Structure-based thermodynamic analysis of the dissociation of protein phosphatase-1 catalytic subunit and microcystin-LR docked complexes

The relationship between the structure of a free ligand in solution and the structure of its bound form in a complex is of great importance to the understanding of the energetics and mechanism of molecular recognition and complex formation. In this study, we use a structure-based thermodynamic approach to study the dissociation of the complex between the toxin microcystin-LR (MLR) and the catalytic domain of protein phosphatase-1 (PP-1c) for which the crystal structure of the complex is known. We have calculated the thermodynamic parameters (enthalpy, entropy, heat capacity, and free energy) for the dissociation of the complex from its X-ray structure and found the calculated dissociation constant (4.0 x 10(-11)) to be in excellent agreement with the reported inhibitory constant (3.9 x 10(-11)). We have also calculated the thermodynamic parameters for the dissociation of 47 PP-1c:MLR complexes generated by docking an ensemble of NMR solution structures of MLR onto the crystal structure of PP-1c. In general, we observe that the lower the root-mean-square deviation (RMSD) of the docked complex (compared to the X-ray complex) the closer its free energy of dissociation (deltaGd(o)) is to that calculated from the X-ray complex. On the other hand, we note a significant scatter between the deltaGd(o) and the RMSD of the docked complexes. We have identified a group of seven docked complexes with deltaGd(o) values very close to the one calculated from the X-ray complex but with significantly dissimilar structures. The analysis of the corresponding enthalpy and entropy of dissociation shows a compensation effect suggesting that MLR molecules with significant structural variability can bind PP-1c and that substantial conformational flexibility in the PP-1c:MLR complex may exist in solution.     

Retention of mobile water during dehydration in the desiccation-tolerant grass Eragrostis nindensis

Leaf tensile strength was measured for the drought-tolerant grass Eragrostis curvula and the desiccation-tolerant grass E . nindensis when fully hydrated, partially dehydrated, naturally air-dried, and flash-dried. Leaf tensile strength increased in intact, air-dried leaves of E . curvula but not for similarly treated leaves of E . nindensis . Examination of leaf cross-sections by light microscopy and histochemical staining for lignins failed to show any significant structural differences between the two species in the hydrated state. When leaves were flash-dried, the tensile strength of E . curvula remained unchanged from leaves dried naturally, while there was a marked increase in the tensile strength of flash-dried leaves of E . nindensis . Proton NMR indicated that the desiccation-tolerant E . nindensis retained mobile water when leaf relative water content was less than 20% if dried naturally but not if flash-dried, whereas no mobile water was detected in leaves of E . curvula when dried either naturally or with flash-drying to below 20% relative water content. This behaviour suggests a fundamental difference in strategy for surviving water loss in vegetative tissues between desiccation-tolerant species and drought-tolerant species.     

The molecular bases of plant resistance and defense responses to aphid feeding: current status

Plant genes participating in the recognition of aphid herbivory in concert with plant genes involved in defense against herbivores mediate plant resistance to aphids. Several such genes involved in plant disease and nematode resistance have been characterized in detail, but their existence has only recently begun to be determined for arthropod resistance. Hundreds of different genes are typically involved and the disruption of plant cell wall tissues during aphid feeding has been shown to induce defense responses in Arabidopsis, Triticum, Sorghum, and Nicotiana species. Mi‐1.2, a tomato gene for resistance to the potato aphid, Macrosiphum euphorbiae (Thomas), is a member of the nucleotide‐binding site and leucine‐rich region Class II family of disease, nematode, and arthropod resistance genes. Recent studies into the differential expression of Pto‐ and Pti1‐like kinase genes in wheat plants resistant to the Russian wheat aphid, Diuraphis noxia (Mordvilko), provide evidence of the involvement of the Pto class of resistance genes in arthropod resistance. An analysis of available data suggests that aphid feeding may trigger multiple signaling pathways in plants. Early signaling includes gene‐for‐gene recognition and defense signaling in aphid‐resistant plants, and recognition of aphid‐inflicted cell damage in both resistant and susceptible plants. Furthermore, signaling is mediated by several compounds, including jasmonic acid, salicylic acid, ethylene, abscisic acid, giberellic acid, nitric oxide, and auxin. These signals lead to the development of direct chemical defenses against aphids and general stress‐related responses that are well characterized for a number of abiotic and biotic stresses. In spite of major plant taxonomic differences, similarities exist in the types of plant genes expressed in response to feeding by different species of aphids. However, numerous differences in plant signaling and defense responses unique to specific aphid–plant interactions have been identified and warrant further investigation.     

Review of records of hymenolepidids (Eucestoda: Hymenolepididae) from dormice (Rodentia: Gliridae) in Europe,with a redescription of Armadolepis spasskyi Tenora & Baruš, 1958 and the description of A. genovi n. sp.

Systematic Parasitology - Armadolepis (Armadolepis) spasskyi Tenora & Baru?, 1958 is redescribed on the basis of the type-series consisting of the holotype from the garden dormouse...     

Description of Triaenorhina burti n. sp. (Cestoda: Paruterinidae) from the Malabar trogon Harpactes fasciatus (Pennant) (Aves: Trogoniformes: Trogonidae) in Sri Lanka

Triaenorhina burti n. sp. (Cyclophyllidea: Paruterinidae) is described from Harpactes fasciatus (Trogoniformes: Trogonidae) from the Southern Province of Sri Lanka. The new species is characterised by: a body 24–32 mm long; 44 rostellar hooks alternating in two closely adjacent regular rows, with lengths of 63–65 μm (anterior row) and 39–41 μm (posterior row); regularly alternating genital pores; testes divided into two groups by the ovary and vitellarium; a gravid uterus forming a single oval sac; and a cylindrical paruterine organ not reaching the anterior proglottis margin. A key to the seven recognised species of Triaenorhina Spasskii & Shumilo, 1965 is presented.