is shifted to favor I1 at approximately 3.2 M and I2 at 5.0 M urea, SEC and UC show that R(s) increases from approximately 38 to approximately 52 A. Measurements of the radius by DLS and SAXS between 2 and 4.5 M urea were complicated by the self-association of the I1 species at the relatively high concentrations required by those techniques. Above 6 M urea, SEC and UC reveal that R(s) increases linearly with increasing urea concentration to approximately 54 A at 8 M urea. The measurements of R(s) by DLS and R(g) by SAXS are sufficiently imprecise that both values appear to be identical for the I2 and U states and, considering the errors, are in good agreement with the results from SEC and UC. Thermodynamic parameters extracted from the SEC data for the N right harpoon over left harpoon I1 and I1 right harpoon over left harpoon I2 transitions agree with those from the optical data, showing that this technique accurately monitors a part of the equilibrium model. The lack of sensitivity to the I2 right harpoon over left harpoon U transition, beyond a simple swelling of both species with increasing urea concentration, implies that the Stokes radii for the I2 and U states are not distinguishable. Surprisingly, the hydrophobic core known to stabilize I2 at 5.0 M urea [Saab-Rincón, G., Gualfetti, P. J., and Matthews, C. R. (1996) Biochemistry 35, 1988-1994] develops without a significant contraction of the polypeptide, i.e., beyond that experienced by the unfolded form at decreasing urea concentrations. Kratky plots of the SAXS data, however, reveal that I2, similar to N and I1, has a globular structure while U has a more random coil-like form. By contrast, the formation of substantial secondary structure and the burial of aromatic side chains in I1 and, eventually, N are accompanied by substantial decreases in their Stokes radii and, presumably, the size of their respective conformational ensembles.

Interhospital network system using the worldwide web and the common gateway interface

We constructed an interhospital network system using the worldwide web (WWW) and the Common Gateway Interface (CGI). Original clinical images are digitized and stored as a database for educational and research purposes. Personal computers (PCs) are available for data treatment and browsing. Our system is simple, as digitized images are stored into a Unix server machine. Images of important and interesting clinical cases are selected and registered into the image database using CGI. The main image format is 8- or 12-bit Joint Photographic Experts Group (JPEG) image. Original clinical images are finally stored in CD-ROM using a CD recorder. The image viewer can browse all of the images for one case at once as thumbnail pictures; image quality can be selected depending on the user's purpose. Using the network system, clinical images of interesting cases can be rapidly transmitted and discussed with other related hospitals. Data transmission from relational hospitals takes 1 to 2 minutes per 500 Kbyte of data. More distant hospitals (e.g., Rakusai Hospital, Kyoto) takes 1 minute more. The mean number of accesses our image database in a recent 3-month period was 470. There is a total about 200 cases in our image database, acquired over the past 2 years. Our system is useful for communication and image treatment between hospitals and we will describe the elements of our system and image database.

Unfolding and refolding of dimeric creatine kinase equilibrium and kinetic studies

Equilibrium and kinetic studies of the guanidine hydrochloride induced unfolding-refolding of dimeric cytoplasmic creatine kinase have been monitored by intrinsic fluorescence, far ultraviolet circular dichroism, and 1-anilinonaphthalene-8-sulfonate binding. The GuHCl induced equilibrium-unfolding curve shows two transitions, indicating the presence of at least one stable equilibrium intermediate in GuHCl solutions of moderate concentrations. This intermediate is an inactive monomer with all of the thiol groups exposed. The thermodynamic parameters obtained by analysis using a three-state model indicate that this intermediate is similar in energy to the fully unfolded state. There is a burst phase in the refolding kinetics due to formation of an intermediate within the dead time of mixing (15 ms) in the stopped-flow apparatus. Further refolding to the native state after the burst phase follows biphasic kinetics. The properties of the burst phase and equilibrium intermediates were studied and compared. The results indicate that these intermediates are similar in some respects, but different in others. Both are characterized by pronounced secondary structure, compact globularity, exposed hydrophobic surface area, and the absence of rigid side-chain packing, resembling the "molten globule" state. However, the burst phase intermediate shows more secondary structure, more exposed hydrophobic surface area, and more flexible side-chain packing than the equilibrium intermediate. Following the burst phase, there is a fast phase corresponding to folding of the monomer to a compact conformation. This is followed by rapid assembly to form the dimer. Neither of the equilibrium unfolding transitions are protein concentration dependent. The refolding kinetics are also not concentration dependent. This suggests that association of the subunits is not rate limiting for refolding, and that under equilibrium conditions, dissociation occurs in the region between the two unfolding transitions. Based upon the above results, schemes of unfolding and refolding of creatine kinase are proposed.

The compactness of ribonuclease A and reduced ribonuclease A

The compactness of ribonuclease A with intact disulfide bonds and reduced ribonuclease A was investigated by synchrotron small-angle X-ray scattering. The Rg values and the Kratky plots showed that non-reduced ribonuclease A maintain a compact shape with a Rg value of about 17.3 A in 8 M urea. The reduced ribonuclease A is more expanded, its Rg value is about 20 A in 50 mM Tris-HCl buffer at pH 8.1 containing 20 mM DTT. Further expansions of reduced ribonuclease A were observed in the presence of high concentrations of denaturants, indicating that reduced ribonuclease A is more expanded and is in neither a random coil [A. Noppert et al., FEBS Lett. 380 (1996) 179-182] nor a compact denatured state [T.R. Sosnick and J. Trewhella, Biochemistry 31 (1992) 8329-8335]. The four disulfide bonds keep ribonuclease A in a compact state in the presence of high concentrations of urea.

Expression of 5-lipoxygenase and 5-lipoxygenase-activating protein mRNAs in the peripheral blood leukocytes of asthmatics

Leukotrienes are a family of arachidonic acid metabolites with potent biological activities such as bronchoconstriction and leukocyte chemotaxis. Recent evidence has demonstrated that the 5-lipoxygenase (5-LO) and 5-lipoxygenase-activating protein (FALP) products of arachidonic acid metabolism, leukotriene C4, D4 and E4, were increased in the serum and the urine of asthmatic patients. Therefore, we examined the expression of 5-LO and FLAP mRNAs in the peripheral blood leukocytes (PBL) of 10 asthmatics and 10 controls. Both 5-LO and FLAP mRNAs of PBL in the asthmatic group were found to be significantly increased compared with those in the control group. These data suggest that up-regulation of 5-LO and FLAP mRNAs might be involved in the increased leukotriene synthesis and play an important role in the pathogenesis of asthma.

Imaging soft X-ray microscope at Rits Synchrotron Radiation Center

An imaging soft X-ray microscope with zone plates has been installed at Rits SR Center (Ritsumeikan University, Kusatsu, Japan). With this microscope, specimens were set in air, which made it possible to investigate the specimens without breaking the vacuum of the microscope. The specimens can be prefocused with an optical microscope. Dry and wet biospecimens in air were observed. A new optical system was designed to improve the resolution.

High-resolution X-ray topographic images of dislocations in a silicon crystal recorded using an X-ray zooming tube

A Be-window-type X-ray zooming tube is an X-ray digital imaging system whose magnification factor of X-ray images can be easily varied from 10 to 200, and whose spatial resolution is less than 0.5 micro m. This zooming tube was used as an imaging detector in double-crystal X-ray topography to obtain high-resolution images of dislocations in a silicon crystal. X-ray interference images of about 5 micro m were observed even though optimal performance of the X-ray zooming tube could not be achieved. The results indicate that the X-ray zooming tube might make a good detector for X-ray topography with minor improvements in its stage structure.

Studies on intracellular structures of COS cells by X-ray microscopy

COS-7 cells, fixed with glutaraldehyde, were studied using the transmission X-ray microscope at the electron storage ring BESSY, Berlin. The border of the cell, the nucleus, nucleoli and mitochondria of the cells were clearly visualized with the X-ray microscope. In addition, we found many X-ray dense granules preferentially located around the nucleus. Electron microscopy showed that numerous multivesicular bodies, whose structures belong to the endosome-lysosomal system, were present around the nucleus. The size and localization patterns of the X-ray dense granules were quite similar to those of multivesicular bodies. These results strongly suggest that the X-ray dense granules are multivesicular bodies.

Kinetic refolding of beta-lactoglobulin. Studies by synchrotron X-ray scattering, and circular dichroism, absorption and fluorescence spectroscopy

beta-Lactoglobulin (beta LG) is a predominantly beta-sheet protein with a markedly high helical propensity and forms non-native alpha-helical intermediate in the refolding process. We measured the refolding reaction of beta LG with various techniques and characterized the folding kinetics and the structure of the intermediate formed within the burst phase of measurements, i.e. the burst-phase intermediate. Time-resolved stopped-flow X-ray scattering measurements using the integral intensity of scattering show that beta LG forms a compact, globular structure within 30 ms of refolding. The averaged radius of gyration within 100 ms is only 1.1 times larger than that in the native state, ensuring that the burst-phase intermediate is compact. The presence of a maximum peak in a Kratky plot shows a globular shape attained within 100 ms of refolding. Stopped-flow circular dichroism, tryptophan absorption and fluorescence spectroscopy show that pronounced secondary structure regains rapidly in the burst phase with concurrent non-native alpha-helix formation, and that the subsequent compaction process is accompanied by annealing of non-native secondary structure and slow acquisition of tertiary structure. These findings strongly suggest that both compaction and secondary structure formation in protein folding are quite rapid processes, taking place within a millisecond time-scale. The structure of the burst-phase intermediate in beta LG refolding was characterized as having a compact size, a globular shape, a hydrophobic core, substantial beta-sheets and remarkable non-native alpha-helical structure, but little tertiary structure. These results suggest that both local interactions and non-local hydrophobic interactions are dominant forces early in protein folding. The interplay of local and non-local interactions throughout folding processes is important in understanding the mechanisms of protein folding.

Characterization and evolution of a gene encoding a Trimeresurus flavoviridis serum protein that inhibits basic phospholipase A2 isozymes in the snake's venom

The proteins that bind phospholipase A2 (PLA2) isozymes of Trimeresurus flavoviridis (habu snake, crotalinae) venom were fractionated from sera on four columns, each conjugated with one of four PLA2 isozymes. Five proteins, termed PLA2 inhibitors (PLI) I-V, were obtained as the binding components. The combinations of the binding components differed depending on the PLA2 isozymes. PLI-IV and PLI-V correspond to PLI-A and PLI-B, respectively, which were known to bind to a major [Asp49]PLA2, PLA2, and contained a segment similar to the carbohydrate-recognition domain of C-type lectins. PLI-I, which is a major component of inhibitory proteins against three basic PLA2 isozymes, PLA-B (a basic [Asp49]PLA2) and basic proteins I and II (both [Lys49]PLA2s), has been isolated, and its partial amino acid sequence has been determined. A cDNA encoding PLI-I was isolated from a T. flavoviridis liver cDNA library and sequenced. PLI-I cDNA encoded 200 amino acid residues, including a signal peptide of 19 amino acid residues. One sugar chain was predicted to occur at position 157. A gene coding for PLI-I was isolated. It is 9.6-kb long and consists of five exons and four introns. Comparison of the exon-intron structure of the PLI-I gene with those of genes encoding urokinase-type-plasminogen-activator receptor (uPAR), Ly-6, CD59 and neurotoxins showed that they have characteristic unit encoding approximately 90 amino acid residues, which is divided over two exons. This strongly suggests that the PLI-I gene belongs to the uPAR, Ly-6, CD59 and neurotoxin gene family. There are two types of structurally different inhibitors against PLA2 isozymes in T. flavoviridis serum with different evolutionary origins.

Unfolding of dimeric creatine kinase in urea and guanidine hydrochloride as measured using small angle X-ray scattering with synchrotron radiation

The denaturation of dimeric creatine kinase (CK) induced by urea and guanidine hydrochloride (GuHCl) has been studied by small angle X-ray scattering (SAXS), which is a direct way to measure the changes in the overall dimensions of a protein molecule. The radii of gyration (Rg) of CK are 29+/-0.4 angstroms in the native state and 46+/-1.5 angstroms in the unfolded state in either 8 M urea or 3 M GuHCl. The transition curves of urea denaturation derived from the Rg values and the zero angle intensity (I(0)) are similar to that from intrinsic fluorescence, indicating that the changes in the molecular shape, the tertiary structure and the dissociation of the subunits proceed simultaneously. In the case of GuHCl-induced denaturation, the dramatic increases both in Rg and in I(0) in 0.3-0.5 M GuHCl suggest clearly that soluble aggregates form at low GuHCl concentrations. The aggregates dissociate and the molecule unfolds at higher GuHCl concentrations. The results suggest that the mechanisms of CK denaturation in urea and in GuHCl are somewhat different and the intermediate in GuHCl denaturation can much more easily form soluble aggregates.

[Pheochromocytoma of the left retroperitoneal paraganglion associated with torsade de pointes: a case report]

A 54-year-old woman developed torsade de pointes with secondary QT prolongation due to hypokalemia and hypomagnesemia. Her serum K and Mg levels were 2.5 mEq/l and 1.5 mg/dl, respectively. This electrolyte imbalance was due to intentional overdosing of metolazone. Attacks of torsade de pointes occurred three times in the intensive care unit and were corrected by intravenous lidocaine administration. Her serum K level was corrected using KCl infusion, restoring the normal QT interval. Routine computed tomography found a left retroperitoneal paraganglioma. Urinary and serum catecholamine examination revealed extremely high values of epinephrine and norepinephrine. The diagnosis was pheochromocytoma in the left retroperitoneal paraganglion. The tumor which was removed measured 70 x 65 x 60 mm in size. Microscopic examination revealed the characteristic patterns of pheochromocytoma.

Structures of genes encoding phospholipase A2 inhibitors from the serum of Trimeresurus flavoviridis snake

Inhibitors (PLIs) against snake venom gland phospholipases A2 (PLA2s) have been found in their sera. A cDNA encoding a PLI from Trimeresurus flavoviridis (Tf, habu snake, Crotalinae) serum, cPLI-A, was isolated from the Tf liver cDNA library and sequenced. Northern blot analysis with cPLI-A showed that PLIs are expressed only in liver. Genes for PLIs, gPLI-A and gPLI-B, were isolated from the Tf genomic DNA library and their nucleotide (nt) sequences were determined. The genes consisted of four exons and three introns, and exon 4 encoded the carbohydrate recognition domain (CRD)-like motif. Comparison of the nt sequences between gPLI-A and gPLI-B showed that these genes are highly homologous, including introns, except that exon 3 is rich in nonsynonymous nt substitutions which are almost four times as frequent as synonymous nt substitutions. This evolutionary feature of PLI genes is different from that of venom gland PLA2 isozyme genes in which nonsynonymous nt substitutions are spread over the entire mature protein-coding region.

Downstream signaling molecules bind to different phosphorylated immunoreceptor tyrosine-based activation motif (ITAM) peptides of the high affinity IgE receptor

The cytoplasmic tails of both the beta and gamma subunits of the high affinity IgE receptor (FcepsilonRI) contain a consensus sequence termed the immunoreceptor tyrosine-based activation motif (ITAM). This motif plays a critical role in receptor-mediated signal transduction. Synthetic peptides based on the ITAM sequences of the beta and gamma subunits of FcepsilonRI were used to investigate which proteins associate with these motifs. Tyrosine-phosphorylated beta and gamma ITAM peptides immobilized on beads precipitated Syk, Lyn, Shc, Grb2, and phospholipase C-gamma1 from lysates of rat basophilic leukemia RBL-2H3 cells. Syk was precipitated predominantly by the tyrosine-diphosphorylated gamma ITAM peptide, but much less by the diphosphorylated beta ITAM peptide or by the monophosphorylated peptides. Phospholipase C-gamma1, Shc, and Grb2 were precipitated only by the diphosphorylated beta ITAM peptide. Non-phosphorylated ITAM peptides did not precipitate these proteins. In membrane binding assays, fusion proteins containing the Src homology 2 domains of phospholipase C-gamma1, Shc, Syk, and Lyn directly bound the tyrosine-phosphorylated ITAM peptides. Although the ITAM sequences of the beta and gamma subunits of FcepsilonRI are similar, once they are tyrosine-phosphorylated they preferentially bind different downstream signaling molecules. Tyrosine phosphorylation of the ITAM of the gamma subunit recruits and activates Syk, whereas the beta subunit may be important for the Ras signaling pathway.

Protein globularization during folding. A study by synchrotron small-angle X-ray scattering

Various conformational states of polypeptide chains were investigated by synchrotron small-angle X-ray scattering (SAXS). SAXS patterns of proteins and model polypeptides in globular states (native and "molten globule") and in non-globular states (unfolded protein as well as randomly coiled, partially alpha-helical and partially beta-structural synthetic polypeptides) were analyzed in terms of Guinier and Kratky plots. Large differences in the SAXS pattern have been found between globular and non-globular conformations of the polypeptide chains, and they have been interpreted in terms of differences in the shape and size of the globular and non-globular scatterers with the same molecular mass. The equilibrium and time-resolved unfolding curves of bovine carbonic anhydrase and yeast phosphoglycerate kinase were monitored by integrated SAXS intensity, and were found to be coincident with the curves measured by other physicochemical techniques, such as tryptophan fluorescence and peptide circular dichroism spectra. The intermolecular association of the protein "molten globule"-like intermediates accumulated during the guanidine hydrochloride-induced unfolding of bovine carbonic anhydrase has been investigated by various SAXS parameters. It has been shown that the integrated SAXS intensity is much less sensitive to the protein intermolecular association than the zero angle intensity and the radius of gyration. We propose the integrated SAXS intensity as a global parameter which is particularly appropriate for fast kinetic studies of protein coil to globule transitions. Time-resolved refolding curves of the above proteins were monitored by the integrated SAXS intensity to investigate the globularization process in protein folding. Two fast kinetic processes for bovine carbonic anhydrase and two fast (each within two seconds) as well as two slow (within 500 seconds) kinetic processes for yeast phosphoglycerate kinase have been recorded. The kinetic processes reflect both protein intramolecular globularization and its intermolecular association.