Stachyose extract from Rehmannia glutinosa Libosch. to lower plasma glucose in normal and diabetic rats by oral administration

The hypoglycemic effects of water extract and stachyose extract (Part III) from Rehmannia glutinosa Libosch. were investigated in this paper by oral administration to normal, glucose- and adrenaline-induced hyperglycemic and alloxan-induced diabetic rats. The results showed that Part III had the effect of lowering fasted plasma glucose level and partially preventing hyperglycemia induced by glucose (2.5 g x kg(-1), i.p.) and adrenaline (300 microg x kg(-1), i.p.), respectively, but no obvious dose-dependent effect was found when it was administered at the doses of 100, 200 and 400 mg x kg(-1) for 6 days, i.g. In alloxan-induced diabetic rats, Part III (200 mg x kg(-1) for 15 days, i.g.) gave a significant decrease in blood glucose level. The results suggested that Part III, which is mainly composed of stachyose from Rehmannia glutinosa Libosch., had a significant hypoglycemic effect in glucose- and adrenaline-induced hyperglycemic and alloxan-induced diabetic rats.

Tests of linkage and association of the COL1A2 gene with bone phenotypes' variation in Chinese nuclear families

In the present study, we simultaneously test linkage and/or association of the collagen type I alpha 2 (COL1A2) gene with bone mineral density (BMD) and bone area. A total of 1280 subjects from 407 Chinese nuclear families (including both parents and their daughters) were genotyped for an intragenic marker MspI in the COL1A2 gene. BMD and bone area at the lumbar spine and hip were measured by dual-energy X-ray absorptiometry. Applying the QTDT (quantitative transmission disequilibrium test) program, we performed tests for population stratification, within-family association (via transmission disequilibrium test), total association, linkage, and linkage while modeling association. Significant or marginal within-family associations were found with BMD at the lumbar spine (P = 0.013), trochanter (P = 0.004), and total hip (P = 0.053) and with bone area at the intertrochanteric region (P = 0.024) and total hip (P = 0.048). The positive associations were confirmed in permutations except for bone area at total hip (P > 0.10). A small proportion (<1%) of the population variance of bone phenotypes can be explained by the MspI polymorphism; however, it may be underestimated given the significant population stratification detected in our sample. Due to the limited number of sib pairs in this sample, we did not find evidence of linkage. In summary, the MspI polymorphism is likely to be in linkage disequilibrium with a nearby functional mutation affecting BMD and bone area.

No evidence for linkage and/or association of human alpha2-HS glycoprotein gene with bone mineral density variation in Chinese nuclear families

Osteoporosis is an important health problem in the world. Alpha2-HS glycoprotein (AHSG) is involved in bone formation and metabolism and has been considered as an important candidate gene for osteoporosis. In this study, we simultaneously tested linkage and/or association of the AHSG gene with the variation of bone mineral density (BMD), an important risk factor for osteoporosis. A sample of 1,260 subjects from 401 Chinese nuclear families (including both parents and their daughters) were studied. The daughters' ages ranged from 20 to 45 years. All the subjects were genotyped by PCR-RFLP (polymerase chain reaction-restriction fragment length polymorphism) at polymorphic Sac I site inside the exon 7 of the AHSG gene. This polymorphism involves a nucleotide substitution of C to G at the middle nucleotide of the codon at amino acid position 238, resulting in the replacement of threonine (ACC) with serine (AGC). BMD was measured at the lumbar spine and hip region by dual-energy X-ray absorptiometry (DXA). Using the QTDT (quantitative trait transmission disequilibrium test), we found no significant results for association or linkage between the AHSG gene and BMD variation at the spine or hip. Our data provided no evidence to support the AHSG gene as a quantitative trait locus (QTL) for the BMD variation in a Chinese population.

Opposing actions of protein kinase A and C mediate Hebbian synaptic plasticity

A compartmental nerve-muscle tissue culture system expresses Hebbian activity-dependent synapse modulation. Protein kinase C (PKC) mediates a heterosynaptic loss of efficacy, and we now show that protein kinase A (PKA) is involved in homosynaptic stabilization. Both work through postsynaptic changes in the acetylcholine receptor (AChR) as measured electrophysiologically and by imaging techniques.

Structure of the C-domain of human cardiac troponin C in complex with the Ca2+ sensitizing drug EMD 57033

Ca(2+) binding to cardiac troponin C (cTnC) triggers contraction in heart muscle. In heart failure, myofilaments response to Ca(2+) are often altered and compounds that sensitize the myofilaments to Ca(2+) possess therapeutic value in this syndrome. One of the most potent and selective Ca(2+) sensitizers is the thiadiazinone derivative EMD 57033, which increases myocardial contractile function both in vivo and in vitro and interacts with cTnC in vitro. We have determined the NMR structure of the 1:1 complex between Ca(2+)-saturated C-domain of human cTnC (cCTnC) and EMD 57033. Favorable hydrophobic interactions between the drug and the protein position EMD 57033 in the hydrophobic cleft of the protein. The drug molecule is orientated such that the chiral group of EMD 57033 fits deep in the hydrophobic pocket and makes several key contacts with the protein. This stereospecific interaction explains why the (-)-enantiomer of EMD 57033 is inactive. Titrations of the cCTnC.EMD 57033 complex with two regions of cardiac troponin I (cTnI(34-71) and cTnI(128-147)) reveal that the drug does not share a common binding epitope with cTnI(128-147) but is completely displaced by cTnI(34-71). These results have important implications for elucidating the mechanism of the Ca(2+) sensitizing effect of EMD 57033 in cardiac muscle contraction.

[Analysis of P interval dispersion and its correlative factors among Chinese]

OBJECTIVE

To establish mean value of P interval dispersion of 12-lead simultaneous body surface electrocardiogram in healthy Chinese and to analyse its correlative factors.

METHODS

12-lead simultaneous body surface electrocardiogram data were taken from 2078 healthy Chinese aged from 1 to 87 [mean (39.4 +/- 17.3)] years with SR-1000A automated electrocardiography made by Zhongshan, Guangdong province. These data were stored in the floppy disk.

RESULTS

Mean value of Pmax, Pmin, Pd and Pcd seemed to be prolonged, and Pcmax, Pcmin to be shortened with increasing of age, but there was no significant difference between age and sex. Mean value of Pmax of the all subjects (1-87 years) was (109.85 +/- 7.88) ms, Pmin (80.97 +/- 11.42) ms, Pcmax (123.13 +/- 12.00) ms, Pcmin (90.85 +/- 14.40) ms, Pd (28.89 +/- 10.74) ms, Pcd (32.39 +/- 12.10) ms; mean values of Pmax, Pmin, Pd and Pcd among the children of 1-14 years were (101.54 +/- 9.49) ms, (76.85 +/- 10.19) ms, (24.82 +/- 7.51) ms and (31.10 +/- 9.89) ms, respectively; 77.04% of Pmax was in II lead and 14.39% in V5 lead, 74.69% of Pmin was in V1 lead and 7.84% in V2 lead.

CONCLUSION

The mean value of Pmax is 96-120 ms, Pd 8-50 ms and Pcd 10-56 ms among healthy Chinese. Pd is not significantly related with heart rate, age and sex.

Antagonizing effect of AP-1 on glucocorticoid induction of urea cycle enzymes: a study of hyperammonemia in carnitine-deficient, juvenile visceral steatosis mice

Hyperammonemia is one of the major symptoms of primary carnitine deficiency. Carnitine-deficient juvenile visceral steatosis (JVS) mice show hyperammonemia during the weaning period. We have found that all of the urea cycle enzyme genes are suppressed and that N-acetylglutamate, an allosteric activator of the first step enzyme of the urea cycle, carbamoyl phosphate synthetase I (CPS), is not deficient in the liver of JVS mice. Induction of the urea cycle enzymes by glucocorticoid in rat primary cultured hepatocytes was suppressed by the addition of long-chain fatty acids. The suppression of the urea cycle enzyme genes in vivo and in vitro is accompanied by stimulated AP-1 DNA-binding activity. However, mRNA of phosphoenolpyruvate carboxykinase, one of the gluconeogenic enzymes which responds to glucocorticoid, is further stimulated by the addition of fatty acid. From these results, we postulate that protein-protein interaction between glucocorticoid receptors and AP-1 is not the major mechanism of suppression, but that AP-1 causes the suppression through a cis-element on the gene. After cloning promoter and enhancer regions of the mouse CPS gene and comparing rat and mouse, we found that an AP-1 site was present just 3'-downstream of the minimal essential enhancer fragment previously described. We also found that the presence of an AP-1 site in reporter gene constructs resulted in suppression of the reporter genes in the liver of carnitine-deficient JVS mice and suppression of glucocorticoid induction by long-chain fatty acid in cultured hepatocytes.

Identification of two novel mutations in the SLC25A13 gene and detection of seven mutations in 102 patients with adult-onset type II citrullinemia

Adult-onset type II citrullinemia (CTLN2) is characterized by a liver-specific deficiency of argininosuccinate synthetase (ASS) protein. We have recently identified the gene responsible for CTLN2, viz., SLC25A13, which encodes a calcium-binding mitochondrial carrier protein, designated citrin, and found five mutations of the SLC25A13 gene in CTLN2 patients. In the present study, we have identified two novel mutations, 1800ins1 and R605X, in SLC25A13 mRNA and the SLC25A13 gene. Diagnostic analysis for the seven mutations in 103 CTLN2 patients diagnosed by biochemical and enzymatic studies has revealed that 102 patients had one or two of the seven mutations and 93 patients were homozygotes or compound heterozygotes. These results indicate that CTLN2 is caused by an abnormality in the SLC25A13 gene, and that our criteria for CTLN2 before DNA diagnosis are correct. Five of 22 patients from consanguineous unions have been shown to be compound heterozygotes, suggesting a high frequency of the mutated genes. The frequency of homozygotes is calculated to be more than 1 in 20,000 from carrier detection (6 in 400 individuals tested) in the Japanese population. We have detected no cross-reactive immune materials in the liver of CTLN2 patients with any of the seven mutations by Western blot analysis with anti-human citrin antibody. From these findings, we hypothesize that CTLN2 is caused by a complete deletion of citrin, although the mechanism of ASS deficiency is still unknown.

Energetics of the induced structural change in a Ca2+ regulatory protein: Ca2+ and troponin I peptide binding to the E41A mutant of the N-domain of skeletal troponin C

Structural studies have shown that the regulatory domains of skeletal and cardiac troponin C (sNTnC and cNTnC) undergo different conformational changes upon Ca(2+) binding; sNTnC "opens" with a large exposure of the hydrophobic surface, while cNTnC retains a "closed" conformation similar to that in the apo state. This is mainly due to the fact that there is a defunct Ca(2+)-binding site I in cNTnC. Despite the striking difference, the two proteins bind their respective troponin I (TnI) regions (sTnI(115-131) and cTnI(147-163), respectively) in a similar open fashion. Thus, there must exist a delicate energetic balance between Ca(2+) and TnI binding and the accompanying conformational changes in TnC for each system. To understand the coupling between Ca(2+) and TnI binding and the concomitant structural changes, we have previously engineered an E41A mutant of sNTnC and demonstrated that this mutation drastically reduced the Ca(2+)-binding affinity of site I in sNTnC, and as a result, E41A-sNTnC remains closed in the Ca(2+)-bound state. In the present work, we investigated the interaction of E41A-sNTnC with the sTnI(115-131) peptide and found that the peptide binds to the Ca(2+)-saturated E41A-sNTnC with a 1:1 stoichiometry and a dissociation constant of 300 +/- 100 microM. The peptide-induced chemical shift changes resemble those of Ca(2+) binding to sNTnC, suggesting that sTnI(115-131) induces the "opening" of E41A-sNTnC. In addition, the binding of sTnI(115-131) appears to be accompanied by a conformational change in site I of E41A-sNTnC so that the damaged regulatory site can bind Ca(2+) more tightly. Without Ca(2+), sTnI(115-131) only interacts with E41A-sNTnC nonspecifically. When Ca(2+) is titrated into E41A-sNTnC in the presence of sTnI(115-131), the Ca(2+)-binding affinity of site I was enhanced by approximately 5-fold as compared to when sTnI(115-131) was not present. These observations suggest that the binding of Ca(2+) and TnI is intimately coupled to each other. Together with our previous studies on Ca(2+) and TnI peptide binding to sNTnC and cNTnC, these results allow us to dissect the mechanism and energetics of coupling of ligand binding and structural opening intricately involved in the regulation of skeletal and cardiac muscle contraction.

Protein kinase C-mediated changes in synaptic efficacy at the neuromuscular junction in vitro: the role of postsynaptic acetylcholine receptors

Activation of a mouse in vitro neuromuscular synapse produces a reduction in synaptic efficacy which is greater for nonactivated than for activated inputs to the myotubes. This has been shown to require thrombin and thrombin receptor activation and to involve a protein kinase C (PKC)-mediated step. We show in the present work that phorbol ester activation of PKC produces physiological loss of synapses in a time- and dose-related manner. We observe, using quantitative imaging methods, a parallel loss of acetylcholine receptors (AChR) from synaptically functional neurite-associated receptor aggregates in nerve-muscle cocultures. Biochemical measurements of total AChR show that PKC activation reduces both AChR stability (increases receptor loss) and receptor insertion into the surface membrane. Taken together, the data suggest that PKC activation decreases the stability of AChR aggregates in the muscle surface membrane. We conclude that PKC plays a crucial role in activity-dependent synapse reduction and does so, at least in part, by altering AChR stability.

Scattering of antiplane shear waves by a circular cylinder in a traction-free plate

Following a well-established formula used by many researchers, the scattering of an anti-plane shear wave by an infinite elastic cylinder of arbitrary relative radius centered in a traction-free two-dimensional isotropic plate has been examined. The plate is divided into three regions by introducing two imaginary planes located symmetrically away from the surface of the cylinder and perpendicular to surfaces of the plate. The wave field is expanded into cylinder wave modes in the central bounded region containing the cylinder, while the fields in the other two outer regions are expanded into plate wave modes. A system of equations determining the expansion coefficients is obtained according to the traction-free boundary conditions on the plate walls and the stress and displacement continuity conditions across the imaginary planes. By taking an appropriate finite number of terms of the infinite expansion series and a few selected points on the two properly chosen virtual planes and the surfaces of the plate through convergence and precision tests, a matrix equation to numerically evaluate the expansion coefficients is found. The method of how to choose the locations of the imaginary planes and the terms of the expansion series as well as the points on each respective boundary is given in Sec. III in detail. Curves of the reflection and transmission coefficients against the relative radius of the cylinder in welded and slip or cracked interfacial conditions are shown. Analysis on the contrast variations of the reflection and transmission coefficients for a cylinder in bonded and debonded interfacial situations is made. The relative errors estimated by the deviation of the numerical results from the principle of the conservation of energy are found to be less than 2%.

Interaction of cardiac troponin C with Ca(2+) sensitizer EMD 57033 and cardiac troponin I inhibitory peptide

The binding of Ca(2+) to cardiac troponin C (cTnC) triggers contraction in cardiac muscle. In diseased heart, the myocardium is often desensitized to Ca(2+), leading to weak cardiac contractility. Compounds that can sensitize cardiac muscle to Ca(2+) would have potential therapeutic value in treating heart failure. The thiadiazinone derivative EMD 57033 is an identified 'Ca(2+) sensitizer', and cTnC is a potential target of the drug. In this work, we used 2D ¿(1)H, (15)N¿-HSQC NMR spectroscopy to monitor the binding of EMD 57033 to cTnC in the Ca(2+)-saturated state. By mapping the chemical shift changes to the structure of cTnC, EMD 57033 is found to bind to the C-domain of cTnC. To test whether EMD 57033 competes with cardiac TnI (cTnI) for cTnC and interferes with the inhibitory function, we examined the interaction of cTnC with an inhibitory cTnI peptide (residues 128-147, cIp) in the absence and presence of EMD 57033, respectively. cTnC was also titrated with EMD 57033 in the presence of cIp. The results show that although both the drug and cIp interact with the C-domain of cTnC, they do not displace each other, suggesting noncompetitive binding sites for the two targets. Detailed chemical shift mapping of the binding sites reveals that the regions encompassing helix G-loop IV-helix H are more affected by EMD 57033, while residues located on helix E-loop III-helix F and the linker between sites III and IV are more affected by cIp. In both cases, the binding stoichiometry is 1:1. The binding affinities for the drug are 8.0 +/- 1.8 and 7.4 +/- 4.8 microM in the absence and presence of cIp, respectively, while those for the peptide are 78.2 +/- 10.3 and 99.2 +/- 30.0 microM in the absence and presence of EMD 57033, respectively. These findings suggest that EMD 57033 may exert its positive inotropic effect by not directly enhancing Ca(2+) binding to the Ca(2+) regulatory site of cTnC, but by binding to the structural domain of cTnC, modulating the interaction between cTnC and other thin filament proteins, and increasing the apparent Ca(2+) sensitivity of the contractile system.

[Investigation report on the inherited characteristics of congenital preauricular fistula]

OBJECTIVE

To further analyse the inherited characteristics of congenital preauricular fistula.

METHOD

Analysed the familial incidence of 8 cases out of 73 (95 ears) which had been cured and investigated in our hospital in the past 16 years.

RESULT

The disease could be inherited from either parents; It was of autosomal dominant in type; It was not sex-linked; They inherited either in the same side or both sides; It could be transferred between every other generations.

CONCLUSION

All these were resulted in that congenital preauricular fistula was autosomal dominant inheritance with incomplete dominant.

Role of the structural domain of troponin C in muscle regulation: NMR studies of Ca2+ binding and subsequent interactions with regions 1-40 and 96-115 of troponin I

The interaction between the calcium binding and inhibitory components of troponin is central to the regulation of muscle contraction. In this work, two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance (2D-¿1H,15N¿-HSQC NMR) spectroscopy was used to determine the stoichiometry, affinity, and mechanisms for binding of Ca2+ and two synthetic TnI peptides [TnI1-40 (or Rp40) and TnI96-115] to the isolated C-domain of skeletal troponin C (CTnC). The Ca2+ titration revealed that 2 equiv of Ca2+ binds to sites III and IV of CTnC with strong positive cooperativity and high affinity [dissociation constant (KD) </= 0.1 microM]. In this process, CTnC folds from a largely unstructured state to a compact domain capable of interacting with TnI. Titration of CTnC x 2Ca2+ with Rp40 occurs with a 1:1 stoichiometry and a KD of 2 +/- 1 microM. Titration of CTnC x 2Ca2+ with a peptide corresponding to the inhibitory region of TnI (TnI96-115) also reveals a 1:1 ratio, but weaker affinity (KD = 47 +/- 7 microM). Both Rp40- and TnI96-115-induced backbone amide chemical shift changes of CTnC x 2Ca2+ are similarly distributed along the sequence, indicating that these two regions of TnI may compete for the same binding site on CTnC x 2Ca2+. The changes induced by Rp40 are much larger, however, and define the interaction sites on TnC and regions where the flexibility of hinge and terminal residues is altered. To investigate the possibility of direct competition, TnI(96-115) was titrated into the CTnC x 2Ca(2+) x Rp40 complex, whereas Rp40 was titrated into the CTnC x 2Ca2+. TnI96-115 complex. The results show that Rp40 can displace TnI96-115 completely, while TnI96-115 has no effect on CTnC x 2Ca2+ x Rp40. Recent proposals for the mechanism of muscle regulation [Tripet, B. P., Van Eyk, J. E., and Hodges, R. S. (1997) J. Mol. Biol. 271, 728-750] suggest that the N-terminal and inhibitory regions of TnI competitively bind the structural domain of TnC. The findings presented here indicate that additional factors, such as interactions between the N-domain of TnC with the C-domain of TnI or the C-domain of TnT, are required, if the inhibitory region is going to successfully compete for the structural domain of TnC.

[Electrocardiographic QRS waves of healthy Chinese population with different ages and sexes]

OBJECTIVE

To develop a normal electrocardiographic QRS wave standard in Chinese population with different ages and sexes.

METHODS

Fourteen leads electrocardiographic QRS waves of 4,322 Chinese healthy subjects aged from birth to 85 years old divided into 11 age-groups were analysed and studied.

RESULTS

There were highly significant differences in QRS amplitudes and cardiac electric axes of different ages and sexes. The changes of QRS amplitudes which increased and decreased with advancing age were usually earlier in female than in male. Comparing with QRS waves there were higher QRS amplitudes in girls than in boys in the newborn period; however, it is higher in male than in female in puberty and middle-aged persons. The sex difference was not obvious relatively in small children and the aged. There was significant difference in QRS amplitudes when electrocardiograms of Chinese people compared with those of Westerners.

CONCLUSION

A Chinese normal electrocardiographic QRS standard established according to different ages and sexes may be applied clinically.

Aberrations of ammonia metabolism in ornithine carbamoyltransferase-deficient spf-ash mice and their prevention by treatment with urea cycle intermediate amino acids and an ornithine aminotransferase inactivator

Sparse fur with abnormal skin and hair (spf-ash) mice are deficient in ornithine carbamoyltransferase (OCT) activity, but their OCT protein is kinetically normal. We administered ammonium chloride to spf-ash mice, in order to analyze ammonia metabolism and to find a rationale for the therapy of OCT deficiency. Ammonia concentration in the liver of spf-ash mice increased to a level much higher than in the control. Ammonium chloride injection caused an increase in ornithine (Orn) 5 min after injection and an increase in the sum of Orn, citrulline (Cit) and arginine (Arg) for at least 15 min in the liver of control mice, but no increase in Orn, Cit and Arg in the liver of spf-ash mice. Treatment of spf-ash mice with Arg 5-20 min prior to the injection of ammonium chloride kept the hepatic ammonia concentration at a level comparable to that without the load. A significant reciprocal relationship between ammonia and Orn concentrations in the liver of spf-ash mice 5 min after an ammonium chloride load with or without Arg strongly suggests that ammonia disposal is dependent on the supply of Orn. In spf-ash mice loaded with tryptone as a nitrogen source, Arg supplementation showed a dramatic decrease in urinary orotic acid excretion in a dose-dependent manner. Similar effects were observed with Cit and Orn at the same dose, and a long-lasting effect with an ornithine aminotransferase inactivator, 5-(fluoromethyl)ornithine, at a much lower dose. The rate of urea formation in liver perfused with ammonium chloride was lower in spf-ash mice than in controls, but with the addition of Orn to the medium it increased to a similar level in control and spf-ash mice. These results indicate that OCT is not saturated with Orn in vivo under physiological conditions and that the administration or enrichment of the urea cycle intermediate amino acids enhances the OCT reaction so that the ammonia metabolism of OCT-deficient spf-ash mice is at least partially normalized.

Binding of cardiac troponin-I147-163 induces a structural opening in human cardiac troponin-C

The interaction of troponin-C (TnC) with troponin-I (TnI) plays a central role in skeletal and cardiac muscle contraction. We have recently shown that the binding of Ca2+ to cardiac TnC (cTnC) does not induce an "opening" of the regulatory domain in order to interact with cTnI [Sia, S. K., et al. (1997) J. Biol. Chem. 272, 18216-18221; Spyracopoulos et al. (1997) Biochemistry 36, 12138-12146], which is in contrast to the regulatory N-domain of skeletal TnC (sTnC). This implies that the mode of interaction between cTnC and cTnI may be different than that between sTnC and sTnI. In sTnI, a region downstream from the inhibitory region (residues 115-131) has been shown to bind the exposed hydrophobic pocket of Ca2+-saturated sNTnC [McKay, R. T., et al. (1997) J. Biol. Chem. 272, 28494-28500]. The present study demonstrates that the corresponding region in cTnI (residues 147-163) binds to the regulatory domain of cTnC only in the Ca2+-saturated state to form a 1:1 complex, with an affinity approximately six times weaker than that between the skeletal counterparts. Thus, while Ca2+ does not cause opening, it is required for muscle regulation. The solution structure of the cNTnC.Ca2+.cTnI147-163 complex has been determined by multinuclear multidimensional NMR spectroscopy. The structure reveals an open conformation for cNTnC, similar to that of Ca2+-saturated sNTnC. The bound peptide adopts a alpha-helical conformation spanning residues 150-157. The C-terminus of the peptide is unstructured. The open conformation for Ca2+-saturated cNTnC in the presence of cTnI (residues 147-163) accommodates hydrophobic interactions between side chains of the peptide and side chains at the interface of A and B helices of cNTnC. Thus the mechanistic differences between the regulation of cardiac and skeletal muscle contraction can be understood in terms of different thermodynamics and kinetics equilibria between essentially the same structure states.

The NMR angle on troponin C

The calcium-induced structural changes in the skeletal muscle regulatory protein troponin C involve a transition from a closed to an open structure with the concomitant exposure of a large hydrophobic interaction site for target proteins. NMR solution structural studies have served to define this conformational change and elucidate the mechanism of the linkage between calcium binding and the induced structural changes. These structural movements are described in terms of interhelical angles in these largely helical proteins. Oddly, the most recent structure of the cardiac system challenges the central paradigm because the calcium-bound structures are not open. The kinetics, energetics, and dynamics of these proteins have also been investigated using NMR.

Dynamics and thermodynamics of the regulatory domain of human cardiac troponin C in the apo- and calcium-saturated states

The contraction of cardiac and skeletal muscles is triggered by the binding of Ca2+ to their respective troponin C (TnC) proteins. Recent structural data of both cardiac and skeletal TnC in both the apo and Ca2+ states have revealed that the response to Ca2+ is fundamentally different for these two proteins. For skeletal TnC, binding of two Ca2+ to sites 1 and 2 leads to large changes in the structure, resulting in the exposure of a hydrophobic surface. For cardiac TnC, Ca2+ binds site 2 only, as site 1 is inactive, and the structures show that the Ca2+-induced changes are much smaller and do not result in the exposure of a large hydrophobic surface. To understand the differences between regulation of skeletal and cardiac muscle, we have investigated the effect of Ca2+ binding on the dynamics and thermodynamics of the regulatory N-domain of cardiac TnC (cNTnC) using backbone 15N nuclear magnetic resonance relaxation measurements for comparison to the skeletal system. Analysis of the relaxation data allows for the estimation of the contribution of changes in picosecond to nanosecond time scale motions to the conformational entropy of the Ca2+-binding sites on a per residue basis, which can be related to the structural features of the sites. The results indicate that binding of Ca2+ to the functional site in cNTnC makes the site more rigid with respect to high-frequency motions; this corresponds to a decrease in the conformational entropy (TdeltaS) of the site by 2.2 kcal mol(-1). Although site 1 is defunct, binding to site 2 also decreases the conformational entropy in the nonfunctional site by 0.5 kcal mol(-1). The results indicate that the Ca2+-binding sites in the regulatory domain are structurally and energetically coupled despite the inability of site 1 to bind Ca2+. Comparison between the cardiac and skeletal isoforms in the apo state shows that there is a decrease in conformational entropy of 0.9 kcal mol(-1) for site 1 of cNTnC and little difference for site 2.

Development of a three-dimensional topographic map display for capillary electrophoresis/mass spectrometry with an ion trap/reflectron time-of-flight mass spectrometer detector: applications to tryptic digests of isoforms of myelin basic protein

A three-dimensional (3-D) contour map format has been developed to display the large amount of data continuously collected throughout an on-line capillary separation using an ion trap storage/reflectron time-of-flight detector (IT/reTOF). The resulting data are displayed on a single computer screen with a mass-to-charge ratio value-elution time-intensity representation. The intensity of various components is represented by 16 different colors so that the mass-to-charge ratio value, the elution time, and the intensity can be conveniently determined for each component. In addition, the mass spectrum and total ion chromatogram or total ion electropherogram (TIE) are shown on the same screen as the 3-D map that enables the correlation of a single spot in the 3-D map to the peaks in the TIE and the corresponding mass spectrum. The 3-D map has been used to identify various posttranslational modification sites of bovine myelin basic protein charge isomers, where the datafiles of tryptic digests of proteins analyzed by capillary electrophoresis/mass spectrometry were processed by this software and a comparison could be performed among the isoforms. The feature of in-screen integration over both the separation domain and the mass domain makes the acquisition of the selected ion chromatogram very convenient and greatly improves the ability to detect modified components present in low amounts.

Determination of the sites of posttranslational modifications in the charge isomers of bovine myelin basic protein by capillary electrophoresis-mass spectroscopy

The posttranslational modifications in each of the 18.5 kDa bovine myelin basic protein charge isomers C-1 to C-6 have been determined by the use of capillary electrophoresis-mass spectroscopy. The pattern of modifications is viewed as being unique to each charge isomer and is thought to reflect a specific placement and function for each isomer in the myelin membrane. Several of the sites of posttranslational phosphorylation were found to differ from a number of the reported sites that were phosphorylated in vitro by various kinases. These differences suggest that an extremely cautious approach be taken in identifying in vivo posttranslationally modified amino acid residues from residues that have been modified in vitro by various kinases. We have identified the following posttranslationally phosphorylated and deamidated, modified sites in the bovine MBP components C1-C6. C1 has no modification; C2 represents a deamidation of Gln 146; in C3, Thr 97 and Ser 164 are phosphorylated; in C4, Ser 54, Thr 97, and Ser 160 are phosphorylated; in C5 Ser 7, Ser 54, Thr 97, and Ser 164 are phosphorylated; and in C6, Ser 7, Ser 54, Thr 97, Ser 160, and Ser 164 are phosphorylated.

On-line analysis by capillary separations interfaced to an ion trap storage/reflectron time-of-flight mass spectrometer

The interface of high-resolution capillary separation methods to time-of-flight mass spectrometry (TOF-MS) has generated considerable interest since TOF can provide the rapid and sensitive detection required by high resolution separations. In recent years, our laboratory has developed a variety of high-resolution capillary separation methods interfaced to TOF-MS via an ion trap storage/reflectron time-of-flight (IT/reTOF) instrument. Using this hybrid configuration, detection of fast separations at very low detection levels has been successfully performed for on-line separations of peptides and protein digests using electrospray ionization. In this report, we review the current status in our laboratory of interfacing high-performance liquid chromatography, capillary electrophoresis, and capillary electrochromatography to an IT/reTOF-MS instrument and various applications that have been developed involving this technology.

Retroviral transduction of human CD34+ umbilical cord blood progenitor cells with a mutated dihydrofolate reductase cDNA

Umbilical cord blood cells (UCB) have become a major target population for experimental and clinical studies using transfer of genes involved in inborn enzymatic diseases. Cord blood contains hematopoietic progenitor cells at a high frequency, and expanding these cells ex vivo generates sufficient numbers of hematopoietic precursors for transplantation into adults, e.g., as supportive treatment. As clinical reports about retroviral transduction into UCB cells have not been as encouraging as the first preclinical data, we have established a retroviral transduction system that allows expansion and selection of hematopoietic progenitor cells from UCB. CD34-enriched UCB cells were transduced with a retroviral vector encoding a mutated dihydrofolate reductase cDNA that confers MTX resistance. We observed increased resistance to MTX in transduced granulocyte macrophage-colony forming units (CFU-GM) after co-culture of CD34+ UCB cells with the virus-producing cell line, or after incubation with virus-containing supernatant. The supernatant-based transduction protocol included a prestimulation with recombinant interleukin-1 (rhIL-1), rhkit-ligand, and rhIL-3 to increase the percentage of cells in S phase to greater than 50%. Using this protocol we measured a 72-fold expansion of CFU-GM and a 2.5-fold selective advantage of transduced versus nontransduced progenitor cells after exposure to low-dose methotrexate in liquid culture. Polymerase chain reaction analysis revealed integration of proviral DNA into the majority of transduced colonies before and after ex vivo expansion. The retroviral vector and transduction protocol reported here provides an experimental system for selection and expansion of retrovirally transduced progenitor/stem cells from UCB that may help improve the efficiency of current clinical gene therapy strategies.

Structural details of a calcium-induced molecular switch: X-ray crystallographic analysis of the calcium-saturated N-terminal domain of troponin C at 1.75 A resolution

We have solved and refined the crystal and molecular structures of the calcium-saturated N-terminal domain of troponin C (TnC) to 1.75 A resolution. This has allowed for the first detailed analysis of the calcium binding sites of this molecular switch in the calcium-loaded state. The results provide support for the proposed binding order and qualitatively, for the affinity of calcium in the two regulatory calcium binding sites. Based on a comparison with the high-resolution apo-form of TnC we propose a possible mechanism for the calcium-mediated exposure of a large hydrophobic surface that is central to the initiation of muscle contraction within the cell.

NMR studies of Ca2+ binding to the regulatory domains of cardiac and E41A skeletal muscle troponin C reveal the importance of site I to energetics of the induced structural changes

Ca2+ binding to the N-domain of skeletal muscle troponin C (sNTnC) induces an "opening" of the structure [Gagné, S. M., et al. (1995) Nat. Struct. Biol. 2, 784-789], which is typical of Ca2+-regulatory proteins. However, the recent structures of the E41A mutant of skeletal troponin C (E41A sNTnC) [Gagné, S. M., et al. (1997) Biochemistry 36, 4386-4392] and of cardiac muscle troponin C (cNTnC) [Sia, S. K., et al. (1997) J. Biol. Chem. 272, 18216-18221] reveal that both of these proteins remain essentially in the "closed" conformation in their Ca2+-saturated states. Both of these proteins are modified in Ca2+-binding site I, albeit differently, suggesting a critical role for this region in the coupling of Ca2+ binding to the induced structural change. To understand the mechanism and the energetics involved in the Ca2+-induced structural transition, Ca2+ binding to E41A sNTnC and to cNTnC have been investigated by using one-dimensional 1H and two-dimensional {1H,15N}-HSQC NMR spectroscopy. Monitoring the chemical shift changes during Ca2+ titration of E41A sNTnC permits us to assign the order of stepwise binding as site II followed by site I and reveals that the mutation reduced the Ca2+ binding affinity of the site I by approximately 100-fold [from KD2 = 16 microM [sNTnC; Li, M. X., et al. (1995) Biochemistry 34, 8330-8340] to 1.3 mM (E41A sNTnC)] and of the site II by approximately 10-fold [from KD1 = 1.7 microM (sNTnC) to 15 microM (E41A sNTnC)]. Ca2+ titration of cNTnC confirms that cNTnC binds only one Ca2+ with a determined dissociation constant KD of 2.6 microM. The Ca2+-induced chemical shift changes occur over the entire sequence in cNTnC, suggesting that the defunct site I is perturbed when site II binds Ca2+. These measurements allow us to dissect the mechanism and energetics of the Ca2+-induced structural changes.