Crystal structure of the C-terminal half of tropomodulin and structural basis of actin filament pointed-end capping

Tropomodulin is the unique pointed-end capping protein of the actin-tropomyosin filament. By blocking elongation and depolymerization, tropomodulin regulates the architecture and the dynamics of the filament. Here we report the crystal structure at 1.45-A resolution of the C-terminal half of tropomodulin (C20), the actin-binding moiety of tropomodulin. C20 is a leucine-rich repeat domain, and this is the first actin-associated protein with a leucine-rich repeat. Binding assays suggested that C20 also interacts with the N-terminal fragment, M1-M2-M3, of nebulin. Based on the crystal structure, we propose a model for C20 docking to the actin subunit at the pointed end. Although speculative, the model is consistent with the idea that a tropomodulin molecule competes with an actin subunit for a pointed end. The model also suggests that interactions with tropomyosin, actin, and nebulin are all possible sources of influences on the dynamic properties of pointed-end capping by tropomodulin.

Therapeutic effects of glycine in isovaleric acidemia

The effect of glycine administration on acute leucine loading (125 mg/kg) was tested in a patient with isovaleric acidemia. Serum isovaleric acid at 1-3/4 hr after the leucine loading alone was elevated to 5.60 mg/100 ml and urinary isovaleryglycine excretion was 9.90 mg/mg creatine/24 hr. Whe the same amount of leucine was given with glycine (250 mg/kg) serum isovaleric acid was only 0.93 mg/200 ml. Unfortunately, urine was collected for only 12 hr after the leucine-glycine loading. However, the amount of urinary isovaleryglycine was 26.2 mg/mg creatine in this period. In the following experiments in which a meal containing 80 mg leucine/kg was given, serum isovaleric acid was elevated to 1.14 and 1.01 mg/100 ml at 3 hr and 6 hr after the loading, respectively. How-ever, serum isovaleric acid was only 0.53 and 0.79 mg/100 ml at 3 and 6 hr, respectively, when the identical mean was given with 2 g glycine. The effect of long term glycine administration (250 mg/kg/24 hr) was also tested. It did not prevent two ketotic episodes which were caused by infections. However, the duration of clinical symptoms such as vomiting and a large anion gap in the acute episodes were much shorter with rectal glycine administration. The patient's linear growth and weight gain durin glycine administration was much better than that in the pretreatment period.

Domain structure of tropomodulin: distinct properties of the N-terminal and C-terminal halves

The structure of tropomodulin, the unique capping protein for the pointed end (the slow-growing end) of an actin filament, was studied. An improved Escherichia coli expression system for chicken E-tropomodulin was established and tropomodulin was prepared, Tmod (N39), in which 15 amino acid residues from the original C-terminus are deleted at the DNA level. This expression and purification system accidentally co-produces an 11-kDa fragment with the original N-terminus (N11). By applying limited proteolysis to Tmod (N39), a 20-kDa C-terminal fragment (C20) was obtained. The limited proteolysis data, as well as the fluorescence spectrometry and CD analyses of Tmod (N39), C20 and N11, revealed that tropomodulin is an alpha-helical protein that consists of two distinct domains. The C-terminal half (20 kDa) is resistant to proteolysis, which suggests that this domain is tightly folded. In contrast, the N-terminal half is susceptible to proteolysis, indicating that in solution this half is likely to be extended or to form a highly flexible structure. Cross-linking experiments with glutaraldehyde indicated that Tmod (N39) and N11 can form complexes with tropomyosin, whereas C20 cannot. This confirms the previous report that the site(s) of interaction with tropomyosin resides in the N-terminal 11-kDa region of tropomodulin.

Acrodermatitis enteropathica without hypozincemia: therapeutic effect of a pancreatic enzyme preparation due to a zinc-binding ligand

The clinical course and intestinal absorption studies of a female infant who developed diarrhea after cessation of breast feeding, mood changes, and intermittently had mild perioral and perianal rashes are described. She showed a partial response to a pancreatic enzyme preparation which was attributed to its content of a zinc-binding ligand, picolinic acid. Complete recovery occurred on pharmacologic doses of zinc. Exacerbation occurred twice upon withdrawal of the oral zinc medication. The zinc concentrations of plasma and intestinal mucosa were normal.

High throughput crystallography of TB drug targets

Tuberculosis (TB) infects one-third of the world population. Despite 50 years of available drug treatments, TB continues to increase at a significant rate. The failure to control TB stems in part from the expense of delivering treatment to infected individuals and from complex treatment regimens. Incomplete treatment has fueled the emergence of multi-drug resistant (MDR) strains of Mycobacterium tuberculosis (Mtb). Reducing non-compliance by reducing the duration of chemotherapy will have a great impact on TB control. The development of new drugs that either kill persisting organisms, inhibit bacilli from entering the persistent phase, or convert the persistent bacilli into actively growing cells susceptible to our current drugs will have a positive effect. We are taking a multidisciplinary approach that will identify and characterize new drug targets that are essential for persistent Mtb. Targets are exposed to a battery of analyses including microarray experiments, bioinformatics, and genetic techniques to prioritize potential drug targets from Mtb for structural analysis. Our core structural genomics pipeline works with the individual laboratories to produce diffraction quality crystals of targeted proteins, and structural analysis will be completed by the individual laboratories. We also have capabilities for functional analysis and the virtual ligand screening to identify novel inhibitors for target validation. Our overarching goals are to increase the knowledge of Mtb pathogenesis using the TB research community to drive structural genomics, particularly related to persistence, develop a central repository for TB research reagents, and discover chemical inhibitors of drug targets for future development of lead compounds.

The TB Structural Genomics Consortium: a decade of progress

The TB Structural Genomics Consortium is a worldwide organization of collaborators whose mission is the comprehensive structural determination and analyses of Mycobacterium tuberculosis proteins to ultimately aid in tuberculosis diagnosis and treatment. Congruent to the overall vision, Consortium members have additionally established an integrated facilities core to streamline M. tuberculosis structural biology and developed bioinformatics resources for data mining. This review aims to share the latest Consortium developments with the TB community, including recent structures of proteins that play significant roles within M. tuberculosis. Atomic resolution details may unravel mechanistic insights and reveal unique and novel protein features, as well as important protein-protein and protein-ligand interactions, which ultimately lead to a better understanding of M. tuberculosis biology and may be exploited for rational, structure-based therapeutics design.

Gyrate atrophy of the choroid and retina. Early findings

Examination of two sisters ages 2 years 10 months and 6 years four months with gyrate atrophy of the choroid and retina provided an opportunity for detailed clinical investigation. Although the chorioretinal lesions were confined to the peripheral retina in the older case and were quite minimal in the younger case, there was electroretinographic evidence of marked involvement of the cone and rod systems. These cases offer an opportunity to assess an arginine restricted diet in preventing the progress of the disease.

Expanding the pleuromutilin class of antibiotics by de novo chemical synthesis

New pleuromutilin-like compounds were synthesized in approximately 11 steps from 3-allylcyclopent-2-enone by a strategy featuring sequential carbonyl addition reactions. Several analogs possessing the C14 tiamulin ester side chain displayed activity in a Mycobacterium tuberculosis mc(2)7000 assay. The results described herein provide a basis for further efforts to expand the structural and stereochemical diversity of the pleuromutilin class of bacterial protein synthesis inhibitors through advances in chemical synthesis.

Inhibition of bone marrow stem cell growth in vitro by methylmalonic acid: a mechanism for pancytopenia in a patient with methylmalonic acidemia

A 7-week-old infant with methylmalonic acidemia had pancytopenia and hypoplastic bone marrow. The patient responded to large doses of vitamin B12 treatment, and within 3 wk, the blood counts and bone marrow cellularity returned to normal. To understand the mechanism of marrow depression in this infant, we examined the effect of the patient's plasma and methylmalonic acid itself on the in vitro growth of bone marrow-committed stem cells. The patient's plasma obtained before B12 treatment completely inhibited the marrow cell growth, whereas the posttreatment plasma showed no inhibition. Methylmalonic acid when added to the culture dishes in concentrations comparable to those reported in plasma of methylmalonic acidemia patients, inhibited growth of marrow stem cells in a concentration-dependent fashion. On the other hand, 16 to 18 hr incubation of cells in the same concentration of methylmalonic acid did not affect the recovery of viability of the cells. The observations suggest that methylmalonic acid is inhibitory to the proliferation of marrow stem cells. The mechanism of inhibition is yet to be elucidated.

Food restriction as a form of child abuse in ten cases of psychosocial deprivation dwarfism

Ten children with a psychosocial deprivation syndrome had linear growth failure, retarded bone age, a voracious and bizarre appetite, and behavior abnormalities which were a consequence of maternal rejection. Direct and indirect evidence suggests that their food had been persistently restricted by mothers who abused the children physically and had personality traits characteristic of such mothers. Most of the children had a low IQ. Weight recovery occurred regularly in the hospital and in three cases in the home, providing food was not restricted. Diagnosis was difficult because ravenous appetites and abnormal stools suggested malabsorption in seven cases; however, histories, absorption tests, and weight recovery which occurred despite temporary persistence of abnormal stools indicated that malabsorption was not the primary cause of malnutrition. Deviant be havior and abnormal stools were used to rationalize frustration and food restriction. Intensive psychotherapy of the mother is necessary.

The association between the socioeconomic status and anxiety-depression comorbidity in patients with psoriasis: a nationwide population-based study

BACKGROUND

Numerous studies have indicated that comorbid anxiety and depression are associated with a more severe course of illness. Yet generally, the study of the effect of psoriasis on patients' mental health has considered anxiety and depression to be separate states.

OBJECTIVE

To measure the association between psoriasis and anxiety, depression and anxiety-depression co-occurrence among patients according to their socioeconomic statuses (SES).

METHODS

A nationwide population-based study of psoriasis patients and age and gender frequency-matched controls (n = 255 862) was designed. Diagnostic data were obtained from Clalit Health Services, the largest managed care organization in Israel. This database was established using continuous real-time input from healthcare providers, pharmacies, medical care facilities and administrative computerized operating systems.

RESULTS

After controlling for demographic and clinical variables, psoriasis was associated with anxiety (OR 1.11, 95% CI 1.01-1.23, P < 0.05), depression (OR 1.17, 95% CI 1.08-1.26, P < 0.001), and anxiety and depression co-occurrence (OR 1.32, 95% CI 1.21-1.45, P < 0.001) among patients with low SES, yet was associated only with anxiety (OR 1.15 95% CI 1.04-1.27, P < 0.001) but not depression or comorbid anxiety-depression among patients with high SES. Survival analyses indicated that between the ages of 40 and 60, the cumulative probability of psoriasis patients with low SES to suffer from anxiety, depression and their co-occurrence inclined more sharply with age as compared to psoriasis patients with high SES.

CONCLUSIONS

As psoriasis patients with low SES are prone to suffer from more severe courses of anxiety and depression, the choice of treatment of psoriasis should address the SES as well as the underlying psychiatric disease.

Atypical clinical course of ornithine transcarbamylase deficiency due to a new mutant (comparison with Reye's disease)

A male infant with ornithine transcarbamylase (OTC) deficiency is described who was relatively symptom free for 4 months, gradually developed severe spasticity due to cerebral atrophy, and died at 13 months of age. Liver OTC activity was 1.5% of the normal mean. The mutant OTC showed an increased apparent Km for ornithine and an increased pH optimum. These kinetic findings fail to explain the atypical clinical course. The clinical picture of patients with genetic OTC deficiency who present during acute exacerbations together with the elevation of serum glutamic oxaloacetic transaminase and microvesicular fat accumulation in liver, as seen in this case, may suggest Reye's syndrome; however, electronmicroscopic examination of this patient suggested that the normal appearance of mitochondria helps to distinguish the two.

Group interpersonal psychotherapy for patients with major depression disorder - pilot study

BACKGROUND

This study evaluated the effectiveness of group interpersonal psychotherapy (IPT-G) for patients suffering from moderate to severe major depressive disorder (MDD), and who responded to antidepressant drugs during the acute phase treatment.

METHODS

Subjects were allocated into two groups: in the study group subjects entered IPT-G while in the comparison group subjects continued with standard treatment. All subjects were assessed five times during and 6 months after the termination of the IPT-G in a double-blind, matched-control design.

RESULTS

Subjects who participated in the IPT-G demonstrated significant improvement of their depressive symptoms compared to those who received the standard treatment both during the group therapy and in a 6-month follow-up period.

CONCLUSIONS

Our preliminary results suggest that IPT in a group setting might be effective for a subset of patients who respond to antidepressant medication.

LIMITATIONS

Small group of patients, lack of different types of treatment as control groups.

Cerebrospinal fluid glycine in nonketotic hyperglycinemic: effect of treatment with sodium benzoate and a ventricular shunt

In three infants with nonketotic hyperglycinemia, glycine was increased three-to fourfold in plasma, 13- to 28-fold in lumbar spinal fluid, and was higher yet in ventricular fluid. Oral sodium benzoate lowered cerebrospinal fluid (CSF) glycine by greater than 40%, but did not change the abnormal plasma: CSF ratio. An adult control, made hyperglycinemic with oral glycine, had a normal plasma: CSF ratio. Treatment of one patient with sodium benzoate from birth did not prevent mental retardation; the degree of brain stem depression was a function of CSF glycine in another patient. The persistance of glycine elevation in CSF, although therapy maintained normal concentration in plasma, appears to be caused by overproduction in brain and limitation of the high-capacity lumbar spinal reabsorptive mechanism. Treatment through lowering of CNS glycine by use of a ventricular shunt was explored.

Relation of specific dynamic action of food (SDA) to growth in rats

The relation between food induced thermogenesis and anabolic processes was investigated in normal and malnourished rats. The metabolic rate was measured 5 and 17 hr after food removal. The difference between the two measurements was 3.9% during growth arrest of malnourished rats gaining 0.6 g/day, but 20.0 and 28.7% during growth recovery when rats were gaining 4.1 and 5.3 g/day, respectively. The 5 hr postprandial metabolic rates rose in normal rats from 15.6 kcal/day at 4 weeks to 45.3 kcal/day at 15 weeks, and then declined to 38.5 kcal/day at 36 weeks. The difference between 5 and 17 hr postprandial metabolic rates was 28.8% in 5 to 15-week-old rats gaining 5.2 g/day, and 1.1% in 24 to 32-week-old rats who were no longer gaining weight.

Binding Mechanism of the N-Terminal SH3 Domain of CrkII and Proline-Rich Motifs in cAbl

The N-terminal Src homology 3 (nSH3) domain of a signaling adaptor protein, CT-10 regulator of kinase II (CrkII), recognizes proline-rich motifs (PRMs) of binding partners, such as cAbl kinase. The interaction between CrkII and cAbl kinase is involved in the regulation of cell spreading, microbial pathogenesis, and cancer metastasis. Here, we report the detailed biophysical characterizations of the interactions between the nSH3 domain of CrkII and PRMs in cAbl. We identified that the nSH3 domain of CrkII binds to three PRMs in cAbl with virtually identical affinities. Structural studies, by using x-ray crystallography and NMR spectroscopy, revealed that the binding modes of all three nSH3:PRM complexes are highly similar to each other. Van 't Hoff analysis revealed that nSH3:PRM interaction is associated with favorable enthalpy and unfavorable entropy change. The combination of experimentally determined thermodynamic parameters, structure-based calculations, and (15)N NMR relaxation analysis highlights the energetic contribution of conformational entropy change upon the complex formation, and water molecules structured in the binding interface of the nSH3:PRM complex. Understanding the molecular basis of nSH3:PRM interaction will provide, to our knowledge, new insights for the rational design of small molecules targeting the interaction between CrkII and cAbl.

Tryptophan deficiency and picolinic acid: effect on zinc metabolism and clinical manifestations of pellagra

In five experiments, rats were fed tryptophan (Tryp)-deficient diets with 6-12 micrograms/g zinc (Zn) and, in one experiment, a Zn-deficient diet to test the effect on clinical manifestations, plasma and bone Zn, and ability of picolinic acid (PA) or extra (12 micrograms/g) Zn to compensate. Tryp deficiency caused classical manifestations of pellagra although niacin intake was in excess of normal requirements. At marginal Zn intakes, oral PA caused a significant increase of plasma Zn and, compared with Tryp-adequate controls, Tryp deficiency resulted in lower plasma Zn and plasma:bone Zn ratios. Extra Zn (total 24 micrograms/g) was ineffective. Subcutaneous PA showed a tendency to lower plasma Zn. PA had no effect on clinical manifestations. We conclude that a Tryp metabolite other than nicotinic acid is necessary in the prevention of pellagra. Our hypothesis links this finding with the observed Tryp and PA effect on Zn metabolism.

Picolinic acid in acrodermatitis enteropathica: evidence for a disorder of tryptophan metabolism

Three children with acrodermatitis enteropathica (AE) were treated with oral zinc dipicolinate (zinc-PA). The daily dose of zinc required to prevent exacerbations, when administered as the dipicolinate complex, was one-third the minimum amount of zinc required as the sulfate salt. The concentration of picolinic acid in the plasma of asymptomatic children with AE was significantly less than that of normal children. However, oral treatment with PA alone was ineffective. The plasma of the three AE children contained a measurable quantity of kynurenine which was undetectable in plasma from normal children. Absorption of an oral zinc load was normal. The results support the hypothesis that the genetic defect in AE is in the tryptophan pathway, although the role of PA in zinc metabolism remains to be defined.

Transient neonatal zinc deficiency

We report an infant who developed clinical manifestations of zinc deficiency during the first month of life although the diet was adequate for zinc and no other causes could be ascertained. The diagnosis was confirmed by low plasma-zinc concentrations and a positive response to zinc treatment. The fatty acid profile of plasma phospholipids was typical of zinc deficiency (ie, arachidonic acid was markedly decreased). The transient nature of this disorder was evident when no relapse occurred after cessation of zinc therapy and plasma-zinc and arachidonic acid concentrations remained normal. Several explanations for the development of transient neonatal zinc deficiency are offered. The observation demonstrates that occasional infants may have requirements for zinc that are beyond the intakes of the conventional RDA.