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PubMed1996

Site-directed mutagenesis of the CP 47 protein of photosystem II: 167W in the lumenally exposed loop C is required for photosystem II assembly and stability.

The intrinsic chlorophyll-protein CP 47 is a component of photosystem II which functions in both light-harvesting and oxygen evolution. Using site-directed mutagenesis we have produced the mutant W167S which lies in loop C of CP 47. This strain exhibited a 75% loss in oxygen evolution activity and grew extremely slowly in the absence of glucose. Examination of normalized oxygen evolution traces indicated that the mutant was susceptible to photoinactivation. Analysis of the variable fluorescence yield indicated that the mutant accumulated very few functional PS II reaction centers. This was confirmed by immunoblotting experiments. Interestingly, when W167S was grown in the presence of 20 microM DCMU, the mutant continued to exhibit these defects. These results indicate that tryptophan 167 in loop C of CP 47 is important for the assembly and stability of the PS II reaction center.

Cyanobacteria↗
PubMedDate not supplied

[Criteriological evolution in psychopathology].

Any theoretical direction in psychiatry takes into account a definition of the illness, and of the state of health and their limits, as well as the relationships between these two different states in their psychobehavioral expressiveness and within the relational system of personality. The states which are taken as deviations from what is generally considered and accepted as normal state, have always been identified and form the so-called major mental pathology, but one cannot ascertain the same thing about the so-called borderline states, and the representation of normality. It is also true that within the two international systems of classification, WHO and DSM-III one can find the difficulty and even the hesitation of using the term "mental illnesses" instead to use "mental disorders". These are the reasons that made the author consider useful the illustration of the diagnostic criterion through the classification of the concepts on mental illness--an evolution illustrated by the contribution of syndrome concepts, i.e. an anatomoclinical state according to the evolution of the symptoms, psychopathological criteria and generally the dimensional and categorical criteria. Thus, the criteriological investigation remains a theoretical actual approach and at the same time applicable for the psychiatric care.

History, 19th Century↗
PubMed2002

Feast and famine in plant genomes.

Plant genomes vary over several orders of magnitude in size, even among closely related species, yet the origin, genesis and significance of this variation are not clear. Because DNA content varies over a sevenfold range among diploid species in the cotton genus (Gossypium) and its allies, this group offers opportunities for exploring patterns and mechanisms of genome size evolution. For example, the question has been raised whether plant genomes have a 'one-way ticket to genomic obesity', as a consequence of retroelement accumulation. Few empirical studies directly address this possibility, although it is consistent with recent insights gleaned from evolutionary genomic investigations. We used a phylogenetic approach to evaluate the directionality of genome size evolution among Gossypium species and their relatives in the cotton tribe (Gossypieae, Malvaceae). Our results suggest that both DNA content increase and decrease have occurred repeatedly during evolution. In contrast to a model of unidirectional genome size change, the frequency of inferred genome size contraction exceeded that of expansion. In conjunction with other evidence, this finding highlights the dynamic nature of plant genome size evolution, and suggests that poorly understood genomic contraction mechanisms operate on a more extensive scale that previously recognized. Moreover, the research sets the stage for fine-scale analysis of the evolutionary dynamics and directionality of change for the full spectrum of genomic constituents.

Chromosomes↗
PubMed2003

Resonant double excitation observed in the near-threshold evolution of the photoexcited F K alpha satellite intensity in NaF.

We present a precise measurement of the photoexcited F K alpha satellite intensity's evolution for NaF from [1s2p] double excitation threshold to saturation. A direct comparison between the observed evolution and the x-ray absorption spectrum was successfully made, and the contribution of multielectron transitions to the absorption spectrum was clearly resolved for the first time. A resonance-like feature observed in the near-threshold evolution is attributed to the [1s2p]3p(2) resonant double excitation as confirmed by calculations.

Journal Article↗
PubMed1997

Applications of peptide synthetases in the synthesis of peptide analogues.

Enzymatically formed peptides show positional variations as well as highly conserved amino acids. In the cases of gramicidin S, tyrocidine, linear gramicidins, enniatins, echinocandins and viridogrisein in vivo and in vitro studies indicate substrate selection at the level of amino acid activation as a major control step. Evidence for proof-reading steps beyond activation has been obtained in penicillin and cyclosporin biosynthesis. Activated substrate analogues may promote the formation of side products such as dipeptides and cyclodipeptides. Modifications of intermediates, such as N-methylation, influence the rates of peptide synthesis. These control steps pose limitations for the application of such enzyme systems in the production of peptide libraries. They may originate from a target oriented evolution of these synthetases.

Amino Acid Sequence↗
PubMed2003

Engineered enzymes for improved organic synthesis.

Recent developments to modify enzymes for use in organic synthesis have targeted several areas. These include altering the reaction mechanism of the enzyme to catalyse new reactions, switching substrate specificity, expanding substrate specificity, and improving substrate specificity, such as enantioselectivity in kinetic resolutions. Such modifications can be achieved either by rational redesign, which requires knowledge of the enzyme structure, or by random mutagenesis methods followed by screening. Both strategies of enzyme engineering can be successful and are very useful for improving the utility of enzymes for applied catalysis. Several examples illustrating these concepts in a variety of enzyme classes have appeared recently.

Catalysis↗
PubMed2002

3D HSQC-HSQMBC--increasing the resolution of long-range proton-carbon correlation experiments.

A 3D HSQC-HSQMBC experiment is proposed for increasing the separation of proton-carbon long-range correlation cross peaks, the lack of which is occasionally seen in corresponding 2D experiments. It is aimed at complex molecules with many protonated carbons exhibiting a narrow spread of 13C chemical shifts e.g., complex carbohydrates. It does not yield long-range correlation of quaternary carbons. An extra indirectly detected 1H dimension of this experiment provides additional separation of long-range correlation cross peaks by utilising the chemical shifts of protons directly attached to 13C. Evolution of single-quantum coherences throughout the entire pulse sequence ensures that the cross peaks are inphase pure absorption singlets in both indirectly detected dimensions, thus maximising the resolution and sensitivity of the experiment. Partial signal cancellation can be expected due to the antiphase character of peaks in the directly detected dimension. The intensity of cross peaks depends on the length of a single long-range evolution interval and values of both active and passive long-range coupling constants of each carbon. The 3D HSQC-HSQMBC experiment provided high quality long-range correlation spectra of a 2 mg pentasaccharide sample in 27 h. The technique can also be used for measurement of long-range heteronuclear coupling constants from pure antiphase multiplets in the directly detected dimension.

Carbon↗
PubMed1998

Environmentally responsive mutator systems: toward a unifying perspective.

Biology has long sought a unifying principle. The behaviour of genetically controlled mutator processes adaptively responsive to stress may reflect such a principle. Related mutators exist in diverse organisms from bacteria to mammals. Such systems have evolved from one another and have defined the very evolution of organisms. Many of these mutator systems can determine in a developmental manner a ultramutability or hypermutability throughout the genome. Though the genetic control of high levels of mutability can reflect molecular features, such mutagenic processes reflect a deeper parameter involving forces and their configurations. These configurations must generate stable or uniform configurations from unstable ones throughout the genome and organism. Directed mutation becomes a generative process attuned to non-uniform forces of local niches and to the more uniform forces of a universal niche. The manner of mutagenic, attuned response depends on the level of genomic and transgenomic organization. This is reflected in hierarchies of evolution. Directed mutation is a feature of a universal, generative ordering process, and this feature is marked by a universal dimensionless constant. It is the dynamic consequence of such directed generation which ultimately confers adaptation through dynamic completion. This suggests an underlying, unitary, and necessary dynamics connecting ultramutability systems in all organisms and would serve, in complementation with a molecular approach, to elicit new and productive research avenues. One outcome would be the illustration of a unifying principle governing biological and physical phenomena.

Adaptation, Physiological↗
PubMed2005

The convoluted evolution of snail chirality.

The direction that a snail (Mollusca: Gastropoda) coils, whether dextral (right-handed) or sinistral (left-handed), originates in early development but is most easily observed in the shell form of the adult. Here, we review recent progress in understanding snail chirality from genetic, developmental and ecological perspectives. In the few species that have been characterized, chirality is determined by a single genetic locus with delayed inheritance, which means that the genotype is expressed in the mother's offspring. Although research lags behind the studies of asymmetry in the mouse and nematode, attempts to isolate the loci involved in snail chirality have begun, with the final aim of understanding how the axis of left-right asymmetry is established. In nature, most snail taxa (>90%) are dextral, but sinistrality is known from mutant individuals, populations within dextral species, entirely sinistral species, genera and even families. Ordinarily, it is expected that strong frequency-dependent selection should act against the establishment of new chiral types because the chiral minority have difficulty finding a suitable mating partner (their genitalia are on the 'wrong' side). Mixed populations should therefore not persist. Intriguingly, however, a very few land snail species, notably the subgenus Amphidromus sensu stricto, not only appear to mate randomly between different chiral types, but also have a stable, within-population chiral dimorphism, which suggests the involvement of a balancing factor. At the other end of the spectrum, in many species, different chiral types are unable to mate and so could be reproductively isolated from one another. However, while empirical data, models and simulations have indicated that chiral reversal must sometimes occur, it is rarely likely to lead to so-called 'single-gene' speciation. Nevertheless, chiral reversal could still be a contributing factor to speciation (or to divergence after speciation) when reproductive character displacement is involved. Understanding the establishment of chirality, the preponderance of dextral species and the rare instances of stable dimorphism is an important target for future research. Since the genetics of chirality have been studied in only a few pulmonate species, we also urge that more taxa, especially those from the sea, should be investigated.

Animal Structures↗
PubMed2005

Planet of the apes.

What makes us humans so special? Our language, our genes, our culture, our cognitive skills? At the Max-Planck-Institute for Evolutionary Anthropology in Leipzig, psychologists, linguists and biologists tackle this old question in a truly multidisciplinary way. Their results have implications not just for our understanding of human evolution--they also touch directly on many social and environmental issues. Florian Maderspacher reports.

Academies and Institutes↗
PubMed2001

An in vitro DNA virus for in vitro protein evolution.

In vitro virus is a molecular construct for in vitro protein evolution, which requires some mechanism to link phenotype to genotype. The first in vitro virus was realized by bonding a nascent protein with its coding mRNA via puromycin in in vitro translation. We report a new construct of in vitro DNA virus. The virion was a covalent cDNA-protein fusion, and virion formation did not require any modification of mRNA. Due to intactness of mRNA, this type of in vitro DNA virus will take the next step toward in vitro autonomous evolution, just like in vivo viral evolution in a cellstat.

DNA Primers↗
PubMed2001

In vitro enzyme evolution: the screening challenge of isolating the one in a million.

The generation of large mutant libraries for in vitro enzyme evolution presents the challenge of effectively screening libraries of 10(4)-10(7) mutants on the basis of simultaneously assaying their biocatalytic activity. In this review, we highlight the main steps involved in this process, describe the alternative approaches to address this challenge, survey the state-of-the-art technology and assess achievements already made. It is anticipated that, as a result of the expected accomplishment of further improvements in high-throughput screening that will allow routine screening of whole libraries, the number of useful new and improved enzymes derived through in vitro enzyme evolution will expand rapidly in the near future.

Cells, Immobilized↗
PubMedDate not supplied

[Probability of a "greenhouse catastrophe" and the nature of feedback].

The chance of "hotbed catastrophe" appearance is discussed on the theoretical base. The feedbacks have essential significance in ecological and evolutional processes. They are directed against the cause, which disturb the status of ecological equilibrium in biosystem always. The "hotbed effect" will provoke biospherical processes, which will be directed to the reconstruction of ecological equilibrium status. "Hotbed catastrophe" chance is very small.

Biological Evolution↗
PubMed2025

An orthogonal T7 replisome for continuous hypermutation and accelerated evolution in E. coli.

Systems that perform continuous hypermutation of designated genes without compromising the integrity of the host genome can substantially accelerate the evolution of new or enhanced protein functions. We describe an orthogonal DNA replication system in Escherichia coli based on the controlled expression of the replisome of bacteriophage T7 (T7-ORACLE). The system replicates circular plasmids that enable high transformation efficiencies and seamless integration into standard molecular biology workflows. Engineering of T7 DNA polymerase yielded variant proteins with mutation rates of 1.7 × 10-5 substitutions per base in vivo-100,000-fold above the genomic mutation rate. We demonstrated continuous evolution using the T7 replisome by expanding the substrate scope of TEM-1 β-lactamase and increasing activity 5000-fold against clinically relevant monobactam and cephalosporin antibiotics in less than 1 week.

Bacteriophage T7↗
PubMedDate not supplied

mtDNA ribosomal gene phylogeny of sea hares in the genus Aplysia (Gastropoda, Opisthobranchia, Anaspidea): implications for comparative neurobiology.

Sea hares within the genus Aplysia are important neurobiological model organisms; as more studies based on different Aplysia species are appearing in the literature, a phylogenetic framework has become essential. We present a phylogenetic hypothesis for this genus, based on portions of two mitochondrial genes (12S and 16S). In addition, we reconstruct the evolution of several behavioral characters of interest to neurobiologists to illustrate the potential benefits of a phylogeny for the genus Aplysia. These benefits include determination of ancestral traits, direction and timing of evolution of characters, prediction of the distribution of traits, and identification of cases of independent acquisition of traits within lineages. This last benefit may prove especially useful in understanding the linkage between behaviors and their underlying neurological bases.

Animals↗
PubMed2002

Increasing the thermal stability of an oligomeric protein, beta-glucuronidase.

The reporter enzyme beta-glucuronidase was mutagenized and evolved for thermostability. After four cycles of screening the best variant was more active than the wild-type enzyme, and retained function at 70 degrees C, whereas the wild-type enzyme lost function at 65 degrees C. Variants derived from sequential mutagenesis were shuffled together, and re-screened for thermostability. The best variants retained activities at even higher temperatures (80 degrees C), but had specific activities that were now less than that of the wild-type enzyme. The mutations clustered near the tetramer interface of the enzyme, and many of the evolved variants showed much greater resistance to quaternary structure disruption at high temperatures, which is also a characteristic of naturally thermostable enzymes. Together, these results suggest a pathway for the evolution of thermostability in which enzymes initially become stable at high temperatures without loss of activity at low temperatures, while further evolution leads to enzymes that have kinetic parameters that are optimized for high temperatures.

Directed Molecular Evolution↗