Calcium binding mode of gamma-carboxyglutamic acids in conantokins.

Conantokin-T (con-T) and conantokin-G (con-G) are two highly homologous peptide toxins found in Conus venom. The former is a 21-residue peptide with four gamma-carboxyglutamic acid (Gla) residues (at positions 3, 4, 10 and 14), while the latter is a 17-residue peptide with five gamma-carboxyglutamic acid residues (at positions 3, 4, 7, 10 and 14). Despite the apparent similarity in number and relative positions of the gamma-carboxyglutamic acid residues, (113)Cd-NMR studies indicated a distinct metal binding behavior for con-G and con-T. There appears to be four binding sites in con-G in contrast to one metal binding site in con-T. To elucidate the mode of calcium binding by the gamma-carboxyglutamic acid residues in these conantokins, we designed various analogous peptides with their gamma-carboxyglutamic acid replaced by other amino acid residues. (113)Cd-NMR experiments on conantokin analogues reveal that the major difference in the number of metal binding sites between con-G and con-T is due to the residue at position 7. We also performed molecular simulations to calculate the relative binding free energies of several potential binding sites. Based on our theoretical and experimental results, we propose a 'four-site' binding model for conantokin-G and a 'single-site' binding model for conantokin-T.     

DETERMINATION OF GUSTATORY SUCROSE THRESHOLD IN WATER BY USE OF A LINEAR SUCROSE GRADIENT

A novel experimental method was developed which allows the determination of the threshold concentration of sucrose by use of a linear sucrose gradient in water. With this method a continuous tasting of the test-liquid is possible. A panel of 15 persons experienced in taste-testing was used. Three gradients of different steepness were applied: 0 to 1.5% (w/w) sucrose in 2 min (I), 3 min (II) and 4 min (III). The results of the new method were compared with those of the standard method (DIN). With gradients I and II we found values which were significantly higher than those of the standard method (I: 0.49% (w/w); II: 0.46% (w/w); DIN: 0.31% (w/w)), whereas with gradient III the same threshold value was found as with the DIN-Method (III: 0.32% (w/w)).     

Cytoplasmic filaments and cellular wound healing in amoeba proteus

The flexibility and self-healing properties of animal cell surface membranes are well known. These properties have been best exploited in various micrurgical studies on living cells (2, 3), especially in amoebae (7, 20). During nuclear transplantation in amoebae, the hole in the membrane through which a nucleus passes can have a diameter of 20-30 μm, and yet such holes are quickly sealed, although some cytoplasm usually escapes during the transfer. While enucleating amoebae in previous studies, we found that if a very small portion of a nucleus was pushed through the membrane and exposed to the external medium, the amoeba expelled such a nucleus on its own accord. When this happened, a new membrane appeared to form around the embedded portion of the nucleus and no visible loss of cytoplasm occurred during nuclear extrusion. In the present study, we examined amoebae that were at different stages of expelling partially exposed nuclei, to follow the sequence of events during the apparent new membrane formation. Unexpectedly, we found that a new membrane is not formed around the nucleus from inside but a hole is sealed primarily by a constriction of the existing membrane, and that cytoplasmic filaments are responsible for the prevention of the loss of cytoplasm.     

Characterization and structural analyses of nonspecific lipid transfer protein 1 from mung bean

Plant nonspecific lipid transfer proteins (nsLTPs) are thermal stable proteins that are capable of transferring lipid molecules between bilayers in vitro. This family of proteins, abundant in plants, is proposed to be involved in defense, pollination, and germination; the in vivo biological function remains, however, elusive. Here we report the purification and sequencing of an nsLTP1 from mung bean sprouts. We have also determined the solution structure of this nsLTP1, which represents the first 3D structure of the dicotyledonous nsLTP1 family. The global fold of mung bean nsLTP1 is similar to those of the monocotyledonous nsLTP1 structures and consists of four alpha-helices stabilized by four disulfide bonds. There are, however, some notable differences in the C-terminal tails and internal hydrophobic cavities. Circular dichroism and fluorescence spectroscopy were used to compare the thermodynamics and lipid transfer properties of mung bean nsLTP1 with those of rice nsLTP1. Docking of a lipid molecule into the solution structure of mung bean nsLTP1 reveals similar binding cavities and hydrophobic interactions as in rice nsLTP1, consistent with their comparable lipid transfer properties measured experimentally.     

Quorum Sensing Is a Language of Chemical Signals and Plays an Ecological Role in Algal-Bacterial Interactions

Algae are ubiquitous in the marine environment, and the ways in which they interact with bacteria are of particular interest in the field of marine ecology. The interactions between primary producers and bacteria impact the physiology of both partners, alter the chemistry of their environment, and shape microbial diversity. Although algal-bacterial interactions are well known and studied, information regarding the chemical-ecological role of this relationship remains limited, particularly with respect to quorum sensing (QS), which is a system of stimuli and response correlated to population density. In the microbial biosphere, QS is pivotal in driving community structure and regulating behavioral ecology, including biofilm formation, virulence, antibiotic resistance, swarming motility, and secondary metabolite production. Many marine habitats, such as the phycosphere, harbor diverse populations of microorganisms and various signal languages (such as QS-based autoinducers). QS-mediated interactions widely influence algal-bacterial symbiotic relationships, which in turn determine community organization, population structure, and ecosystem functioning. Understanding infochemicals-mediated ecological processes may shed light on the symbiotic interactions between algae host and associated microbes. In this review, we summarize current achievements about how QS modulates microbial behavior, affects symbiotic relationships, and regulates phytoplankton chemical-ecological processes. Additionally, we present an overview of QS-modulated co-evolutionary relationships between algae and bacterioplankton, and consider the potential applications and future perspectives of QS.     

Genistein inhibits calcium release by platelet-derived growth factor but not bradykinin or cadmium in human fibroblasts

Cd²⁺ provokes inositol trisphosphateproduction and releases stored Ca²⁺, apparently by binding to a zinc site in the external domain of an orphan receptor. One pM Cd²⁺ evokes an immediate spike in cytosolic free Ca²⁺, which is similar to that evoked by bradykinin. Platelet-derived growth factor (PDGF) also increases free Ca²⁺ in human dermalfibroblasts, but there is a distinct lag before free Ca²⁺ rises in response to PDGF. Genistein, which selectively inhibits tyrosine kinases, markedly inhibited Ca²⁺ mobilization evoked by PDGF. Calcium mobilization triggered by cadmium or bradykinin was relatively insensitive to genistein. The PDGF receptor is known to be a tyrosine kinase, whichphosphorylates and thereby activatesphospholipase C, whereas a G protein couples the bradykinin receptor to anotherphospholipase C isoform. These findings support the hypothesis that the orphan receptor triggered by cadmium is coupled to phospholipase C via a G protein.Abbreviations BSA bovine serum albumin - BK bradykinin - [Ca²⁺]_i cytosolic free calcium - DME Dulbecco's modified Eagle's medium - FBS fetal bovine serum - HEPES 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid - IC₅₀ concentration that produces 50% inhibition - PDGF platelet-derived growth factor - PSS physiological salts solution - SE standard error of the mean     

Leaf size of woody dicots predicts ecosystem primary productivity

A key challenge in ecology is to understand the relationships between organismal traits and ecosystem processes. Here, with a novel dataset of leaf length and width for 10 480 woody dicots in China and 2374 in North America, we show that the variation in community mean leaf size is highly correlated with the variation in climate and ecosystem primary productivity, independent of plant life form. These relationships likely reflect how natural selection modifies leaf size across varying climates in conjunction with how climate influences canopy total leaf area. We find that the leaf size?primary productivity functions based on the Chinese dataset can predict productivity in North America and vice‐versa. In addition to advancing understanding of the relationship between a climate‐driven trait and ecosystem functioning, our findings suggest that leaf size can also be a promising tool in palaeoecology for scaling from fossil leaves to palaeo‐primary productivity of woody ecosystems.