36 research outputs found
Analytical Approaches for Deriving Friction Coefficients for Selected α‑Helical Peptides Based Entirely on Molecular Dynamics Simulations
In this paper we derive analytically from molecular dynamics (MD) simulations the friction coefficients related to conformational transitions within several model peptides with α-helical structures. We study a series of alanine peptides with various length from ALA5 to ALA21 as well as their two derivatives, the (AAQAA)3 peptide and a 13-residue KR1 peptide that is a derivative of the (AAQAA)2 peptide with the formula GN(AAQAA)2G. We use two kinds of approaches to derive their friction coefficients. In the local approach, friction associated with fluctuations of single hydrogen bonds are studied. In the second approach, friction coefficients associated with a folding transitions within the studied peptides are obtained. In both cases, the respective friction coefficients differentiated very well the subtle structural changes between studied peptides and compared favorably to experimentally available data
Length Dependent Folding Kinetics of Alanine-Based Helical Peptides from Optimal Dimensionality Reduction
We present a computer simulation study of helix folding in alanine homopeptides (ALA)n of length n = 5, 8, 15, and 21 residues. Based on multi-microsecond molecular dynamics simulations at room temperature, we found helix populations and relaxation times increasing from about 6% and ~2 ns for ALA5 to about 60% and ~500 ns for ALA21, and folding free energies decreasing linearly with the increasing number of residues. The helix folding was analyzed with the Optimal Dimensionality Reduction method, yielding coarse-grained kinetic models that provided a detailed representation of the folding process. The shorter peptides, ALA5 and ALA8, tended to convert directly from coil to helix, while ALA15 and ALA21 traveled through several intermediates. Coarse-grained aggregate states representing the helix, coil, and intermediates were heterogeneous, encompassing multiple peptide conformations. The folding involved multiple pathways and interesting intermediate states were present on the folding paths, with partially formed helices, turns, and compact coils. Statistically, helix initiation was favored at both termini, and the helix was most stable in the central region. Importantly, we found the presence of underlying universal local dynamics in helical peptides with correlated transitions for neighboring hydrogen bonds. Overall, the structural and dynamical parameters extracted from the trajectories are in good agreement with experimental observables, providing microscopic insights into the complex helix folding kinetics
Biological indices applied to benthic macroinvertebrates at reference conditions of mountain streams in two ecoregions (Poland, the Slovak Republic)
The study was carried out from 2007 to
2010 in two ecoregions: the Carpathians and the
Central Highlands. The objectives of our survey were
to test the existing biological index metric based on
benthic macroinvertebrates at reference conditions in
the high- and mid-altitude mountain streams of two
ecoregions according to the requirements of the EU
WFD and to determine which environmental factors
influence the distribution of benthic macroinvertebrates.
Our results revealed statistically significant
differences in the values of the physical and chemical
parameters of water as well as the mean values of
metrics between the types of streams at the sampling
sites. RDA analysis showed that the temperature of the
water, pH, conductivity, the stream gradient, values of
the HQA index, and altitude were the parameters most
associated with the distribution of benthic macroinvertebrate
taxa and the values of the metrics. The
values of biological indices should be considered
according to the stream typology including altitude
and geology. At the reference conditions, the suggested
border values of biological indices are very
harsh. The values of the biological indices of most
sampling sites did not correspond to the requirements
of the high status in rivers. The streams at altitudes
above 1,200 m a.s.l. should be treated as another river
type and new reference values should be established
Development of comprehensive river typology based on macrophytes in the mountain-lowland gradient of different Central European ecoregions
The aim of the study was to identify the vegetation pattern in the different types of watercourses basing on survey in reference conditions in a wide geographical gradient, including mountain, upland and lowland rivers. We tested relationship between composition of macrophytes to environmental variables including: altitude, slope, catchment area, geology of valley, land use, hydromorphological sfeatures, water physical and chemical measurements. Analysis based on 109 pristine river sites located throughout major types of rivers in Central Europe. Qualitative and quantitative plant surveys were carried out between 2005 and 2013. Based on TWINSPAN classification and DCA analysis, six macrophyte types were distinguished. The lowland sites were divided into the following three types: humic rivers and two types of siliceous rivers depending on the catchment area, including medium-large and small rivers. The mountain and upland rivers were divided into three geological types: siliceous, calcareous and gravel. We found that the variation of macrophyte communities was determined by several habitat factors (mainly altitude, flow type, riverbed granulometry, conductivity and alkalinity), whereas the spatial factor was rather limited; further, the plant diversity was not reflected accurately by the European ecoregion approach
Macrophyte and macroinvertebrate patterns in unimpacted mountain rivers of two European ecoregions
The aim of the study was to compare the
patterns of development of macrophytes and macroinvertebrates
in different types of reference mountain
rivers. The study is based on reference river sites
surveyed throughout the mountains in Poland and
Slovakia in two European ecoregions (9—Central
Highlands, 10—The Carpathians). A wide range of
environmental variables were estimated, including
water chemistry, hydromorphology, geology, and the
spatial factor. Based on the Jaccard index, macrophyte
and macroinvertebrate variation was confirmed
between four mountain and upland river types. It
was found that the biological diversification is mainly
influenced by geological and associated chemical
factors. In the case of macroinvertebrates, additionally,
the importance of the spatial factor was revealed
(difference between ecoregions). Finally, the habitat
preferences of various taxa were identified. It was
found that extreme mountain conditions can sometimes
distort bioindicative response, as was detected in
the case of macroinvertebrates in the highest mountain
sites. We concluded that consideration of two groups
of organisms enables more comprehensive and reliable
monitoring than assessment based on a single
group, especially when standard bioindicative methods
can be distorted by extreme local conditions
Biological indices applied to benthic macroinvertebrates at reference conditions of mountain streams in two ecoregions (Poland, the Slovak Republic)
Plants in aquatic ecosystems: current trends and future directions
Aquatic plants fulfil a wide range of ecological roles, and make a substantial contribution to the structure, function and service provision of aquatic ecosystems. Given their well-documented importance in aquatic ecosystems, research into aquatic plants continues to blossom. The 14th International Symposium on Aquatic Plants, held in Edinburgh in September 2015, brought together 120 delegates from 28 countries and six continents. This special issue of Hydrobiologia includes a select number of papers on aspects of aquatic plants, covering a wide range of species, systems and issues. In this paper we present an overview of current trends and future directions in aquatic plant research in the early 21st century. Our understanding of aquatic plant biology, the range of scientific issues being addressed and the range of techniques available to researchers have all arguably never been greater; however, substantial challenges exist to the conservation and management of both aquatic plants and the ecosystems in which they are found. The range of countries and continents represented by conference delegates and authors of papers in the special issue illustrate the global relevance of aquatic plant research in the early 21st century but also the many challenges that this burgeoning scientific discipline must address