Tree ring anatomy indices of Pinus tabuliformis revealed the shifted dominant climate factor influencing potential hydraulic function in western Qinling Mountains

Trees can adjust xylem anatomical structure related with potential hydraulic functions to cope with climate variability. We therefore need a better understanding of how climate variability constrains wood anatomy and tree radial growth. Pinus tabuliformis dominates natural forests and plantations over the western Qinling Mountains, which is one of the ecologically vulnerable areas in China. Here, we investigated the response of P. tabuliformis tree-ring anatomical structure to climate variability by applying wood anatomy analysis, and evaluated the influences of anatomical traits on potential hydraulic functions and the climate significance of intra-annual density fluctuations (IADFs). We found that with the increasing temperature from spring to summer, the negative effect of temperature on the formation and enlargement of earlywood and transition-wood tracheids was gradually enhanced. However, spring precipitation not only had a direct and positive influence on the formation of earlywood, but also had a delaying impact on the transition-wood cell enlargement. Besides, the smaller earlywood tracheid size of P. tabuliformis could be a substantially characteristic reflecting spring drought. The contribution of lumen diameter on conduit wall reinforcement was dominated in earlywood, while the contribution of cell wall thickness was greater than that of lumen diameter in latewood. The different contributions of anatomical traits on conduit wall reinforcement would further affect the response of potential hydraulic function to climate. IADFs of P. tabuliformis could be a potential indicator to reflect the abnormal summer precipitation events in the western Qinling Mountains. IADFs with strong and weak intensity indicated years with high and low rates of change in mid-summer precipitation, respectively. Future warmer and drier climate in the western Qinling Mountains will likely result in the production of smaller tracheids to ensure hydraulic safety, which means the stronger drought resistant of P. tabuliformis in the future. In this study, we linked the xylem anatomy and potential hydraulics functions with intra-seasonal climate variability in the context of climate warming and drying, and proposed some xylem anatomical indices reflecting potential drought events.     

Additives and Enzyme Stability

The polypeptide chain of an enzyme is folded so that the necessary functional groups are brought together in the active site. Conformational changes may disrupt this arrangement and cause loss of enzymic activity. The effect of soluble additives on the unfolding process is discussed. Additives may be classified as substrates and similar ligands, small uncharged organic molecules, specific and non-specific ionic species, and polymers.     

Microsecond Dynamics During the Binding-induced Folding of an Intrinsically Disordered Protein

Tau is an intrinsically disordered protein implicated in many neurodegenerative diseases. The repeat domain fragment of tau, tau-K18, is known to undergo a disorder to order transition in the presence of lipid micelles and vesicles, in which helices form in each of the repeat domains. Here, the mechanism of helical structure formation, induced by a phospholipid mimetic, sodium dodecyl sulfate (SDS) at sub-micellar concentrations, has been studied using multiple biophysical probes. A study of the conformational dynamics of the disordered state, using photoinduced electron transfer coupled to fluorescence correlation spectroscopy (PET-FCS) has indicated the presence of an intermediate state, I, in equilibrium with the unfolded state, U. The cooperative binding of the ligand (L), SDS, to I has been shown to induce the formation of a compact, helical intermediate (IL₅) within the dead time (∼37 µs) of a continuous flow mixer. Quantitative analysis of the PET-FCS data and the ensemble microsecond kinetic data, suggests that the mechanism of induction of helical structure can be described by a U ↔ I ↔ IL₅ ↔ FL₅ mechanism, in which the final helical state, FL₅, forms from IL₅ with a time constant of 50–200 µs. Finally, it has been shown that the helical conformation is an aggregation-competent state that can directly form amyloid fibrils.     

Spatial organization and conformational peculiarities of the callatostatin family of neuropeptides.

The structures and conformational peculiarities of five members of the callatostatin family of neuropeptides, i.e. Leu- and Met-callatostatins, ranging in size from 8 to 16 amino acid residues have been investigated by a theoretical conformational analysis method. A comparative analysis of the conformational flexibilities of Met-callatostatin with those of the hydroxylated analogues, [Hyp2]- and [Hyp3]-Met-callatostatin has been carried out. Helically packed C-terminal pentapeptide in the structure of all investigated Leu-callatostatins are shown to be possible. The reason for the great number low-energy conformers for the callatostatin N-terminus is discussed.     

Export of proteins across membranes: The helix reversion hypothesis

A model is presented which explains the biological role of the leader peptide in protein export. Along the lines of this model, the conformational changes of a protein with environment serves as a general mechanism for translocation. The leader peptide in the cytoplasm takes a hairpin like conformation which reverts to an extended helix upon integration into the membrane. The essential features of this model are in accord with recent results of protein export.     

Periodic electric field as a biopolymer conformation switch: a possible mechanism

A theoretical model is proposed to describe the influence of a periodic electric field (PEF) upon a biopolymer. The biopolymer is treated as a classical mechanical system consisting of subsystems (molecular groups) which interact with each other through potential forces. The PEF is treated as a periodic driving force applied to a molecular group. The energy dissipation is considered using the model of fluid (viscous) friction. Arguments for the non-linear character of the friction-velocity dependence caused by the non-Newtonian rheology of a viscous medium are formulated.A forced molecular-group motion is investigated for the situation of a small driving-force period, with oscillations overdamped and a driving force consisting of more than one harmonic. As a result, it is established that the motion always gets to a terminal stage when only a small-scale vibration about some point, X ^*, takes place. The terminal motion is preceded by a transient characterized by the presence of a directional velocity component and so by a drift along a potential profile. the drift goes on until a barrier is met which has a sufficiently large steepness (the barrier height is not important). As a result, the point X ^* may happen to be remote from the conformation potential local minimum (conformational state). The physical reasons for the drift are described.If we consider the small-scale vibration about X ^* in the framework of the hierarchy of scales for intramolecular mobility, it can be regarded as an equilibrium mobility, whereas the drift can be regarded as a functionally important motion, and X ^* as a new conformational state which is realizable only in the presence of the PEF. It may be concluded, as the result of a consistent treatment and neglecting the small-scale vibration, that the conformational potential is modified by adding a linear term (in the one-dimensional case). In this connection, the set of conformational states can both deform (deviation of the positions of minima and their relative depth) and rearrange qualitatively (some minima can vanish and/or new minima can appear). In particular, the transition from one conformation to another one may happen due to rearrangement.     

Diel drift of Chironomidae larvae in a pristine Idaho mountain stream

Simultaneous hourly net collections in a meadow and canyon reach of a mountain stream determined diel and spatial abundances of drifting Chironomidae larvae. Sixty-one taxa were identified to the lowest practical level, 52 in the meadow and 41 in the canyon. Orthocladiinae was the most abundant subfamily with 32 taxa and a 24 h mean density of 294 individuals 100 m⁻³ (meadow) and 26 taxa and a mean of 648 individuals 100 m⁻³ (canyon). Chironominae was the second most abundant subfamily. Nonchironomid invertebrates at both sites and total Chironomidae larvae (meadow) were predominantly night-drifting. Parakiefferiella and Psectrocladius were day-drifting (meadow) whereas 8 other chironomid taxa (meadow) and 2 taxa (canyon) were night-drifting. All others were aperiodic or too rare to test periodicity, Stempellinella cf brevis Edwards exhibited catastrophic drift in the canyon only. The different drift patterns between sites is attributed to greater loss of streambed habitat in the canyon compared to the meadow as streamflow decreased. Consequent crowding of chironomid larvae in the canyon caused catastrophic drift or interfered with drift periodicty. This study adds to knowledge of Chironomidae drift and shows influences on drift of hydrologic and geomorphic conditions.     

Comparison of the predicted structure for the activated form of the P21 protein with the X-ray crystal structure

The predicted conformation and position of the central transforming region (residues 55–67) of the p21 protein are compared with the conformation and position of this segment in a recently determined X-ray crystal structure of residues 1–166 of this protein in the activated state bound to a nonhydrolyzable GTP derivative. We previously predicted that this segment of the protein would adopt a roughly extended conformation from Ile 55-Thr 58, a reverse turn at Ala 59-Gln 61, followed by an -helix from Glu 62-Met 67. We further predicted that this region of the activated protein occupies a position that is virtually identical to corresponding regions in the homologous purine nucleotide-binding proteins, bacterial elongation factor (EF-tu), and adenylate kinase (ADK). We find that there is a close correspondence between the conformation and position of our predicted structure and those found in the X-ray crystal structure. A mechanism for activation of the protein is proposed and is corroborated by X-ray crystallographic data.     

Effects of water level fluctuation on the growth ofNelumbo nucifera Gaertn. in Lake Kasumigaura,Japan

Investigations were made of the growth ofNelumbo nucifera, an aquatic higher plant, in a natural stand in Lake Kasumigaura. A rise of 1.0 m in the water level after a typhoon in August 1986 caused a subsequent decrease in biomass ofN. nucifera from the maximum of 291 g d.w. m⁻² in July to a minimum of 75 g d.w. m⁻². The biomass recovered thereafter in shallower regions. The underground biomass in October tended to increase toward the shore. The total leaf area index (LAI) is the sum of LAI of floating leaves and emergent leaves. The maximum total LAI was 1.3 and 2.8 m² m⁻² in 1986 and 1987, respectively. LAI of floating leaves did not exceed 1 m² m⁻². The elongation rates of the petiole of floating and emergent leaves just after unrolling were 2.6 and 3.4 cm day⁻¹, respectively. The sudden rise in water level (25 cm day⁻¹) after the typhoon in August 1986 caused drowning and subsequent decomposition of the mature leaves. Only the young leaves were able to elongate, allowing their laminae to reach the water surface. The fluctuation in water level, characterized by the amplitude and duration of flooding and the time of flooding in the life cycle, is an important factor determining the growth and survival ofN. nucifera in Lake Kasumigaura.     

Prediction of the secondary structures of bovine blood coagulation factor IX, factor X, and prothrombin

The secondary structures of bovine blood coagulation factors IX and X, as well as that of bovine prothrombin, were predicted on the basis of a computerized combination of the Chou-Fasman and Burgess algorithms. Refinements in the predictions were made after consideration of the content of various secondary structures, as determined by circular dichroism studies of these same proteins. The final turn assignments were in good agreement with those assigned with use of an algorithm involving pattern matching of -turns in proteins of known structure.