Transcriptomic responses to low temperature stress in the Nile tilapia, Oreochromis niloticus.

The Nile tilapia, Oreochromis niloticus, is a species of high economic value and extensively cultured. The limited stress tolerance of this species to a low temperature usually leads to mass mortality and great loss. Nevertheless, there is limited information on the molecular mechanisms underlying the susceptibility to low temperature in the tilapia. In this study, tilapia was treated at 28 °C to a lethal temperature of 8 °C by a gradual decrement. Transcriptomic response of the immune organ, kidney, in tilapia was characterized using RNA-seq. In total, 2191 genes were annotated for significant expression, which were mainly associated with metabolism and immunity. Pathway analysis showed that immune-related pathways of phagosome and cell adhesion molecules (CAMs) pathway were significantly down-regulated under low temperature. Moreover, ferroptosis, a significantly changed pathway involved in tissue damage and acute renal failure, is reported here for the first time. The levels of serum parameters associated with kidney damage such as urea and uric acid (UA) increased significantly under low temperature. The immunofluorescence staining of the kidney showed that cell apoptosis occurred at low temperature. The results of the present study indicate that exposure to low temperature can cause kidney disfunction and down-regulate the immune-related pathway in the kidney of tilapia. This study provides new insight into the mechanism of kidney damage in fish under low temperature.

Solution structure, dynamics and binding studies of a family 11 carbohydrate-binding module from Clostridium thermocellum (CtCBM11).

Non-catalytic cellulosomal CBMs (carbohydrate-binding modules) are responsible for increasing the catalytic efficiency of cellulosic enzymes by selectively putting the substrate (a wide range of poly- and oligo-saccharides) and enzyme into close contact. In the present study we carried out an atomistic rationalization of the molecular determinants of ligand specificity for a family 11 CBM from thermophilic Clostridium thermocellum [CtCBM11 (C. thermocellum CBM11)], based on a NMR and molecular modelling approach. We have determined the NMR solution structure of CtCBM11 at 25°C and 50°C and derived information on the residues of the protein that are involved in ligand recognition and on the influence of the length of the saccharide chain on binding. We obtained models of the CtCBM11-cellohexaose and CtCBM11-cellotetraose complexes by docking in accordance with the NMR experimental data. Specific ligand-protein CH-π and Van der Waals interactions were found to be determinant for the stability of the complexes and for defining specificity. Using the order parameters derived from backbone dynamics analysis in the presence and absence of ligand and at 25°C and 50°C, we determined that the protein's backbone conformational entropy is slightly positive. This data in combination with the negative binding entropy calculated from ITC (isothermal titration calorimetry) studies supports a selection mechanism where a rigid protein selects a defined oligosaccharide conformation.