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PubMed2005

Drying and hydrophobic collapse of paraffin plates.

We perform molecular dynamics simulations of the hydrophobic collapse of two paraffin plates to examine how the collapse is mediated by realistic paraffin-water attractive van der Waals forces. We explore several aspects of the drying transition between the plates, including the critical separation for drying and the critical size of the vapor bubble required for the nucleation of the drying event. We also investigate the kinetics of hydrophobic collapse and find that the hydrophobic collapse occurs in about 100 ps. We compare these results with the simulations with the plate-water van der Waals attractions turned off and with recent results on the hydrophobic collapse of multidomain proteins. Last, we discuss the relationship among the dewetting transition critical distance, van der Waals potential well depth, and water contact angle on solute surface using a simple macroscopic theory.

Chemistry, Physical↗
PubMed2006

Atomistic simulations of langmuir monolayer collapse.

Monolayers at the vapor/water interface collapse by exploring the third dimension at sufficient lateral compression, either by forming three-dimensional structures or by solubilization into the aqueous solution. In this paper, we provide an atomistic description of collapse from molecular dynamics (MD) simulations. More specifically, we investigate monolayers of arachidic acids spread on pure water and in an aqueous solution with Ca2+ ions in the subphase. In both cases, it is found that the collapsed systems generally lead to the formation of multilayer structures, which in the system with Ca2+ ions, proceeds by an intermediate regime where the monolayer exhibits significant roughness (of the order of 4 A). If no roughness is present, the system forms collapsed structures into the aqueous solution. The computational cost of atomic MD limits our simulations to relatively small system sizes, fast compression rates, and temporal scales on the order of a nanosecond. We discuss the issues caused by these limitations and present a detailed discussion of how the collapse regime proceeds at long time scales. We conclude with a summary of the implications of our results for further theoretical and experimental studies.

Journal Article↗
PubMed2000

A collapsed non-native RNA folding state.

At physiological Mg2+ concentrations, the catalytic core of the bI5 group I intron does not fold into its native structure. In contrast, as judged by the global size, this RNA undergoes structural collapse at Mg 2+ concentrations much lower than required to drive folding of the RNA completely to the native state. The bI5 RNA therefore exists in equilibrium between expanded and collapsed non-native states. The activation energy of RNA folding from the collapsed state to the native state is negligible and the reaction is not accelerated by the addition of urea. This collapsed state is thus distinct from the kinetic traps observed during folding of other large RNAs. The collapsed non-native state forms readily in the case of bI5 RNA and may exist generically prior to assembly of other ribonucleoprotein holoenzymes, such as the ribosome.

Base Sequence↗
PubMed2001

A collapsed state functions to self-chaperone RNA folding into a native ribonucleoprotein complex.

Most large RNAs achieve their active, native structures only as complexes with one or more cofactor proteins. By varying the Mg(2+) concentration, the catalytic core of the bI5 group I intron RNA can be manipulated into one of three states, expanded, collapsed or native, or into balanced equilibria between these states. Under near-physiological conditions, the bI5 RNA folds rapidly to a collapsed but non-native state. Hydroxyl radical footprinting demonstrates that assembly with the CBP2 protein cofactor chases the RNA from the collapsed state to the native state. In contrast, CBP2 also binds to the RNA in the expanded state to form many non-native interactions. This structural picture is reinforced by functional splicing experiments showing that RNA in an expanded state forms a non-productive, kinetically trapped complex with CBP2. Thus, rapid folding to the collapsed state functions to self-chaperone bI5 RNA folding by preventing premature interaction with its protein cofactor. This productive, self-chaperoning role for RNA collapsed states may be especially important to avert misassembly of large multi-component RNA-protein machines in the cell.

Animals↗
PubMed2001

Phosphorylation of cofilin by LIM-kinase is necessary for semaphorin 3A-induced growth cone collapse.

Semaphorin 3A is a chemorepulsive axonal guidance molecule that depolymerizes the actin cytoskeleton and collapses growth cones of dorsal root ganglia neurons. Here we investigate the role of LIM-kinase 1, which phosphorylates an actin-depolymerizing protein, cofilin, in semaphorin 3A-induced growth cone collapse. Semaphorin 3A induced phosphorylation and dephosphorylation of cofilin at growth cones sequentially. A synthetic cell-permeable peptide containing a cofilin phosphorylation site inhibited LIM-kinase in vitro and in vivo, and essentially suppressed semaphorin 3A-induced growth cone collapse. A dominant-negative LIM kinase, which could not be activated by PAK or ROCK, suppressed the collapsing activity of semaphorin 3A. Phosphorylation of cofilin by LIM-kinase may be a critical signaling event in growth cone collapse by semaphorin 3A.

Actin Depolymerizing Factors↗
PubMed1996

Idiopathic collapsing focal segmental glomerulosclerosis: a clinicopathologic study.

A review of all native kidney biopsies at our center from 1974 to 1993 identified 43 cases of idiopathic focal segmental glomerulosclerosis (FSGS) with predominantly collapsing features and lacking evidence of HIV-1 infection or intravenous drug use. No case was identified before 1979 and the incidence of this entity has progressively increased over the past two decades. Compared to 50 age-matched controls of idiopathic FSGS with typical perihilar scars, the group of idiopathic collapsing FSGS displayed black racial predominance, a higher serum creatinine and more severe features of nephrotic syndrome at biopsy. Morphologic features of visceral epithelial cell hypertrophy and hyperplasia, tubular microcysts, tubular epithelial degenerative and regenerative features and interstitial edema were more prevalent and severe in collapsing FSGS. Median time to ESRD was rapid in collapsing FSGS versus controls (13.0 months vs. 62.5 months, P < 0.05). Correlates of progression to ESRD included a higher initial serum creatinine and failure to undergo remission of proteinuria. Both glomerulosclerosis and certain features of tubular damage were independent predictors of the level of renal function at time of biopsy, but not of the rate of progression of renal insufficiency. Although three patients had partial or complete spontaneous remissions, none of 26 patients treated with steroids alone responded. Idiopathic collapsing FSGS is a variant of FSGS with increasing incidence, distinct clinicopathologic features, black racial predominance, a rapidly progressive course and relative steroid resistance.

Adolescent↗
PubMed2005

Observation of a dewetting transition in the collapse of the melittin tetramer.

Marked hydration changes occur during the self-assembly of the melittin protein tetramer in water. Hydrophobicity induces a drying transition in the gap between simple sufficiently large (more than 1 nm(2)) strongly hydrophobic surfaces as they approach each other, resulting in the subsequent collapse of the system, as well as a depletion of water next to single surfaces. Here we investigate whether the hydrophobic induced collapse of multidomain proteins or the formation of protein oligimers exhibits a similar drying transition. We performed computer simulations to study the collapse of the tetramer of melittin in water, and observed a marked water drying transition inside a nanoscale channel of the tetramer (with a channel size of up to two or three water-molecule diameters). This transition, although occurring on a microscopic length scale, is analogous to a first-order phase transition from liquid to vapour. We find that this drying is very sensitive to single mutations of the three isoleucines to less hydrophobic residues and that such mutations in the right locations can switch the channel from being dry to being wet. Thus, quite subtle changes in hydrophobic surface topology can profoundly influence the drying transition. We show that, even in the presence of the polar protein backbone, sufficiently hydrophobic protein surfaces can induce a liquid-vapour transition providing an enormous driving force towards further collapse. This behaviour was unexpected because of the absence of drying in the collapse of the multidomain protein 2,3-dihydroxybiphenyl dioxygenase (BphC).

Dioxygenases↗
PubMed1999

Collapsing glomerulopathy in HIV and non-HIV patients: a clinicopathological and follow-up study.

UNLABELLED: Collapsing glomerulopathy in HIV and non-HIV patients: A clinicopathological and follow-up study. BACKGROUND: Collapsing glomerulopathy (CG) is a pattern of renal injury that is seen in association with HIV infection and that is increasingly recognized in non-HIV patients. METHODS: A review of native kidney biopsies with CG that were diagnosed between 1979 and 1997 in 18 HIV and 42 non-HIV patients is provided. RESULTS: HIV and non-HIV patients with CG were similar in terms of age, sex ratio, serum creatinine, proteinuria, the extent of collapsing and sclerosing glomerular lesions, and interstitial damage. A slight female predominance was found in both groups. In contrast to non-HIV patients, the HIV group was characterized by a high prevalence of blacks (94 vs. 57%), frequent tubuloreticular inclusions (76 vs. 29%), and microcystic tubular changes (72 vs. 40%). In 13 non-HIV patients, CG was associated with a systemic lupus erythematosus (SLE)-like disease (5), hepatitis C virus (HCV) infection (3), HTLV-I infection, MCTD, acute monoblastic leukemia, multiple myeloma, and cerebral arteritis. Overall, the renal survival of human immunodeficiency virus (HIV) and non-HIV patients with CG was not significantly different. Cox regression revealed that HIV infection had an adverse effect on short-term renal survival, with other significant risk factors being extensive interstitial fibrosis, high serum creatinine, proteinuria, and a low percentage of glomeruli with collapse. The slope of reciprocal creatinine was best predicted by the degree of proteinuria. Serum creatinine correlated with the extent of interstitial fibrosis, the male gender, and the percentage of glomeruli with collapse. Proteinuria was best predicted by the extent of effacement of podocyte foot processes. CONCLUSIONS: CG shares many clinicopathological similarities in HIV and non-HIV patients. In some non-HIV patients, CG was associated with autoimmune diseases, lymphoproliferative disorders, and viral infections.

Adult↗
PubMed2004

Collapsing glomerulopathy in adult still's disease.

Idiopathic collapsing glomerulopathy is a clinically and pathologically distinct variant of focal segmental glomerulosclerosis characterized clinically by a male and Afro-Caribbean racial predominance, proteinuria (often nephrotic range), and rapid progression to end-stage renal failure. Pathologically, the typical changes are global glomerular collapse leading to obliteration of glomerular capillary lumina, hypertrophy and hyperplasia of podocytes, and severe tubulointerstitial changes. A secondary form with almost identical pathologic features is described in association with human immunodeficiency virus infection. We describe a female patient who presented with multisystemic manifestations, including high spiking fever, arthralgias, lymphadenopathy, striking hyperferritinemia, and impaired renal function with proteinuria. Renal biopsy showed classic collapsing glomerulopathy. A diagnosis of adult Still's disease was made on the basis of Yamaguchi's criteria. The patient was treated with steroids, resulting in remission of the rheumatological condition closely paralleled by remission of proteinuria and renal function, thereby strongly suggesting a causative link between adult Still's disease and collapsing glomerulopathy in this patient. We propose that collapsing glomerulopathy ought to be considered in adult Still's disease with unexplained renal insufficiency or proteinuria.

Biopsy↗
PubMed2004

Advances in MR imaging of vertebral collapse.

Vertebral collapse is a frequently encountered entity in clinical practice. While diagnosing acute, benign traumatic types is usually not complicated, difficulties arise in determining the etiology of vertebral collapse when there is no history of significant trauma, especially in older populations. Considering up to one-third of vertebral collapse in patients with a known primary malignancy are benign, the diagnosis becomes even more difficult when there is a history of malignancy. Additionally, because primary cancer patients may be immunocompromised, the possibility of infectious vertebral collapse should also be entertained. The purpose of this article is to review all recent magnetic resonance imaging aspects of differentiating osteoporotic, malignant, and infectious vertebral collapse.

Diagnosis, Differential↗
PubMed2006

Mapping protein collapse with single-molecule fluorescence and kinetic synchrotron radiation circular dichroism spectroscopy.

We have used the combination of single-molecule Förster resonance energy transfer and kinetic synchrotron radiation circular dichroism experiments to probe the conformational ensemble of the collapsed unfolded state of the small cold shock protein CspTm under near-native conditions. This regime is physiologically most relevant but difficult to access experimentally, because the equilibrium signal in ensemble experiments is dominated by folded molecules. Here, we avoid this problem in two ways. One is the use of single-molecule Förster resonance energy transfer, which allows the separation of folded and unfolded subpopulations at equilibrium and provides information on long-range intramolecular distance distributions. From experiments with donor and acceptor chromophores placed at different positions within the chain, we find that the distance distributions in unfolded CspTm agree surprisingly well with a Gaussian chain not only at high concentrations of denaturant, where the polypeptide chain is expanded, but also at low denaturant concentrations, where the chain is collapsed. The second, complementary approach is synchrotron radiation circular dichroism spectroscopy of collapsed unfolded molecules transiently populated with a microfluidic device that enables rapid mixing. The results indicate a beta-structure content of the collapsed unfolded state of approximately 20% compared with the folded protein. This suggests that collapse can induce secondary structure in an unfolded state without interfering with long-range distance distributions characteristic of a random coil, which were previously found only for highly expanded unfolded proteins.

Circular Dichroism↗
PubMed1956

Reversible collapse of rabbit ears after intravenous papain, and prevention of recovery by cortisone.

A substance has been demonstrated in solutions of crude papain, which, when injected intravenously into 1 kilo rabbits, in amounts less than 5 mg., results in complete collapse of both ears. The phenomenon becomes visible 4 hours after injection, and is complete within 24 hours. 3 or 4 days after papain, the ears gradually reassume their normal form. Ear collapse is associated with depletion of the ear cartilage matrix, and the disappearance of basophilia from the matrix. Similar changes occur in all other cartilage tissues, including bones, joints, larynx, trachea, and bronchi. At the time when the ears are restored to normal shape, the basophilic matrix reappears in cartilage. Repeated injections of papain, over a period of 2 or 3 weeks, bring about immunity to the phenomenon of ear collapse. When the arterial circulation to one ear is occluded for 15 minutes at the time of injection of papain, this ear is protected against collapse. The effect of crude papain could not be reproduced by crystalline papain protease or crystalline papain lysozyme, which together comprise a considerable portion of the dry weight of papain. The nature of the responsible factor has not been determined, and the possibility that chymopapain may be implicated is currently under study. Cortisone prevents the return of papain-collapsed ears to their normal shape and rigidity. Possibly this reflects a capacity of cortisone to impede the synthesis or deposition of sulfated mucopolysaccharides in tissues.

Animals↗
PubMed1985

Pulmonary lobe blood flow during ventilation hypoxia and lobar collapse in the dog.

The aim of the present study was to determine whether the diversion of blood flow away from a collapsed pulmonary lobe is due to hypoxic pulmonary vasoconstriction alone, or whether hypercapnia and mechanical factors also contribute. Hypoxic pulmonary vasoconstriction was tested in a canine pulmonary left lower lobe. Alveolar hypoxia was produced by absorption collapse or by ventilation with 7% oxygen, which has previously been shown to produce an end-pulmonary capillary pO2 similar to mixed venous pO2. The proportion of the cardiac output flowing to the lobe was reduced in both hypoxic states but was significantly lower during collapse than during ventilation hypoxia. The beta 1-adrenergic agonist dobutamine hydrochloride (30 micrograms X kg-1 X min-1 iv) produced a significant increase in the proportion of the cardiac output flowing to the lobe during collapse but no significant change during ventilation hypoxia. It is concluded that changes in local pCO2 during collapse may account for the greater diversion of blood flow from the lobe when compared with ventilation hypoxia.

Animals↗
PubMed2003

The influence of lung volume on pharyngeal mechanics, collapsibility, and genioglossus muscle activation during sleep.

STUDY OBJECTIVES: Previous studies in both awake and sleeping humans have demonstrated that lung-volume changes substantially affect upper-airway size and pharyngeal resistance and, thus, may influence pharyngeal patency. We sought to systematically investigate the isolated effects of lung-volume changes on pharyngeal collapsibility and mechanics and genioglossus muscle activation during stable non-rapid eye movement sleep. We hypothesized that lower lung volumes would lead to increased pharyngeal collapsibility, airflow resistance, and, in compensation, augmented genioglossus muscle activation. DESIGN: Nineteen normal individuals (age, 30.4 +/- 0.5 years; body mass index: 24.5 +/- 0.4 kg/m2) were studied during stable non-rapid eye movement sleep in a rigid head-out shell equipped with a variable positive/negative pressure attachment for manipulations of extrathoracic pressure and, thus, lung volume. SETTING: Sleep physiology laboratory. PARTICIPANTS: Normal healthy volunteers. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: We measured change in end-expiratory lung volume (EELV) (magnetometers), genioglossus electromyogram (GGEMG) (intramuscular electrodes), pharyngeal pressure, and collapsibility of the pharynx in response to a brief pulse of negative pressure (-8 to -15 cm H2O) under the following conditions: (1) baseline, (2) increased EELV (+1 liter), and (3) decreased EELV (-0.6 liter). Reduced lung volumes led to increased inspiratory airflow resistance (7.54 +/- 2.80 cm H2O x L(-1) x s(-1) vs 4.53 +/- 1.05 cm H2O x L(-1) x s(-1), mean +/- SEM, P = 0.02) and increased genioglossus muscle activation (GGEMG peak 14.6% +/- 1.5% of maximum vs 8.6% +/- 1.5% of maximum, maximum P = 0.001) compared to baseline. The pharynx was also more collapsible at low lung volumes (4.3 +/- 0.5 cm H2O vs 5.4 +/- 0.6 cm H2O, P = 0.04). CONCLUSIONS: We conclude that upper-airway muscles respond to changes in lung volumes but not adequately to prevent increased collapsibility. These results suggest that lung volume has an important influence on pharyngeal patency during non-rapid eye movement sleep in normal individuals.

Adult↗
PubMed2002

Growth cone collapsing effect of lidocaine on DRG neurons is partially reversed by several neurotrophic factors.

BACKGROUND: Local anesthetics were suggested to have a potential for neurotoxicity in both clinical reports and laboratory experiments. Growing neurons have been shown to be susceptible to the toxic effects of local anesthetics in culture. These findings have generated the interest in factors that would rescue the neurons affected by the neurotoxicity of local anesthetics. METHODS: Primary cultured dorsal root ganglia were isolated from age-matched chick embryos and exposed to lidocaine. After 60 min of exposure, the culture media were replaced to wash out the lidocaine. Neurotrophic factors (NTFs)-brain-derived neurotrophic factor, glial-derived neurotrophic factor, or neurotrophin 3-were added to the replacement media to examine the capacity of these NTFs to support the reversibility of the lidocaine-induced growth cone collapse. The growth cone collapse assay was applied a quantitative method of assessment. RESULTS: When any of the three NTFs was added to the replacement media at a minimum concentration of 10 ng/ml, significantly high reversibility of the lidocaine-induced growth cone collapse was observed, especially at 48 h after washout (P < 0.05). At that time point, there was no significant difference between the values of growth cone collapse percentage in the cells that were exposed to lidocaine and supported by the NTFs after the washout, and the control cells (not exposed to lidocaine) (P > 0.05). CONCLUSION: The NTFs-brain-derived neurotrophic factor, glial-derived neurotrophic factor, and neurotrophin 3-were demonstrated to support the reversibility of lidocaine-induced growth cone collapse in primary cultured sensory neurons, an effect that was concentration- and time-dependent. Because similar effects were observed after tetracaine washout, the supporting effects of NTFs may not be specific to lidocaine.

Anesthetics, Local↗
PubMedDate not supplied

Acute lobar collapse in canine lungs.

A series of experiments was carried out on 28 dogs in which the following aspects were investigated: in 9 dogs, the special configuration of acute lobar atelectasis; in 10 dogs, the pressure-volume characteristics of collapsed and non-collapsed diaphragmatic lobes; in 12 dogs, the wet-weight/dry-weight ratios of atelectatic contralateral lobes; in 6 dogs, the amount of blood sequestered in atelectatic diaphragmatic lobes was estimated. The relationships of an atelectic lobe closely resemble those described in man. Loss of apposition between visceral and parietal pleural surfaces was never observed. The W/D weight ratio of the collapsed lobe invariably was higher than that of the non-collapsed contralateral lobe indicating a slight increase in the volume of fluid in the atelectatic lobe. No pressure-volume differences were found between atelectatic and non-collapsed lobes.

Acute Disease↗
PubMed1985

CT of obstructive lobar collapse.

The varied computed tomographic (CT) appearance of obstructive lobar collapse is described in 25 cases. CT is helpful in understanding the morphology and mechanisms of lobar collapse and in diagnosing atypical cases. The final shape of the collapsed lobe is dependent on the size and location of the obstructing tumor and on the amount of retained lung fluid. Focal bulging of the fissure (S-sign) is the most helpful sign in identifying the obstructing tumor. Differential enhancement could not separate the tumor from collapsed lung in six of eight (75%) of the cases studied with intravenous contrast, a finding at variance with previous reports. The limitations of CT in evaluating mediastinal or pleural invasion in the presence of lobar collapse are discussed.

Adult↗
PubMedDate not supplied

Computed tomography of combined right upper and middle lobe collapse.

We report two patients with combined right upper and middle lobe collapse and present the CT findings. The CT appearance is different from isolated right upper or middle lobe collapse, but similar to left upper lobe collapse. As with other types of lobar collapse, the diagnosis can usually be made from frontal and lateral chest radiography. However, occasionally the exact type of lung collapse may be unclear prior to CT, and thus CT may be useful in making the correct diagnosis.

Aged↗