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PubMed2000

Macromolecular crowding and its consequences.

Incompatible pairs of polymers separate into two phases in aqueous solution above a few percentage points total concentration. Protein pairs can also produce phase separation, but at somewhat higher concentrations. In this chapter, we explore the effect of high background concentrations of macromolecules on phase separation of pairs of species which would not be at sufficiently high concentration to separate in the absence of the uninvolved species. Effects produced by such high background concentrations are known as macromolecular crowding. Dramatic enhancements in various association reactions due to crowding have been predicted and observed but its effects on phase separation in biological mixtures typical of the cytoplasm have not been examined. Here, we describe a calculation based on the Flory-Huggins treatment of concentrated polymer solutions that sheds some light on this issue. We find that a background of 20 wt % of a high molecular weight species greatly reduces the concentrations needed to produce phase separation in a mixture of two incompatible macromolecules if one is more hydrophobic than the other. Given the high total concentration of macromolecules in cytoplasm, it is perhaps surprising that phases have not been observed. This issue is discussed and some explanations offered.

Bacterial Proteins↗
PubMed2006

Finding a face in the crowd: parallel and serial neural mechanisms of visual selection.

At any given moment, our visual system is confronted with more information than it can process. Thus, attention is needed to select behaviorally relevant information in a visual scene for further processing. Behavioral studies of attention during visual search have led to the distinction between serial and parallel mechanisms of selection. To find a target object in a crowded scene, for example a "face in a crowd", the visual system might turn on and off the neural representation of each object in a serial fashion, testing each representation against a template of the target object. Alternatively, it might allow the processing of all objects in parallel, but bias activity in favor of those neurons representing critical features of the target, until the target emerges from the background. Recent neurophysiological evidence shows that both serial and parallel selections take place in neurons of the ventral "object-recognition pathway" during visual search tasks in which monkeys freely scan complex displays to find a target object. Furthermore, attentional selection appears to be mediated by changes in the synchrony of responses of neuronal populations in addition to the modulation of the firing rate of individual neurons.

Animals↗
PubMed1997

Clinical relevance of third permanent molars in relation to crowding after orthodontic treatment.

OBJECTIVES: The purpose of this study was to determine the relationship between dental crowding and the clinical presence or absence of third permanent molar teeth. METHODS: Ninety-nine patients were analysed before and after orthodontic treatment and at least three years after the end of retention. The sample consisted of four groups: subjects whose third permanent molar teeth had erupted into the mouth, were non-erupted, were extracted, and were congenitally absent. Arch Length Discrepancy, Irregularity Index and observer bias were examined. Multivariate analysis of variance with repeated measurements was used to analyse differences between the four groups. RESULTS: Significant differences in Arch Length Discrepancy during time were shown between the premolar segment and the frontal area. The group with third permanent molar teeth congenitally missing showed a significant higher positive Arch Length Discrepancy in the premolar segment of the upper jaw. No significant differences in Irregularity Index were found between the third molar groups. CONCLUSIONS: It can be concluded that there is no relation between crowding and the presence or absence of third permanent molar teeth.

Adolescent↗
PubMed2002

Efficacy of macromolecular crowding in forcing proteins to fold.

The intrinsically unstructured protein, reduced and carboxyamidated RNase T1 (TCAM) was used to determine the degree to which macromolecular crowding agents increase the equilibrium constant for folding. TCAM is not catalytically active in an aqueous assay system alone, but becomes catalytically active on addition of 400 mg/ml dextran 70. The activity observed accounts for approximately 16% of the total available TCAM in solution. We interpret this result to mean that 16% of the TCAM becomes folded protein in the presence of the 400 mg/ml dextran 70, and this translates into an approximately five-fold increase in the equilibrium constant for folding. Sarcosine-induced folding of TCAM was performed in the presence of 0, 100, 200 and 300 mg/ml dextran 70, and apparent deltaG(o)(N-D) values determined from the linear extrapolation method provide an estimated 22% folded TCAM formed in the limit of zero sarcosine concentration and in presence of 400 mg/ml dextran 70. The increase in TCAM folding equilibrium constant using this method of determination is approximately 7.5-fold. Overall, the results indicate that macromolecular crowding agents are only modestly effective in promoting folding of this intrinsically unstructured protein.

Catalysis↗
PubMed2003

Proteins, channels and crowded ions.

Ion channels are proteins with a hole down their middle that control a vast range of biological function in health and disease. Selectivity is an important biological function determined by the open channel, which does not change conformation on the biological time scale. The challenge is to predict the function-the current of ions of different types and concentrations through a variety of channels-from structure, given fundamental physical laws. Walls of ion channels, like active sites of enzymes, often contain several fixed charges. Those fixed charges demand counter ions nearby, and the density of those counter ions is very high, greater than 5 molar, because of the tiny volumes of the channel's pore. Physical chemists can now calculate the free energy per mole of salt solutions (e.g. the activity coefficient) from infinite dilution to saturation, even in ionic melts. Such calculations of a model of the L-type calcium channel show that the large energies needed to crowd charges into the channel can account for the substantial selectivity and complex properties found experimentally. The properties of such crowded charge are likely to be an important determinant of the properties of proteins in general because channels are nearly enzymes.

Animals↗
PubMed1993

An American Board of Orthodontics case report: treatment of a crowded Class II malocclusion in an adult.

A case report is presented of an adult with a crowded Class II, Division I subdivision left malocclusion. There was a moderate arch length deficiency in both arches. All four canines were prominent and had gingival recession. The patient's profile necessitated nonextraction treatment. Free gingival grafts were placed to prevent further recession and the Class II relationship and crowding were resolved with a positive profile change. [This case was presented to the American Board of Orthodontics in partial fulfillment of the requirements for the certification process conducted by the board.]

Adult↗
PubMed1994

The etiology of late lower arch crowding alternative to mesially directed forces: a review.

The causes of late crowding in the lower arch alternative to mesially directed forces are reviewed under the headings: late mandibular growth, skeletal structure and complex growth pattern, soft tissue maturation, periodontal forces, tooth structure, occlusal factors, and connective tissue changes. A multifactorial basis for late lower arch crowding seems likely.

Adolescent↗
PubMed1997

Late lower arch crowding in relation to soft tissue maturation.

Changes in lower arch space condition and incisor inclinations were measured in relation to changes in the cross-sectional area and separation of the lips in habitual posture in 23 boys and 23 girls between the ages of 12.5 and 15.5 years. Correlation analysis revealed no direct relationship between the increase in lower arch crowding and the changes in lip size and position. In girls, the increase in lower arch crowding was associated to some extent with retroclination of the upper incisors and an increase in the interincisal angle. A very tenuous relationship was found between changes in the upper lip size and position and changes in incisor angulation.

Adolescent↗
PubMed2001

Macromolecular crowding: an important but neglected aspect of the intracellular environment.

Biological macromolecules have evolved over billions of years to function inside cells, so it is not surprising that researchers studying the properties of such molecules, either in extracts or in purified form, take care to control factors that reflect the intracellular environment, such as pH, ionic strength and composition, redox potential and the concentrations of relevant metabolites and effector molecules. There is one universal aspect of the cellular interior, however, that is largely neglected--the fact that it is highly crowded with macromolecules. It is proposed that the addition of crowding agents should become as routine as controlling pH and ionic strength if we are to meet the objective of studying biological molecules under more physiologically relevant conditions.

Chaperonins↗
PubMed2000

Implications of macromolecular crowding for protein assembly.

Recent studies have led to increased appreciation of the influence of excluded volume in solutions of high total macromolecular content ('macromolecular crowding') upon the various classes of reaction that lead to the assembly of proteins and protein complexes. In general, crowding is expected to stabilize native protein structure relative to less compact non-native structures and to favor the formation of functional complexes of native proteins. Under certain pathological conditions, 'overcrowding' may enhance the formation of nonfunctional aggregates of non-native protein (e.g. amyloid and inclusion bodies).

Adenosine Triphosphate↗
PubMed1997

Molecular chaperones: avoiding the crowd.

The involvement of two types of molecular chaperone in folding newly synthesized proteins can be rationalized in terms of the crowded nature of the intracellular environment. Recent work sheds light on how these chaperones recognise their substrates and protect them from the problems of macromolecular crowding.

Animals↗
PubMed2001

Macromolecular crowding and its role as intracellular signalling of cell volume regulation.

Macromolecular crowding has been proposed as a mechanism by means of which a cell can sense relatively small changes in volume or, more accurately, the concentration of intracellular solutes. According to the macromolecular theory, the kinetics and equilibria of enzymes can be greatly influenced by small changes in the concentration of ambient, inert macromolecules. A 10% change in the concentration of intracellular proteins can lead to changes of up to a factor of ten in the thermodynamic activity of putative molecular regulatory species, and consequently, the extent to which such regulator(s) may bind to and activate membrane-associated ion transporters. The aim of this review is to examine the concept of macromolecular crowding and how it profoundly affects macromolecular association in an intact cell with particular emphasis on its implication as a sensor and a mechanism through which cell volume is regulated.

Animals↗
PubMed2006

Crowding effect on adult growth, pre-patent period and egg shedding of Fasciola hepatica.

Fascioliasis pathogenesis depends on fluke burden. In human hyperendemic zones, individual infection intensities reach very high levels and the majority of infected subjects should be in the advanced chronic phase. The rat model offers a useful approach for pathological research in the advanced chronic period. The influence of infection intensity per rat on fluke development, pre-patent period and egg shedding (eggs/g faeces/worm) was analysed in 3 groups (I: 1-3 worms/rat; II: 4-6; III: 7-9). Ontogenetic trajectories of fluke body measures followed a logistic model. Results showed that when the burden increases, the maximum values of fluke measures decrease. The crowding effect is manifest when fluke measures approximate their maximums in the advanced chronic stage. The pre-patent period and egg production decrease when the burden increases. This means that measurements of eggs per gramme of faeces tend to underestimate the fluke burden. The present study demonstrates how to quantify the fascioliasis experimental rat model crowding effect on adult growth, pre-patent period and egg production. This quantification may be of great interest in epidemiological studies and in experimental research on the in vivo actions of different anthelminthic drugs and vaccines, pathology, immunology and resistance studies.

Animals↗
PubMed2003

Roles of cytoplasmic osmolytes, water, and crowding in the response of Escherichia coli to osmotic stress: biophysical basis of osmoprotection by glycine betaine.

To better understand the biophysical basis of osmoprotection by glycine betaine (GB) and the roles of cytoplasmic osmolytes, water, and macromolecular crowding in the growth of osmotically stressed Escherichia coli, we have determined growth rates and amounts of GB, K(+), trehalose, biopolymers, and water in the cytoplasm of E. coli K-12 grown over a wide range of high external osmolalities (1.02-2.17 Osm) in MOPS-buffered minimal medium (MBM) containing 1 mM betaine (MBM+GB). As osmolality increases, we observe that the amount of cytoplasmic GB increases, the amounts of K(+) (the other major cytoplasmic solute) and of biopolymers remain relatively constant, and the growth rate and the amount of cytoplasmic water decrease strongly, so concentrations of biopolymers and all solutes increase with increasing osmolality. We observe the same correlation between the growth rate and the amount of cytoplasmic water for cells grown in MBM+GB as in MBM, supporting our proposal that the amount of cytoplasmic water is a primary determinant of the growth rate of osmotically stressed cells. We also observe the same correlation between cytoplasmic concentrations of biopolymers and K(+) for cells grown in MBM and MBM+GB, consistent with our hypothesis of compensation between the anticipated large perturbing effects on cytoplasmic protein-DNA interactions of increases in cytoplasmic concentrations of K(+) and biopolymers (crowding) with increasing osmolality. For growth conditions where the amount of cytoplasmic water is relatively large, we find that cytoplasmic osmolality is adequately predicted by assuming that contributions of individual solutes to osmolality are additive and using in vitro osmotic data on osmolytes and a local bulk domain model for cytoplasmic water. At moderate growth osmolalities (up to 1 Osm), we conclude that GB is an efficient osmoprotectant because it is almost as excluded from the biopolymer surface in the cytoplasm as it is from native protein surface in vitro. At very high growth osmolalities where cells contain little cytoplasmic water, predicted cytoplasmic osmolalities greatly exceed observed osmolalities, and the efficiency of GB as an osmolality booster decreases as the amount of cytoplasmic water decreases.

Betaine↗
PubMed2003

Comparative reactivity of sterically crowded nf3 (C5Me5)3Nd and (C5Me5)3U complexes with CO: formation of a nonclassical carbonium ion versus an f element metal carbonyl complex.

Sterically crowded isoelectronic nf(3) (C(5)Me(5))(3)M complexes of neodymium and uranium, compounds which have unconventionally long metal ligand distances, are found to react very differently with CO as a substrate. The 4f(3) complex (C(5)Me(5))(3)Nd reacts with CO to form a nonclassical carbonium ion complex, (C(5)Me(5))(2)Nd(O(2)C(7)Me(5)), which contains a three-coordinate planar carbon. (C(5)Me(5))(3)U reacts with CO to form an even more crowded CO adduct through a reaction type never observed before for (C(5)Me(5))(3)M compounds. The rare uranium carbonyl complex, (C(5)Me(5))(3)U(CO), has nu(CO) = 1922 cm(-1) and a U-C(CO) distance of 2.485(9) A.

Journal Article↗
PubMed2003

Sterically crowded bicyclo[1.1.0]butane radical cations.

The variability of carbon-carbon single bonds by steric and electronic effects is probed by DFT calculations of sterically crowded bicyclo[1.1.0]butanes and their radical cations. The interplay of sterics and electronics on the gradual weakening and breaking of bonds was studied by investigating bridgehead substitution in 1,3-di-tert-butylbicyclo[1.1.0]butane and 2,2',4,4'-tetramethyl-1,3-di-tert-butylbicyclo[1.1.0]butane and geminal substitution in 2,2'-di-tert-butylbicyclo[1.1.0]butane and 2,2',4,4'-tetra-tert-butylbicyclo[1.1.0]butane. Bridgehead substitution leads to a lengthening of the central bond, whereas bisubstitution on the geminal carbon leads to a shortening of this bond due to a Thorpe-Ingold effect. Although the character of the central bond can be modulated by substitution and electron transfer over a range of 0.35 A, the state forbidden ring planarization does not occur. Sterically crowded bicyclo[1.1.0]butane radical cations are therefore promising candidates for the investigation of extremely long carbon-carbon single bonds.

Journal Article↗
PubMed2003

Quantitative variation of four morphological traits in Drosophila melanogaster under larval crowding.

Effects of three different larval densities (low, intermediate and high) on phenotypic and genetic variation of four morphological traits (thorax and wing length, sternopleural and abdominal bristle number) were studied in Drosophila melanogaster using the isofemale line technique. Phenotypic variation was found to increase at high larval density in all traits examined. Environmental variance for three traits (exception was sternopleural bristle number) and fluctuating asymmetry for both bilateral traits were also increased under high density conditions. For estimates of genetic variability (among isofemale lines variance, heritability and evolvability), no statistically significant differences among density regimes were detected. However, the trends in changes of these estimates across densities indicated a possibility for enhanced genetic variation under larval crowding for all traits except abdominal bristle number. For the latter trait, genetic variation seemed not to be dependent on density regime. Generally, two metric traits (thorax and wing length) were more affected by larval crowding than two meristic ones (sternopleural and abdominal bristle number). The Results are in complete agreement with those previously obtained for D. melanogaster using extreme temperatures as stress-factors.

Abdomen↗
PubMed1988

Finding the face in the crowd: an anger superiority effect.

Facial gestures have been given an increasingly critical role in models of emotion. The biological significance of interindividual transmission of emotional signals is a pivotal assumption for placing the face in a central position in these models. This assumption invited a logical corollary, examined in this article: Face-processing should be highly efficient. Three experiments documented an asymmetry in the processing of emotionally discrepant faces embedded in crowds. The results suggested that threatening faces pop out of crowds, perhaps as a result of a preattentive, parallel search for signals of direct threat.

Anger↗