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851.
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Ha JH Karchin JM Walker-Kopp N Huang LS Berry EA Loh SN 《Journal of molecular biology》2012,416(4):495-502
Domain swapping is a mechanism for forming protein dimers and oligomers with high specificity. It is distinct from other forms of oligomerization in that the binding interface is formed by reciprocal exchange of polypeptide segments. Swapping plays a physiological role in protein–protein recognition, and it can also potentially be exploited as a mechanism for controlled self-assembly. Here, we demonstrate that domain-swapped interfaces can be engineered by inserting one protein into a surface loop of another protein. The key to facilitating a domain swap is to destabilize the protein when it is monomeric but not when it is oligomeric. We achieve this condition by employing the “mutually exclusive folding” design to apply conformational stress to the monomeric state. Ubiquitin (Ub) is inserted into one of six surface loops of barnase (Bn). The 38-Å amino-to-carboxy-terminal distance of Ub stresses the Bn monomer, causing it to split at the point of insertion. The 2.2-Å X-ray structure of one insertion variant reveals that strain is relieved by intermolecular folding with an identically unfolded Bn domain, resulting in a domain-swapped polymer. All six constructs oligomerize, suggesting that inserting Ub into each surface loop of Bn results in a similar domain-swapping event. Binding affinity can be tuned by varying the length of the peptide linkers used to join the two proteins, which modulates the extent of stress. Engineered, swapped proteins have the potential to be used to fabricate “smart” biomaterials, or as binding modules from which to assemble heterologous, multi-subunit protein complexes. 相似文献
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This study aimed to evaluate the effect of hyperinsulinemia on hypertriglyceridemia-induced pressor response in normal and fructose-induced insulin resistant rats. The rats were divided into six groups of eight rats and were fed a fructose-enriched diet (FINs, F(INS+TG)) or a regular chow diet (C, C(TG), C(INS), C(INS+TG)) for 8 wks. The acute experiment was conducted at the end of wk 8 and consisted of a 30-min basal period and followed by a 120-min test period. After the basal period, somatostatin (1.3 microg/kg/ min) combined with regular insulin (0.6 or 4 mU/kg/min) and variable glucose infusion were given to clamp euglycemia and euinsulinemia in C and C(TG) or euglycemia and hyperinsulinemia in CINs, C(INS+TG), F(INS) and F(INS+TG). During test period, lipofundin (a triglyceride emulsion) was infused into CTG, C(INS+TG), F(INS+TG) and saline instead was infused into C, C(INS), FINS. Plasma insulin and triglyceride levels were significantly higher in fructose-fed rats than in normal rats. During the test period, the lipofundin infusion (1.2 ml/kg/hr) increased plasma triglyceride levels by 368 +/- 39, 351 +/- 71 and 489 +/- 38 mg/dl compared with their baseline levels in lipid-infused groups. During the test period, low-dose insulin infusion kept plasma insulin at basal levels in C and C(TG) and high-dose insulin infusion increased plasma insulin levels about 6 times the baseline insulin level in C. Glucose infusion rate (GIR) was significantly higher in rats with high insulin infusion than those with low insulin infusion. The increase in GIR was lower in fructose-fed groups than in control groups under similar hyperinsulinemia. Rats with or without lipofundin infusion did not alter GIR during the test period. The present results demonstrated that hypertriglyceridemia-induced pressor response was diminished under hyperinsulinemic condition in both normal and fructose-induced insulin resistant rats. 相似文献
856.
Wuelton M Monteiro Fernando FA Val André M Siqueira Gabriel P Franca Vanderson S Sampaio Gisely C Melo Anne CG Almeida Marcelo AM Brito Henry M Peixoto Douglas Fuller Quique Bassat Gustavo AS Romero Oliveira Maria Regina F Lacerda Marcus Vinícius G 《Memórias do Instituto Oswaldo Cruz》2014,109(5):553-568
857.
Symbiont‐bearing and non‐symbiotic marine bivalves were used as model organisms to establish biosignatures for the detection of distinctive symbioses in ancient bivalves. For this purpose, the isotopic composition of lipids (δ13C) and bulk organic shell matrix (δ13C, δ34S, δ15N) from shells of several thiotrophic, phototrophic, or non‐symbiotic bivalves were compared (phototrophic: Fragum fragum, Fragum unedo, Tridacna maxima; thiotrophic: Codakia tigerina, Fimbria fimbriata, Anodontia sp.; non‐symbiotic: Tapes dorsatus, Vasticardium vertebratum, Scutarcopagia sp.). ?13C values of bulk organic shell matrices, most likely representing mainly original shell protein/chitin biomass, were depleted in thio‐ and phototrophic bivalves compared to non‐symbiotic bivalves. As the bulk organic shell matrix also showed a major depletion of δ15N (down to –2.2 ‰) for thiotrophic bivalves, combined δ13C and δ15N values are useful to differentiate between thio‐, phototrophic, and non‐symbiotic lifestyles. However, the use of these isotopic signatures for the study of ancient bivalves is limited by the preservation of the bulk organic shell matrix in fossils. Substantial alteration was clearly shown by detailed microscopic analyses of fossil (late Pleistocene) T. maxima and Trachycardium lacunosum shell, demonstrating a severe loss of quantity and quality of bulk organic shell matrix with time. Likewise, the composition and δ13C‐values of lipids from empty shells indicated that a large part of these compounds derived from prokaryotic decomposers. The use of lipids from ancient shells for the reconstruction of the bivalve's life style therefore appears to be restricted. 相似文献
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M Verma R Metgud AS Madhusudan N Verma M Saxena A Soni 《Biotechnic & histochemistry》2014,89(7):529-534
Diabetes has been reported to affect salivary glands adversely in humans and experimental models. Glutamate oxaloacetate transaminase (GOT), glutamate pyruvate transaminase (GPT) and lactate dehydrogenase (LDH) are salivary enzymes that also are widely distributed in animal tissues. We determined GOT and GPT levels in saliva samples of 100 type 1 and 30 type 2 diabetic patients using reflectance spectrophotometry and compared them to 30 age and sex matched healthy controls. Statistically significant differences were observed in the mean values of GOT and GPT in type 1 diabetics compared to type 2 and control groups. Significantly higher GOT levels were found in the 1–20 year age group of type 1 diabetics. Our findings suggest that salivary gland damage is due to the same immunological attack that affects pancreatic β cells and results in type 1 diabetes. 相似文献