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PubMed2006

The influence of macromolecular crowding on HIV-1 protease internal dynamics.

High macromolecular concentrations, or crowded conditions, have been shown to affect a wide variety of molecular processes, including diffusion, association and dissociation, and protein folding and stability. Here, we model the effect of macromolecular crowding on the internal dynamics of a protein, HIV-1 protease, using Brownian dynamics simulations. HIV-1 protease possesses a pair of flaps which are postulated to open in the early stages of its catalytic mechanism. Compared to low concentrations, close-packed concentrations of repulsive crowding agents are found to significantly reduce the fraction of time that the protease flaps are open. Macromolecular crowding is likely to have a major effect on in vivo enzyme activity, and may play an important regulatory role in the viral life cycle.

Amino Acids↗

PubMed2006

Processive movement of single kinesins on crowded microtubules visualized using quantum dots.

Kinesin-1 is a processive molecular motor transporting cargo along microtubules. Inside cells, several motors and microtubule-associated proteins compete for binding to microtubules. Therefore, the question arises how processive movement of kinesin-1 is affected by crowding on the microtubule. Here we use total internal reflection fluorescence microscopy to image in vitro the runs of single quantum dot-labelled kinesins on crowded microtubules under steady-state conditions and to measure the degree of crowding on a microtubule at steady-state. We find that the runs of kinesins are little affected by high kinesin densities on a microtubule. However, the presence of high densities of a mutant kinesin that is not able to step efficiently reduces the average speed of wild-type kinesin, while hardly changing its processivity. This indicates that kinesin waits in a strongly bound state on the microtubule when encountering an obstacle until the obstacle unbinds and frees the binding site for kinesin's next step. A simple kinetic model can explain quantitatively the behaviour of kinesin under both crowding conditions.

Biological Transport↗

PubMed2000

Triangular-shaped incisor crowns and crowding.

The purpose of this study was to establish if there is a correlation between the shape of the labial crowns of the incisors and crowding. Plaster cast models of 69 untreated individuals (30 males and 39 females) were evaluated. The casts were selected randomly from the collection at Seoul National University and Ajou University. With the use of Little's irregularity index, the sample was divided into 2 groups, a crowded group and a normal group. Repeated measurements of the maximum mesiodistal width of the incisal and cervical areas of the incisors were taken by means of a digital vernier caliper and a ratio of these measurements was calculated. The mean value for the crowded group was significantly larger in the incisal area (P <.01) and smaller in the cervical areas (P <.01) than corresponding values in the normal group. These ratios were correlated with the irregularity index (Pearson r(2) from 55% to 65%). The value obtained from the incisor width ratio in the normal group can be useful for the diagnosis and treatment of crowded malocclusion.

Case-Control Studies↗

PubMed2003

Incisor crown shape and crowding.

The aim of this study was to investigate correlations between the shape of mandibular incisor crowns and crowding. Study models of 50 untreated white subjects (25 men and 25 women) with varying degrees of crowding were studied. The lower incisors were sectioned and imaged at the contact point and midpoint levels, and the mesiodistal width was measured. Crowding was quantified by using both Little's irregularity index and anterior tooth size-arch length discrepancy. The ratio of the 2 mesiodistal widths was correlated with Little's irregularity index and anterior tooth size-arch length discrepancy. In the women, the ratio showed correlations of 0.52 (P =.008) and 0.55 (P =.005) for central and lateral incisors, respectively, with anterior tooth size-arch length discrepancy. No predictors of lower incisor crowding could be established from mandibular incisor crown shape in this study.

Adolescent↗

PubMed2003

Atomic-level observation of macromolecular crowding effects: escape of a protein from the GroEL cage.

Experimental work has demonstrated that the efficient operation of the GroEL-GroES chaperonin machinery is sensitive to the presence of macromolecular crowding agents. Here, I describe atomically detailed computer simulations that provide a microscopic view of how crowding effects are exerted. Simulations were performed to compute the free energy required to extract the protein rhodanese from the central cavity of GroEL into solutions containing a range of crowder concentrations. The computed energetics allow the total yield of folded protein to be predicted; the calculated yields show a nonlinear dependence on the concentration of crowding agent identical to that observed experimentally. The close correspondence between simulation and experiment prompts the use of the former in a truly predictive setting: simulations are used to suggest that more effective crowding agents might be designed by exploiting an "agoraphobic effect."

Adenosine Triphosphate↗

PubMed2003

Essential cell division protein FtsZ assembles into one monomer-thick ribbons under conditions resembling the crowded intracellular environment.

Experimental conditions that simulate the crowded bacterial cytoplasmic environment have been used to study the assembly of the essential cell division protein FtsZ from Escherichia coli. In solutions containing a suitable concentration of physiological osmolytes, macromolecular crowding promotes the GTP-dependent assembly of FtsZ into dynamic two-dimensional polymers that disassemble upon GTP depletion. Atomic force microscopy reveals that these FtsZ polymers adopt the shape of ribbons that are one subunit thick. When compared with the FtsZ filaments observed in vitro in the absence of crowding, the ribbons show a lag in the GTPase activity and a decrease in the GTPase rate and in the rate of GTP exchange within the polymer. We propose that, in the crowded bacterial cytoplasm under assembly-promoting conditions, the FtsZ filaments tend to align forming dynamic ribbon polymers. In vivo these ribbons would fit into the Z-ring even in the absence of other interactions. Therefore, the presence of mechanisms to prevent the spontaneous assembly of the Z-ring in non-dividing cells must be invoked.

Bacterial Proteins↗

PubMed1996

Late lower arch crowding in relation to the direction of eruption.

The change in lower arch crowding 3-4 years after second permanent molar eruption was examined in 85 subjects, in relation to the angulation and change in angulation of molars and incisors relative to the mandibular plane using correlation and multiple regression analyses. Crowding increased significantly during the observation periods. Changes in molar and incisor angulation in both mesial and distal directions were observed. The increase in crowding was not related to molar or incisor angulation at 12 years. Some association between increase in crowding, reduction in arch depth and retroclination of incisors was found.

Adolescent↗

PubMed2005

Third molar influence on dental arch crowding.

The aim of the present study was to measure the dental arches in order to assess the potential influence of third molars on lower incisor crowding. Changes in dental arch dimensions were assessed in 47 patients (36 females, 11 males) three years following either removal of the third molars or deciding to leave them in situ. A dental pantomogram (DPT) was taken at the start of the study and plaster study models were obtained at both the beginning and end of the observation period. The study models were used to measure crowding, and to prepare photocopies for linear measurements of the dental arch (length and width). Using the DPT, the ratio of retromolar space to the width of the crown of the third molar was calculated using the method originally described by Olive and Basford and later modified by Ganss (Ganss ratio). The results showed that the measurements of crowding and arch length and width had changed in 12 lower and two upper dental arches. The relationship between these results and the Ganss ratio was statistically significant. Calculation of the Ganss ratio may therefore assist investigations into the development of dental arch crowding and also help determine the indications for third molar removal.

Adolescent↗

PubMedDate not supplied

Adolescent peer crowd affiliation: linkages with health-risk behaviors and close friendships.

OBJECTIVE: To examine adolescents' peer crowd affiliation and its linkages with health-risk behaviors, their friends' health-risk behaviors, the presence of close friends in the same peer crowd, and adolescents' social acceptance. METHODS: We interviewed 250 high school students and identified six categories: popular, jocks, brains, burnouts, nonconformists, or average/other. Adolescents also reported on their health-risk behaviors (including use of cigarettes, alcohol, marijuana and other drugs; risky sexual behaviors; and other risk-taking behaviors), the health-risk behaviors of their friends, the peer crowd affiliation of their closest friends, and their perceived social acceptance. RESULTS: Burnouts and nonconformists had the highest levels of health-risk behaviors across the areas assessed, the greatest proportions of close friends who engaged in similar behaviors, and relatively low social acceptance from peers. Brains and their friends engaged in extremely low levels of health-risk behaviors. Jocks and populars also showed evidence of selected areas of health risk; these teens also were more socially accepted than others. In general, adolescents' closest friends were highly nested within the same peer crowds. CONCLUSIONS: The findings further our understanding of adolescent behaviors that put them at risk for serious adult onset conditions associated with high rates of morbidity and mortality. We discuss the implications of the findings for developing health promotion efforts for adolescents.

Adolescent↗

PubMed2006

Adolescents' eating, exercise, and weight control behaviors: does peer crowd affiliation play a role?

OBJECTIVE: To examine the association between peer crowd affiliation (e.g., Jocks, Populars, Burnouts, Brains) and adolescents' eating, exercise, and weight control behaviors. The roles of gender and ethnicity were also examined. METHOD: Ethnically diverse adolescents (N = 705; 66% girls) completed the Peer Crowd Questionnaire, eating and exercise items from the Youth Risk Behavior Surveillance System, and weight control behaviors from the Eating Attitudes Test-12. RESULTS: Controlling for gender and ethnicity, adolescents affiliating with the Burnouts reported more unhealthful eating and more bulimic behaviors than others; adolescents affiliating with the Brains reported more healthful eating, less unhealthful eating, and more dieting; those affiliating with Jocks and Populars reported engaging in more exercise; and Populars also reported more unhealthful eating. In addition, boys exercised more than girls; girls reported more dieting and bulimic behaviors. Black adolescents reported more unhealthful eating and less dieting than other adolescents. CONCLUSIONS: Along with gender and ethnicity, peer crowd affiliation is related to adolescents' eating, exercise, and weight control behaviors. Prevention programs should consider adolescent peer crowds in developing health promotion and obesity prevention programs.

Adolescent↗

PubMed1993

Crowding and contrast in amblyopia.

The crowding effect, defined as the ratio of visual acuities for letters presented in Snellen (i.e., line) format and isolated-letter format, was measured in the amblyopic eyes of 15 children and 15 adults with unilateral amblyopia. Normal limits were based on data from 20 children and 20 adults with no history of amblyopia. The crowding effect was compared for letters of high (96%) contrast and for letters of low (11%) contrast. We report that amblyopia can differentially affect line and isolated-letter acuity for both high- and low-contrast letters. For the patients that show an abnormal crowding effect, this effect can be: (1) significantly stronger, (2) significantly weaker, or (3) not significantly different for high- than for low-contrast letters. These findings are consistent with the hypothesis that the crowding effect is contrast-dependent in some amblyopic eyes of both child and adult unilateral amblyopes.

Adult↗

PubMed2006

Distraction osteogenesis in adolescents with maxillary arch deficiency and dental crowding: a 3-year follow-up.

BACKGROUND: In this study, the authors evaluated the long-term results after using anterior segmental osteotomy and distraction osteogenesis for the correction of sagittal maxillary deficiency associated with dental crowding. METHODS: Six young adolescents (four boys and two girls) underwent surgery and distraction at a mean age of 11.2 years (range, 10 to 12 years) and were followed up for 3 years. A tooth-borne distraction device was used for interdental distraction. The evaluation consisted of hard- and soft-tissue profile analysis and dental arch measurements before, immediately after, and 3 years after distraction. RESULTS: The results showed that the facial profile, the occlusion, and the dental crowding could be successfully corrected and that the results were stable after 3 years' follow-up. The mean facial convexity angle was changed from 1 to 8 degrees. The average advancement at point A was 4 mm and the SNA increased by an average of 4 degrees. Lengthening of the dental arch by an average of 4 mm created approximately 8 mm of new space, sufficient to resolve the dental crowding in all patients, thus avoiding an extraction of healthy teeth. CONCLUSION: The results of this study demonstrated that anterior segmental maxillary osteotomy combined with distraction osteogenesis offers an alternative for the treatment of adolescents suffering from sagittal maxillary deficiency with dental crowding.

Child↗

PubMed1988

Visual acuity testing of young children with the Cambridge Crowding Cards at 3 and 6 m.

A modification of the single optotype Sheridan Gardiner test for pre-school children has been used to measure visual crowding. A significant 'crowding effect' has been found in children between the ages of 3 and 6 years with a general decrease in the effect over the pre-school years. The 'crowding' in 5-7 year olds is not significantly greater than that found in adults. No significant difference has been found in the extent of crowding using the test at 3 m rather than the normal 6 m viewing distance, although in general the test has been found to be practically easier with better co-operation at 3 m for the younger children. For these reasons, this particular test at 3 m would seem to be well suited to acuity testing in pre-school children, when an acuity equivalent to Snellen values is required.

Adult↗

PubMed2006

Crowding, feature integration, and two kinds of "attention".

In a recent article, Pelli, Palomares, and Majaj (2004) suggested that feature binding is mediated by hard-wired integration fields instead of a spotlight of spatial attention (as assumed by Treisman & Gelade, 1980). Consequently, the correct conjoining of visual features can be guaranteed only when there are no other competing features within a circle with a radius of approximately 0.5E (E = eccentricity of the target object). This claim seems contradicted by an observation that we can easily see--for example, the orientation of a single blue bar within a dense array of randomly oriented red bars. In the present study, possible determinants of the extent of crowding (or feature integration) zones were analyzed with feature (color) singletons as targets. It was found that the number of distractors has a dramatic effect on crowding. With a few distractors, a normal crowding effect was observed. However, by increasing the number of distractors, the crowding effect was remarkably reduced. Similar results were observed when the target and distractors were of the same color and when only a differently colored circle indicated the target location. The results can be explained by bottom-up "attention" that facilitates the processing of information from salient locations in the visual field.

Attention↗

PubMed1995

Post-retention crowding and incisor irregularity: a long-term follow-up evaluation of stability and relapse.

The aim of the present long-term follow-up study of orthodontically-treated patients (mean: 15.7 years) was to analyse post-retention changes and to reveal factors which may play a role as predictors for long-term prognosis. Pretreatment, end-of-treatment, and post-retention models of 226 cases with all types of anomaly were used to measure intercanine and intermolar width, arch length, and sum of the mesiodistal dimension of the incisors, Irregularity Index, crowding, molar and canine relationship, overjet, and overbite. In order to assess the influence of sex, initial and end-of-treatment alignment, type of therapy, amount of tooth movement, and presence of third molars on the extent of post-retention changes, the total sample was divided into subgroups. Findings indicated that post-retention crowding and incisor irregularity increased more frequently in the mandible than in the maxilla. Pretreatment variables such as increased mesiodistal incisor dimension, severe crowding and incisor irregularity, arch length deficiency, arch constriction, and increased overbite as well as post-treatment spacing, arch expansion, increased arch length, and residual Class II or III molar relationships were found to be associated factors in the process of post-retention increase of crowding and incisor irregularity. 'Overexpansion' was found to be a factor in mandibular incisor relapse.

Analysis of Variance↗

PubMed1996

Late lower arch crowding in relation to skeletal and dental morphology and growth changes.

Skeletal and dental morphology, and related growth changes during a 3-year period following second permanent molar eruption, were compared in a group of 21 subjects who had no increase in lower arch crowding, with another group of 21 subjects whose lower arch crowding had increased by 1.0 mm or more during the same period. The crowding group showed a significantly greater increase in M3 space, forward movement of the second permanent molar and increase in the inter-incisal angle than the non-crowding group. None of the other parameters examined differed significantly.

Adolescent↗

PubMed2006

The association between emergency department crowding and hospital performance on antibiotic timing for pneumonia and percutaneous intervention for myocardial infarction.

BACKGROUND: Antibiotics within four hours of arrival for patients with pneumonia and percutaneous intervention (PCI) within two hours for patients with acute myocardial infarction (AMI) are standard measures of emergency department (ED) quality. OBJECTIVES: To assess the institutional-level association between measures of ED crowding and process measures for pneumonia and AMI. METHODS: The authors used summary data from 24 academic hospitals in the University Health Consortium. Analysis included the 2004 ED cycle time survey and performance data from January to December 2004 regarding the Joint Commission for Accreditation of Healthcare Organizations' PN-5b (initial antibiotic administration within four hours) for pneumonia and AMI-8a (PCI received within 120 minutes). Spearman correlation coefficients were used to determine associations between crowding and performance measures. RESULTS: Across all institutions, 59% (range 43%-77%) of pneumonia patients received antibiotics within four hours, and 57% (range 22%-95%) of AMI patients received PCI within two hours. An increase in overall ED length of stay (-0.44, p = 0.04) and for admitted patients (-0.37, p = 0.08) was associated with a decrease in the proportion of pneumonia patients receiving antibiotics within four hours. An increase in chest x-ray turnaround time (-0.83, p < 0.001) and an increase in the left-without-being-seen rate (-0.51, p = 0.01) were also associated with a decrease in the proportion of pneumonia patients receiving antibiotics within four hours. No measures of crowding exhibited an association with time to PCI for AMI patients. CONCLUSIONS: Administrative measures of ED crowding showed an association with poorer performance on pneumonia quality of care measures but not with AMI quality of care measures. Hospitals might consider improving ED throughput, reducing boarding times for admitted patients, and reducing chest x-ray turnaround times to improve pneumonia care.

Angioplasty, Balloon, Coronary↗

PubMed2002

The "crowding effect" in the cestode Schistocephalus solidus: density-dependent effects on plerocercoid size and infectivity.

The occurrence of the crowding effect was demonstrated in plerocercoids of the cestode Schistocephalus solidus infecting threespine stickleback Gasterosteus aculeatus from Walby and Scout lakes, Alaska. Contrary to an earlier report, relatively large numbers of parasites (>3-4 plerocercoids) were observed to grow large enough in an intermediate host fish to become competent to infect and to mature in the definitive host under any of 3 assumed threshold values and 1 scenario of graded sizes for parasite competency. In Walby Lake, intensity and host body mass were significant predictors of mean plerocercoid mass per host, whereas intensity, host body mass, and combined parasite index were significant predictors in Scout Lake. Slopes of equations expressing the relationship between mean parasite mass and intensity for both lakes were less than 1, implying that processes other than or in combination with simple resource limitation might be producing the observed crowding effect. The causal mechanism for the crowding effect could include exploitative competition, interference competition, and host immune response. There were significant differences in infection between the two lakes, including different distributions of parasite intensities among hosts and different expressions of the crowding effect; however, an explanation of the differences awaits further investigation.

Alaska↗