The archaeal triphosphate tunnel metalloenzyme SaTTM defines structural determinants for the diverse activities in the CYTH protein family

CYTH proteins make up a large superfamily that is conserved in all three domains of life. These enzymes have a triphosphate tunnel metalloenzyme (TTM) fold, which typically results in phosphatase functions, e.g., RNA triphosphatase, inorganic polyphosphatase, or thiamine triphosphatase. Some CYTH orthologs cyclize nucleotide triphosphates to 3′,5′-cyclic nucleotides. So far, archaeal CYTH proteins have been annotated as adenylyl cyclases, although experimental evidence to support these annotations is lacking. To address this gap, we characterized a CYTH ortholog, SaTTM, from the crenarchaeote Sulfolobus acidocaldarius. Our in silico studies derived ten major subclasses within the CYTH family implying a close relationship between these archaeal CYTH enzymes and class IV adenylyl cyclases. However, initial biochemical characterization reveals inability of SaTTM to produce any cyclic nucleotides. Instead, our structural and functional analyses show a classical TTM behavior, i.e., triphosphatase activity, where pyrophosphate causes product inhibition. The Ca²⁺-inhibited Michaelis complex indicates a two-metal-ion reaction mechanism analogous to other TTMs. Cocrystal structures of SaTTM further reveal conformational dynamics in SaTTM that suggest feedback inhibition in TTMs due to tunnel closure in the product state. These structural insights combined with further sequence similarity network–based in silico analyses provide a firm molecular basis for distinguishing CYTH orthologs with phosphatase activities from class IV adenylyl cyclases.     

Work that body: fin and body movements determine herbivore feeding performance within the natural reef environment

Herbivorous fishes form a keystone component of reef ecosystems, yet the functional mechanisms underlying their feeding performance are poorly understood. In water, gravity is counter-balanced by buoyancy, hence fish are recoiled backwards after every bite they take from the substrate. To overcome this recoil and maintain contact with the algae covered substrate, fish need to generate thrust while feeding. However, the locomotory performance of reef herbivores in the context of feeding has hitherto been ignored. We used a three-dimensional high-speed video system to track mouth and body kinematics during in situ feeding strikes of fishes in the genus Zebrasoma, while synchronously recording the forces exerted on the substrate. These herbivores committed stereotypic and coordinated body and fin movements when feeding off the substrate and these movements determined algal biomass removed. Specifically, the speed of rapidly backing away from the substrate was associated with the magnitude of the pull force and the biomass of algae removed from the substrate per feeding bout. Our new framework for measuring biting performance in situ demonstrates that coordinated movements of the body and fins play a crucial role in herbivore foraging performance and may explain major axes of body and fin shape diversification across reef herbivore guilds.     

Numerical Cognition: Reading Numbers from the Brain

How the human brain encodes numbers is revealed by a new analysis of patterns of brain activity. The findings address the nature of numerical representations and homology between humans and non-human primates.     

Force of knee extensor and flexor muscles and cross-sectional area determined by nuclear magnetic resonance imaging

The maximal strengths of knee extensor (E) and flexor (F) muscles were compared in a group of 6 male subjects aged 24-31 years. Cross-sectional area (CSA) of E and F was evaluated from planimetric measurements of Nuclear Magnetic Resonance (NMR) imaging axial scans, carried out at five levels along the thigh. Maximal CSA for E was found at 2/3 upper femur height and at 1/3 lower femur height for F. Maximum isometric force (MIF) of E was found to be 135% greater than that of F. The maximum CSA of E was found to be 93% larger than CSA of F. The calculated mechanical advantage of the flexors was estimated to be 13.8% higher than that of the knee extensors (0.116 +/- 0.012 and 0.132 +/- 0.005, respectively). However, when MIF of E and F were standardised for their respective CSA, no significant difference was found between their stress: 80.1 +/- 15.5 N.cm-2 for E and 70.5 +/- 7.0 N.cm-2 for F. From the present study, it is concluded that no significant difference exists between the maximum stress of knee extensor and flexor muscles despite large differences in their absolute values of force and CSA and that the NMR imaging technique enables accurate in-vivo determination of the CSA of individual muscles.     

Effects of peptides and steroid hormones on cell kinetic parameters of normal human breast tissue in organ culture

Summary Several studies have shown the importance of different hormones in the regulation of mammary tsssue growth. The use of organ culture techniques has shown tremendous value for the knowledge of cell proliferation in human breast tissue. Therefore, the purpose of these studies was to analyze the length of the cell cycle, DNA-labeling index, mitotic index, and growth fraction under the effects of insulin, hydrocortisone, and 17-β estradiol in 5-d organ culture. Normal tissues obtained from patients who underwent breast surgery for benign lesions were individually cultured at 37°C (95% air:5% CO₂ in Medium 199). Autoradiographic studies indicated that the hormones shortened the length of cell cycle of normal breast tissue in 5-d organ cultures. From the growth fraction studies we concluded that the hormones may have stimulated the cells to reenter the cell cycle from G₀ because these values were increased by the hormones used. Estrogen can alter the S phase duration with a consequent increase in the rate of DNA synthesis which may explain the high DNA-labeling index observed in the present studies. Supported by Public Health Service grant CA38921 from the National Cancer Institute, Bethesda, MD, and by an Institutional grant from the United Foundation of Greater Detroit.     

Syngeneic leukemia models using lentiviral transgenics

Animal models are necessary to study cancer and develop treatments. After decades of intensive research, effective treatments are available for only a few types of leukemia, while others are currently incurable. Our goal was to generate novel leukemia models in immunocompetent mice. We had achieved abilities for overexpression of multiple driving oncogenes simultaneously in normal primary cells, which can be transplanted and followed in vivo. Our experiments demonstrated the induction of primary malignant growth. Leukemia lines that model various types of leukemia, such as acute myeloid leukemia (AML) or chronic lymphocytic leukemia (CLL), were passaged robustly in congenic wild-type immunocompetent mice. These novel leukemia lines, which may complement previous models, offer the flexibility to generate tailored models of defined oncogenes of interest. The characterization of our leukemia models in immunocompetent animals can uncover the mechanisms of malignancy progression and offer a unique opportunity to stringently test anti-cancer chemotherapies.Subject terms: Cancer models, Haematopoietic stem cells, Leukaemia     

Apoptotic cells represent a dynamic stem cell niche governing proliferation and tissue regeneration

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