The WW1 Domain Enhances Autoinhibition in Smurf Ubiquitin Ligases

Downregulation of ubiquitin (Ub) ligase activity prevents premature ubiquitination and is critical for cellular homeostasis. Nedd4 Ub ligases share a common domain architecture and yet are regulated in distinct ways through interactions of the catalytic HECT domain with the N-terminal C2 domain or the central WW domain region. Smurf1 and Smurf2 are two highly related Nedd4 ligases with ~70% overall sequence identity. Here, we show that the Smurf1 C2 domain interacts with the HECT domain and inhibits ligase activity in trans. However, in contrast to Smurf2, we find that full-length Smurf1 is a highly active Ub ligase, and we can attribute this striking difference in regulation to the lack of one WW domain (WW1) in Smurf1. Using NMR spectroscopy and biochemical assays, we identified the WW1 region as an additional inhibitory element in Smurf2 that cooperates with the C2 domain to enhance HECT domain binding and Smurf2 inhibition. Our work provides important insights into Smurf regulation and highlights that the activities of highly related proteins can be controlled in distinct ways.

Author Correction: The structure of the ubiquitin-like modifier FAT10 reveals an alternative targeting mechanism for proteasomal degradation

The original version of the Supplementary Information associated with this Article inadvertently omitted Supplementary Table 3. The HTML version of the Article has been updated to include a corrected version of the Supplementary Information.

The structure of the ubiquitin-like modifier FAT10 reveals an alternative targeting mechanism for proteasomal degradation

FAT10 is a ubiquitin-like modifier that directly targets proteins for proteasomal degradation. Here, we report the high-resolution structures of the two individual ubiquitin-like domains (UBD) of FAT10 that are joined by a flexible linker. While the UBDs of FAT10 show the typical ubiquitin-fold, their surfaces are entirely different from each other and from ubiquitin explaining their unique binding specificities. Deletion of the linker abrogates FAT10-conjugation while its mutation blocks auto-FAT10ylation of the FAT10-conjugating enzyme USE1 but not bulk conjugate formation. FAT10- but not ubiquitin-mediated degradation is independent of the segregase VCP/p97 in the presence but not the absence of FAT10’s unstructured N-terminal heptapeptide. Stabilization of the FAT10 UBDs strongly decelerates degradation suggesting that the intrinsic instability of FAT10 together with its disordered N-terminus enables the rapid, joint degradation of FAT10 and its substrates without the need for FAT10 de-conjugation and partial substrate unfolding.

The ubiquitin-like modifier FAT10 is composed of two ubiquitin-like domains (UBDs). Here the authors present the FAT10 UBD structures and show that the unstructured FAT10 N-terminal heptapeptide together with the poor stability of FAT10 facilitate the rapid proteasomal targeting of FAT10 along with its substrates.

In situ investigation of production processes in a large chamber scanning electron microscope

A large-chamber scanning electron microscope (LC-SEM) provides an ideal platform for the installation of large-scale in situ experiments. Our LC-SEM has internal chamber dimensions of 1,2 × 1,3 × 1,4 m³ (W × H × D) (Fig.1) and makes it possible to incorporate novel in situ experimental devices, which are reported on here. The present manuscript describes in detail the development of in situ test equipment for the study of a broad range of processes in production engineering. Direct observation of the materials modification mechanisms provides fundamental insight into the underlying process characteristics. An in situ turning device was developed, tested and used to observe the chip formation on the microstructure scale of a 43CrMo4-sample. Laser beam micro welding was integrated into the LC-SEM to achieve in situ analysis of the welding process on stainless steel 1.4310. A heating module was employed for in situ wetting experiments to observe the formation and solidification of the melt of a tin-copper brazing filler on an aluminium cast alloy.

β-Sheet Augmentation Is a Conserved Mechanism of Priming HECT E3 Ligases for Ubiquitin Ligation

Ubiquitin (Ub) ligases (E3s) catalyze the attachment of Ub chains to target proteins and thereby regulate a wide array of signal transduction pathways in eukaryotes. In HECT-type E3s, Ub first forms a thioester intermediate with a strictly conserved Cys in the C-lobe of the HECT domain and is then ligated via an isopeptide bond to a Lys residue in the substrate or a preceding Ub in a poly-Ub chain. To date, many key aspects of HECT-mediated Ub transfer have remained elusive. Here, we provide structural and functional insights into the catalytic mechanism of the HECT-type ligase Huwe1 and compare it to the unrelated, K63-specific Smurf2 E3, a member of the Nedd4 family. We found that the Huwe1 HECT domain, in contrast to Nedd4-family E3s, prioritizes K6- and K48-poly-Ub chains and does not interact with Ub in a non-covalent manner. Despite these mechanistic differences, we demonstrate that the architecture of the C-lobe~Ub intermediate is conserved between Huwe1 and Smurf2 and involves a reorientation of the very C-terminal residues. Moreover, in Nedd4 E3s and Huwe1, the individual sequence composition of the Huwe1 C-terminal tail modulates ubiquitination activity, without affecting thioester formation. In sum, our data suggest that catalysis of HECT ligases hold common features, such as the β-sheet augmentation that primes the enzymes for ligation, and variable elements, such as the sequence of the HECT C-terminal tail, that fine-tune ubiquitination activity and may aid in determining Ub chain specificity by positioning the substrate or acceptor Ub.

Structural basis for the interaction between the cell polarity proteins Par3 and Par6

Polarity is a fundamental property of most cell types. The Par protein complex is a major driving force in generating asymmetrically localized protein networks and consists of atypical protein kinase C (aPKC), Par3, and Par6. Dysfunction of this complex causes developmental abnormalities and diseases such as cancer. We identified a PDZ domain-binding motif in Par6 that was essential for its interaction with Par3 in vitro and for Par3-mediated membrane localization of Par6 in cultured cells. In fly embryos, we observed that the PDZ domain-binding motif was functionally redundant with the PDZ domain in targeting Par6 to the cortex of epithelial cells. Our structural analyses by x-ray crystallography and NMR spectroscopy showed that both the PDZ1 and PDZ3 domains but not the PDZ2 domain in Par3 engaged in a canonical interaction with the PDZ domain-binding motif in Par6. Par3 thus has the potential to recruit two Par6 proteins simultaneously, which may facilitate the assembly of polarity protein networks through multivalent PDZ domain interactions.

The adherens junction-associated LIM domain protein Smallish regulates epithelial morphogenesis

Cell–cell adhesion and cell shape are regulated at adherens junctions during embryonic morphogenesis. Beati et al. show that the Drosophila LIM domain protein Smallish interacts with Bazooka, Canoe, and Src42A at adherens junctions. Loss-of-function and gain-of-function phenotypes reveal a function for Smallish in regulation of actomyosin contractility and cell shape.

In epithelia, cells adhere to each other in a dynamic fashion, allowing the cells to change their shape and move along each other during morphogenesis. The regulation of adhesion occurs at the belt-shaped adherens junction, the zonula adherens (ZA). Formation of the ZA depends on components of the Par–atypical PKC (Par-aPKC) complex of polarity regulators. We have identified the Lin11, Isl-1, Mec-3 (LIM) protein Smallish (Smash), the orthologue of vertebrate LMO7, as a binding partner of Bazooka/Par-3 (Baz), a core component of the Par-aPKC complex. Smash also binds to Canoe/Afadin and the tyrosine kinase Src42A and localizes to the ZA in a planar polarized fashion. Animals lacking Smash show loss of planar cell polarity (PCP) in the embryonic epidermis and reduced cell bond tension, leading to severe defects during embryonic morphogenesis of epithelial tissues and organs. Overexpression of Smash causes apical constriction of epithelial cells. We propose that Smash is a key regulator of morphogenesis coordinating PCP and actomyosin contractility at the ZA.

Variations in truncal body circumferences affect fat mass quantification with bioimpedance analysis

OBJECTIVE

To test the hypothesis that variations in trunk circumferences influence the accuracy of bioimpedance analysis (BIA) for assessment of percent fat mass (%FM).

SUBJECTS AND METHODS

%FM was predicted with BIA, and compared with air-displacement plethysmography (ADP) in a small sample of 35 overweight (OW), 21 normal weight and 8 underweight volunteers. Waist and hip circumferences were assessed, and 15 of the OW subjects were measured before and after weight reduction.

RESULTS

BIA and ADP provided similar cross-sectional estimates of group mean %FM (28.9±10.0 and 31.3±13.0%, respectively). However, within individuals, there were large between-method differences (Diff(BIA-ADP)) ranging from -13 to +13 %FM. Furthermore, we found a systematic bias of BIA related to the degree of adiposity. Consequently, %FM and fat mass loss during weight reduction in OW were underestimated with BIA when compared with ADP. Waist and hip circumferences were inversely associated with resistance (R) and reactance (P<0.01), and with Diff(BIA-ADP) (P<0.001). In women, the variability in hip circumference explained 76%, and in men, the variability in waist circumference explained 59% of Diff(BIA-ADP).

CONCLUSION

Resistance changes associated with variations in trunk circumferences decrease resistance, and therefore impair the accuracy of BIA to assess %FM.

Neurohumoral and metabolic response to exercise in water

Atrial natriuretic peptide (ANP) stimulates lipid mobilization and lipid oxidation in humans. The mechanism appears to promote lipid mobilization during exercise. We tested the hypothesis that water immersion augments exercise-induced ANP release and that the change in ANP availability is associated with increased lipid mobilization and lipid oxidation. In an open randomized and cross-over fashion we studied 17 men (age 31+/-3.6 years; body mass index 24+/-1.7 kg/m(2); body fat 17+/-6.7%) on no medication. Subjects underwent two incremental exercise tests on a bicycle ergometer. One test was conducted on land and the other test during immersion in water up to the xiphoid process. In a subset (n=7), we obtained electromyography recordings in the left leg. We monitored gas exchange, blood pressure, and heart rate. In addition, we obtained blood samples towards the end of each exercise step to determine ANP, norepinephrine, epinephrine, lactate, free fatty acids, insulin, and glucose concentrations. Heart rate, systolic blood pressure, and oxygen consumption at the anaerobic threshold and during peak exercise were similar on land and with exercise in water. The respiratory quotient was mildly reduced when subjects exercised in water. Glucose and lactate measurements were decreased whereas free fatty acid concentrations were increased with exercise in water. Water immersion attenuated epinephrine and norepinephrine and augmented ANP release during exercise. Even though water immersion blunts exercise-induced sympathoadrenal activation, lipid mobilization and lipid oxidation rate are maintained or even improved. The response may be explained by augmented ANP release.

Determinants of exercise-induced fat oxidation in obese women and men

Endurance training at an intensity eliciting maximal fat oxidation may have a beneficial effect on body weight and glucose metabolism in obese patients. However, the exercise intensity at which maximal fat oxidation occurs and the factors limiting fat oxidation are not well studied in this population. Obese, otherwise healthy men (n=38) and women (n=91) performed an incremental exercise test up to exhaustion on a cycle ergometer. Substrate oxidation was estimated using indirect calorimetry. Magnetic resonance tomography and spectroscopy were conducted to assess body fat distribution and intramyocellular fat content. We determined the exercise intensity at which maximal body fat oxidation occurs and assessed whether body composition, body fat distribution, intramyocellular fat content, or oxidative capacity predict exercise-induced fat oxidation. Maximal exercise-induced fat oxidation was 0.30+/-0.02 g/min in men and 0.23+/-0.01 g/min in women (p<0.05). Exercise intensity at the maximum fat oxidation was 42+/-2.2% VO (2 max) in men and 43+/-1.7% VO (2 max) in women. With multivariate analysis, exercise-induced fat oxidation was related to fat-free mass, percent fat mass, and oxidative capacity, but not to absolute fat mass, visceral fat, or intramyocellular fat content. We conclude that in obese subjects the capacity to oxidize fat during exercise appears to be limited by skeletal muscle mass and oxidative capacity rather than the availability of visceral or intramyocellular fat.

The ubiquitin binding region of the Smurf HECT domain facilitates polyubiquitylation and binding of ubiquitylated substrates

Mono- and polyubiquitylation of proteins are key steps in a wide range of biological processes. However, the molecular mechanisms that mediate these different events are poorly understood. Here, we employed NMR spectroscopy to map a non-covalent ubiquitin binding surface (UBS) on the Smurf ubiquitin ligase HECT domain. Analysis of mutants of the HECT UBS reveal that interfering with the UBS surface blocked Smurf-dependent degradation of its substrate RhoA in cells. In vitro analysis revealed that the UBS was not required for UbcH7-dependent charging of the HECT catalytic cysteine. Surprisingly, although the UBS was required for polyubiquitylation of both Smurf itself and the Smurf substrate RhoA, it was not required for monoubiquitylation. Furthermore, we show that mutating the UBS interfered with efficient binding of a monoubiquitylated form of RhoA to the Smurf HECT domain. Our findings suggest the UBS promotes polyubiquitylation by stabilizing ubiquitylated substrate binding to the HECT domain.

Autoinhibition of the HECT-type ubiquitin ligase Smurf2 through its C2 domain

Ubiquitination of proteins is an abundant modification that controls numerous cellular processes. Many Ubiquitin (Ub) protein ligases (E3s) target both their substrates and themselves for degradation. However, the mechanisms regulating their catalytic activity are largely unknown. The C2-WW-HECT-domain E3 Smurf2 downregulates transforming growth factor-beta (TGF-beta) signaling by targeting itself, the adaptor protein Smad7, and TGF-beta receptor kinases for degradation. Here, we demonstrate that an intramolecular interaction between the C2 and HECT domains inhibits Smurf2 activity, stabilizes Smurf2 levels in cells, and similarly inhibits certain other C2-WW-HECT-domain E3s. Using NMR analysis the C2 domain was shown to bind in the vicinity of the catalytic cysteine, where it interferes with Ub thioester formation. The HECT-binding domain of Smad7, which activates Smurf2, antagonizes this inhibitory interaction. Thus, interactions between C2 and HECT domains autoinhibit a subset of HECT-type E3s to protect them and their substrates from futile degradation in cells.

An exchange-free measure of 15N transverse relaxation: an NMR spectroscopy application to the study of a folding intermediate with pervasive chemical exchange

A series of experiments are presented that provide an exchange-free measure of dipole-dipole (15)N transverse relaxation, R(dd), that can then be substituted for (15)N R(1rho) or R(2) rates in the study of internal protein dynamics. The method is predicated on the measurement of a series of relaxation rates involving (1)H-(15)N longitudinal order, anti-phase (1)H and (15)N single-quantum coherences, and (1)H-(15)N multiple quantum coherences; the relaxation rates of all coherences are measured under conditions of spin-locking. Results from detailed simulations and experiments on a number of protein systems establish that R(dd) values are independent of exchange and systematic errors from dipolar interactions with proximal protons are calculated to be less than 1-2%, on average, for applications to perdeuterated proteins. Simulations further indicate that the methodology is rather insensitive to the exact level of deuteration so long as proteins are reasonably highly deuterated (>50%). The utility of the methodology is demonstrated with applications involving protein L, ubiquitin, and a stabilized folding intermediate of apocytochrome b(562) that shows large contributions to (15)N R(1rho) relaxation from chemical exchange.

Fractional 13C enrichment of isolated carbons using [1-13C]- or [2- 13C]-glucose facilitates the accurate measurement of dynamics at backbone Calpha and side-chain methyl positions in proteins

A simple labeling approach is presented based on protein expression in [1-(13)C]- or [2-(13)C]-glucose containing media that produces molecules enriched at methyl carbon positions or backbone C(alpha) sites, respectively. All of the methyl groups, with the exception of Thr and Ile(delta1) are produced with isolated (13)C spins (i.e., no (13)C-(13)C one bond couplings), facilitating studies of dynamics through the use of spin-spin relaxation experiments without artifacts introduced by evolution due to large homonuclear scalar couplings. Carbon-alpha sites are labeled without concomitant labeling at C(beta) positions for 17 of the common 20 amino acids and there are no cases for which (13)C(alpha)-(13)CO spin pairs are observed. A large number of probes are thus available for the study of protein dynamics with the results obtained complimenting those from more traditional backbone (15)N studies. The utility of the labeling is established by recording (13)C R (1rho) and CPMG-based experiments on a number of different protein systems.

A change in conformational dynamics underlies the activation of Eph receptor tyrosine kinases

Eph receptor tyrosine kinases (RTKs) mediate numerous developmental processes. Their activity is regulated by auto-phosphorylation on two tyrosines within the juxtamembrane segment (JMS) immediately N-terminal to the kinase domain (KD). Here, we probe the molecular details of Eph kinase activation through mutational analysis, X-ray crystallography and NMR spectroscopy on auto-inhibited and active EphB2 and EphA4 fragments. We show that a Tyr750Ala gain-of-function mutation in the KD and JMS phosphorylation independently induce disorder of the JMS and its dissociation from the KD. Our X-ray analyses demonstrate that this occurs without major conformational changes to the KD and with only partial ordering of the KD activation segment. However, conformational exchange for helix alphaC in the N-terminal KD lobe and for the activation segment, coupled with increased inter-lobe dynamics, is observed upon kinase activation in our NMR analyses. Overall, our results suggest that a change in inter-lobe dynamics and the sampling of catalytically competent conformations for helix alphaC and the activation segment rather than a transition to a static active conformation underlies Eph RTK activation.

The structure of Prp40 FF1 domain and its interaction with the crn-TPR1 motif of Clf1 gives a new insight into the binding mode of FF domains

The yeast splicing factor Prp40 (pre-mRNA processing protein 40) consists of a pair of WW domains followed by several FF domains. The region comprising the FF domains has been shown to associate with the 5' end of U1 small nuclear RNA and to interact directly with two proteins, the Clf1 (Crooked neck-like factor 1) and the phosphorylated repeats of the C-terminal domain of RNA polymerase II (CTD-RNAPII). In this work we reported the solution structure of the first FF domain of Prp40 and the identification of a novel ligand-binding site in FF domains. By using chemical shift assays, we found a binding site for the N-terminal crooked neck tetratricopeptide repeat of Clf1 that is distinct and structurally separate from the previously identified CTD-RNAPII binding pocket of the FBP11 (formin-binding protein 11) FF1 domain. No interaction, however, was observed between the Prp40 FF1 domain and three different peptides derived from the CTD-RNAPII protein. Indeed, the equivalent CTD-RNAPII-binding site in the Prp40 FF1 domain is predominantly negatively charged and thus unfavorable for an interaction with phosphorylated peptide sequences. Sequence alignments and phylogenetic tree reconstructions using the FF domains of three functionally related proteins, Prp40, FBP11, and CA150, revealed that Prp40 and FBP11 are not orthologous proteins and supported the different ligand specificities shown by their respective FF1 domains. Our results also revealed that not all FF domains in Prp40 are functionally equivalent. We proposed that at least two different interaction surfaces exist in FF domains that have evolved to recognize distinct binding motifs.

Structural basis for the cytoskeletal association of Bcr-Abl/c-Abl

The Bcr-Abl tyrosine kinase causes different forms of leukemia in humans. Depending on its position within the cell, Bcr-Abl differentially affects cellular growth. However, no structural and molecular details for the anticipated localization determinants are available. We present the NMR structure of the F-actin binding domain (FABD) of Bcr-Abl and its cellular counterpart c-Abl. The FABD forms a compact left-handed four-helix bundle in solution. We show that the nuclear export signal (NES) previously reported in this region is part of the hydrophobic core and nonfunctional in the intact protein. In contrast, we could identify the critical residues of helix alphaIII that are responsible for F-actin binding and cytoskeletal association. We propose that these interactions represent a major determinant for both Bcr-Abl and c-Abl localization.

Integrin-actin interactions

The integrin family of extracellular matrix receptors regulates many aspects of cell life, in particular cell adhesion and migration. These two processes depend on organization of the actin cytoskeleton into adhesive and protrusive organelles in response to extracellular signals. Integrins are important switch points for the spatiotemporal control of actin-based motility in higher eukaryotes. Ligands of integrin cytoplasmic tails are central elements of signalling pathways involving small GTPases as well as protein and lipid kinases in the regulation of Factin crosslinking, actin treadmilling and de novo nucleation of actin filaments. We present an overview of common pathways and discuss recent evidence for their differential use by individual integrin receptors.

Solution structure and ligand recognition of the WW domain pair of the yeast splicing factor Prp40

The yeast splicing factor pre-mRNA processing protein 40 (Prp40) comprises two N-terminal WW domains, separated by a ten-residue linker, and six consecutive FF domains. In the spliceosome, the Prp40 WW domains participate in cross-intron bridging by interacting with proline-rich regions present in the branch-point binding protein (BBP) and the U5 small nuclear ribonucleoprotein component Prp8. Furthermore, binding of Prp40 to the phosphorylated C-terminal domain (CTD) of the largest subunit of RNA polymerase II is thought to link splicing to transcription. To gain insight into this complex interaction network we have determined the solution structure of the tandem Prp40 WW domains by NMR spectroscopy and performed chemical shift mapping experiments with different proline-rich peptides. The WW domains each adopt the characteristic triple-stranded beta-sheet structure and are connected by a stable alpha-helical linker. On the basis of a detailed analysis of residual dipolar couplings (RDC) and 15N relaxation data we show that the tandem Prp40 WW domains behave in solution as a single folded unit with unique alignment and diffusion tensor, respectively. Using [1H-15N]-RDCs, we were able to accurately define the relative orientation of the WW domains revealing that the binding pockets of each domain face opposite sides of the structure. Furthermore, we found that both Prp40 WW domains interact with PPxY motifs (where x is any residue) present in peptides derived from the splicing factors BBP and Prp8. Moreover, the Prp40 WW domains are shown to bind proline-rich peptides devoid of aromatic residues, which are also recognised by the Abl-SH3 domain and the WW domain of the mammalian Prp40 orthologue formin binding protein 11. In contrast, no interaction was observed between the Prp40 WW domains and the CTD repeats used in this work.

WW and SH3 domains, two different scaffolds to recognize proline-rich ligands

WW domains are small protein modules composed of approximately 40 amino acids. These domains fold as a stable, triple stranded beta-sheet and recognize proline-containing ligands. WW domains are found in many different signaling and structural proteins, often localized in the cytoplasm as well as in the cell nucleus. Based on analyses of seven structures of WW domains, we discuss their diverse binding preferences and sequence conservation patterns. While modeling WW domains for which structures have not been determined we uncovered a case of potential molecular and functional convergence between WW and SH3 domains. The binding surface of the modeled WW domain of Npw38 protein shows a remarkable similarity to the SH3 domain of Sem5 protein, confirming biochemical data on similar binding predilections of both domains.

Chemical development of latent fingerprints: 1,2-indanedione has come of age

The performance of 1,2-indanedione as a latent fingerprint reagent on some types of paper was found to exceed that of DFO, the leading fluorogenic fingerprint reagent. It even exceeds the performance of the sequence, DFO, followed by ninhydrin. No new prints could be observed when ninhydrin was applied after indanedione. On a large number of actual exhibits (used checks) indanedione developed 46% more identifiable prints than the sequence DFO-ninhydrin. A standard procedure for fingerprint development by indanedione is proposed. Best results are obtained with a 0.2% indanedione solution in HFE7100 solvent containing 7% ethyl acetate, but no acetic acid. It can be recommended to start using 1,2-indanedione, which is already commercially available, in actual fingerprint casework.

Indications for a novel muscular dystrophy pathway. gamma-filamin, the muscle-specific filamin isoform, interacts with myotilin

gamma-Filamin, also called ABP-L, is a filamin isoform that is specifically expressed in striated muscles, where it is predominantly localized in myofibrillar Z-discs. A minor fraction of the protein shows subsarcolemmal localization. Although gamma-filamin has the same overall structure as the two other known isoforms, it is the only isoform that carries a unique insertion in its immunoglobulin (Ig)-like domain 20. Sequencing of the genomic region encoding this part of the molecule shows that this insert is encoded by an extra exon. Transient transfections of the insert-bearing domain in skeletal muscle cells and cardiomyocytes show that this single domain is sufficient for targeting to developing and mature Z-discs. The yeast two-hybrid method was used to identify possible binding partners for the insert-bearing Ig-like domain 20 of gamma-filamin. The two Ig-like domains of the recently described alpha-actinin-binding Z-disc protein myotilin were found to interact directly with this filamin domain, indicating that the amino-terminal end of gamma-filamin may be indirectly anchored to alpha-actinin in the Z-disc via myotilin. Since defects in the myotilin gene were recently reported to cause a form of autosomal dominant limb-girdle muscular dystrophy, our findings provide a further contribution to the molecular understanding of this disease.

Reagents for the chemical development of latent fingerprints: scope and limitations of benzo[f]ninhydrin in comparison to ninhydrin

Benzo[f]ninhydrin was compared to ninhydrin for fingerprint development on paper. Overall, the performance of ninhydrin on exhibits was slightly better than that of benzo[f]ninhydrin. The significant advantages of the benzo[f]ninhydrin over ninhydrin were the much stronger fluorescence it gave after treatment with zinc salts and a slightly quicker reaction under ambient conditions. This fluorescence is, however, similar to that obtained with other reagents, such as DFO or ninhydrin analogs. These advantages apparently are not sufficient to justify regular usage of benzo[f]ninhydrin, especially when one considers its low solubility and high cost.

Water molecules in the binding cavity of intestinal fatty acid binding protein: dynamic characterization by water 17O and 2H magnetic relaxation dispersion

The hydration of intestinal fatty acid binding protein (IFABP) in apo-form and complexed with palmitate, oleate, and 1-anilino-8-naphthalene sulfonate (ANS) has been studied by water 17O and 2H magnetic relaxation dispersion (MRD) measurements. These ligands bind in a large internal cavity, displacing most of the crystallographically identified cavity water molecules. Unlike most other proteins, IFABP gives rise to MRD profiles with two dispersion steps. The low-frequency dispersion yields a correlation time of 7 ns at 300 K, matching the known tumbling time of IFABP. The dispersion amplitude requires only three (apo) or four (holo) long-lived and ordered water molecules (residence time 0.01-4 microseconds at 300 K). Comparison of MRD profiles from the different complexes indicates that the displaced cavity water molecules are short-lived. The few long-lived (>10 ns) water molecules required by the MRD data are tentatively assigned to crystallographic hydration sites on the basis of accessibility, positional order, and H-bonding. The amplitude of the high-frequency dispersion corresponds to 10-20 moderately ordered water molecules, with a correlation time of ca. 1 ns that may reflect a transient opening of the cavity required for exchange with external water.

Existence of the Frank-Starling mechanism in the failing human heart. Investigations on the organ, tissue, and sarcomere levels

BACKGROUND

The Frank-Starling mechanism is one of the most important physiological principles for regulation of contractile performance. We therefore studied the question of whether this mechanism may be absent or attenuated in end-stage failing human left ventricular myocardium.

METHODS AND RESULTS

Different methodological approaches were used to analyze the effects of this mechanism on the organ, tissue, and sarcomere levels: (1) In excised human whole left ventricles (2 donor hearts, 5 failing hearts), diastolic and systolic pressure-volume relationships were obtained. (2) In isolated muscle strip preparations from the left ventricular wall of donor hearts (n = 14) and failing hearts from patients with idiopathic dilated cardiomyopathy (n = 21) and ischemic cardiomyopathy (n = 11), peak developed force was measured at different muscle lengths of the preparation. (3) Skinned fiber preparations were obtained from failing right and left ventricles (n = 12). In all three studies, we clearly observed the existence of the Frank-Starling mechanism: (1) In isolated failing human left ventricles, peak developed isometric pressure is increased when the preload is elevated. (2) Peak developed tension is increased by approximately 50% to 70% (P < .01) in left ventricular preparations of failing and nonfailing ventricles when the muscles are stretched from 90% to 100% optimum length. (3) An increase in sarcomere length leads to a sensitization of contractile proteins of ventricular skinned fiber preparations from failing human hearts. At 1.9-microns sarcomere length, the EC50 value was 5.56 +/- 0.06, and at 2.3 microns it was 5.70 +/- 0.05 (P < .01; n = 7).

CONCLUSIONS

The Frank-Starling mechanism is maintained in end-stage failing human hearts, whereas significant alterations of diastolic myocardial distensibility are evident in chronic heart failure.

Brainstem auditory evoked potentials in migraine--evidence of increased side differences during the pain-free interval

Brainstem auditory evoked potentials (BAEPs) were recorded in 38 unselected patients (6 m./32 f.; age 18-54 yrs.) with various forms of migraine, during the pain-free interval. The values were compared to those of 50 control persons (18 m./32 f.; age 17-75 yrs.). Peak latencies (PL I-VI), interpeak latencies (IPL I-III, III-V, I-V) and side differences of all peaks (delta I-VI) were calculated. In contrast to PL's of migraine patients, all PL's of control persons were normally distributed. In 6 migraine patients (2 with basilar migraine) PL's were pathologically delayed. Statistical analysis did not show any significant difference in regard to PL's and IPL's between migraine patients and controls. However, side differences of all peaks (except peak IV,VI) were significantly increased in migraine patients as compared to controls. Our results indicate a slight but permanent impairment of brainstem function in migraine.

Double disability of hemiplegia and hip disarticulation: rehabilitation outcome

Double disability of hemiplegia and hip disarticulation is uncommon. To our knowledge, there are no reports of such patients and their rehabilitation outcomes. We report on a patient with hemiplegia and hip disarticulation who became independent in prosthetic ambulation and activities of daily living. Motivation, age, good neuromuscular status, and past successful prosthetic use favored the excellent rehabilitation outcome in this patient.

[Characterization of the effect of retransfusion of UV-irradiated autologous blood--synoptic examination of clinical, metabolic, rheologic and hemodynamic results in patients with arterial occlusive disease]

In 6 inpatients with angiographically ascertained arterial obstructive disease the influence of the retransfusion of uv-radiated own blood on metabolic, haemorheological, clinical and haemodynamic parameters was examined. In 4 patients a pseudoradiation was performed as control. The results confirm that under the ultra-violet radiation changes develop in the sense of a normalisation of the parameters examined. Here an improved walking capacity is accompanied by an improvement of the O2- and substrate utilisation of the tissue and the flowing properties. On the basis of the results the improvement of the microcirculation under ultra-violet radiation is to be derived. The sites of action of the ultra-violet radiation are shown in the causal chain in arterial obstructive diseases and partial steps of the mode of action are described.

[Experimental studies on the rheologic behavior of blood in ultraviolet therapy]

The increased apparent blood viscosity proved in peripheral circulatory disease, the frequent failure of therapy by means of vasodilating medicaments and the successful therapy with the help of ultraviolet radiation of blood (UVB) by means of various techniques motivated investigations of the flow properties of blood with UVB. In six patients with angiologically ascertained arterial occlusive disease the flow properties of blood were investigated under standardized conditions by both viscosimetric techniques and independent of it by means of the centrifugation method. Plasma viscosity, apparent blood viscosity, parameters of aggregation and deformation of erythrocytes were determined before and after fictitious UVB on the hand one and before and after real UVB on the other hand. It was shown that within the limit of measurement accuracy there were no significant differences between fictitious and real UVB in plasma viscosities. Both the aggregation parameter of the centrifugation method and the apparent blood viscosity for low shear gradients before the 3rd UVB and all following ones differed significantly from those of the first UVB. No changes were found in the deformation parameters HCC infinity and the apparent viscosity for high shear gradients during UVB therapy. Possible mechanisms leading to the demonstrated improvements of the flow properties of blood by means of UVB are discussed.