HELIN Acquisitions Manual

HELIN Acquisitions Manual - 2007-2008 revisio

HELIN Cataloging Policies and Procedures Manual

HELIN Cataloging Manual - Nov. 2011 revisio

Effect of thiols on beta 2-adrenoceptors in human mononuclear leucocytes

The effect of the disulfide reducing agent dithiothreitol (DTT) and other thiols on binding of the beta-adrenoceptor antagonist (-)-125iodocyanopindolol (125ICYP) to human mononuclear leucocytes (MNL) was investigated. Saturation experiments and dissociation kinetics revealed two classes of specific 125ICYP binding sites, one of high and the other of low affinity, respectively. In intact MNL DTT caused a decrease in specific binding. This was due almost selectively to a decrease in the affinity of high affinity binding sites, which decreased gradually in a concentration-dependent manner to the affinity of low affinity binding sites. In MNL membranes DTT decreased not only the affinity but also the number of high affinity binding sites. The DTT effect was completely reversible by simple reoxidation on air. The structural isomers (+/-)-DTT. (-)-DTT and dithioerythritol revealed identical effects on specific binding, whereas the monothiols mercaptoethanol and alpha-monothioglycerol, having a lower redox potential, were considerably less effective. In the same concentration range that influenced specific binding. DTT stimulated intracellular cAMP production. These results suggest functionally important disulfide bridges which regulate the affinity of beta-adrenoceptor binding sites in human MNL. They stabilize the receptor in a high affinity state; their reduction causes the conversion of the high affinity state into a low affinity state in a process associated with stimulation of adenylate cyclase. Available evidence indicates that a similar transformation is made by beta-adrenoceptor agonists. Consequently low affinity 125ICYP binding sites preexistent in untreated cells could represent a reduced receptor state resulting from agonist-receptor interaction in vivo

Affinity Weighted Embedding

Supervised (linear) embedding models like Wsabie and PSI have proven successful at ranking, recommendation and annotation tasks. However, despite being scalable to large datasets they do not take full advantage of the extra data due to their linear nature, and typically underfit. We propose a new class of models which aim to provide improved performance while retaining many of the benefits of the existing class of embedding models. Our new approach works by iteratively learning a linear embedding model where the next iteration's features and labels are reweighted as a function of the previous iteration. We describe several variants of the family, and give some initial results

Thermodynamic bounds on the ultra- and infra-affinity of Hsp70 for its substrates

The 70 kDa Heat Shock Proteins Hsp70 have several essential functions in living systems, such as protecting cells against protein aggregation, assisting protein folding, remodeling protein complexes and driving the translocation into organelles. These functions require high affinity for non-specific amino-acid sequences that are ubiquitous in proteins. It has been recently shown that this high affinity, called ultra-affinity, depends on a process driven out of equilibrium by ATP hydrolysis. Here we establish the thermodynamic bounds for ultra-affinity, and further show that the same reaction scheme can in principle be used both to strengthen and to weaken affinities (leading in this case to infra-affinity). We show that cofactors are essential to achieve affinity beyond the equilibrium range. Finally, biological implications are discussed.Comment: 14 pages, 5 figure

Higher nucleoporin-Importinβ affinity at the nuclear basket increases nucleocytoplasmic import.

Several in vitro studies have shown the presence of an affinity gradient in nuclear pore complex proteins for the import receptor Importinβ, at least partially contributing to nucleocytoplasmic transport, while others have historically argued against the presence of such a gradient. Nonetheless, the existence of an affinity gradient has remained an uncharacterized contributing factor. To shed light on the affinity gradient theory and better characterize how the existence of such an affinity gradient between the nuclear pore and the import receptor may influence the nucleocytoplasmic traffic, we have developed a general-purpose agent based modeling (ABM) framework that features a new method for relating rate constants to molecular binding and unbinding probabilities, and used our ABM approach to quantify the effects of a wide range of forward and reverse nucleoporin-Importinβ affinity gradients. Our results indicate that transport through the nuclear pore complex is maximized with an effective macroscopic affinity gradient of 2000 µM, 200 µM and 10 µM in the cytoplasmic, central channel and nuclear basket respectively. The transport rate at this gradient is approximately 10% higher than the transport rate for a comparable pore lacking any affinity gradient, which has a peak transport rate when all nucleoporins have an affinity of 200 µM for Importinβ. Furthermore, this optimal ratio of affinity gradients is representative of the ratio of affinities reported for the yeast nuclear pore complex--suggesting that the affinity gradient seen in vitro is highly optimized