Ion binding of cyclolinopeptide A: an NMR and CD conformational study

CD and nmr techniques have been used to study, in acetonitrile solution, the ion-complexing capability of cyclolinopeptide A (CLA), a cyclic nonapeptide of sequence cyclo-(Pro-Pro-Phe-Phe-Leu-Ile-Ile-Leu-Val) endowed with remarkable cytoprotective ability in vitro, and the conformation of the Ba(2+)/CLA complex. At room temperature, CLA in acetonitrile shows a proton nmr spectrum characteristic of the coexistence of many different conformers in intermediate exchange. The backbone contains a cis Pro-Pro bond, with all other peptide bonds in the trans conformation. CLA binds Ba2+ more tightly than the other cations studied, namely K+, Na+, Mg2+, and Ca2+; CD data are indicative of the presence of both 1:2 (sandwich) and 1:1 (equimolar) type complexes, depending on the Ba2+ ion concentration, whereas nmr data are consistent with an equimolar form. The relevant conformational features of the equimolar Ba2+/CLA complex are that the backbone contains all trans peptide bonds, a type I 6----3 beta-turn and a 3----1 gamma-turn (or a distorted 3----9 beta-turn). The global shape of the complexed peptide can be described as a bowl, with the concave (polar) side hosting Ba2+ and the convex side predominantly apolar.     

Dolphin sympatric ecology

Interspecific associations between two or more species of the family Delphinidae have been reported by many scientists, but the sympatric ecology of such dolphin associations has not been studied in great detail. A few field investigations have been conducted on this subject in different parts of the world on species such as bottlenose dolphins (Tursiops spp.), short-beaked common dolphins (Delphinus delphis), and killer whales (Orcinus orca). Sympatric dolphins seem to use different strategies to co-exist when resources appear to be limited, including dietary divergence (different prey preference, slightly diverse diet, different feeding time) and/or different habitat use (shallow versus deep waters, flat areas versus submarine canyons and escarpments, different travel routes). This paper presents a review of some well-studied dolphin species found in sympatry and discusses the nature of habitat and resource partitioning as well as studies on aggressive behaviour displayed by species living in the same habitat.     

PAC1hop receptor activation facilitates catecholamine secretion selectively through 2-APB-sensitive Ca2+ channels in PC12 cells

PACAP is a critical regulator of long-term catecholamine secretion from the adrenal medulla in vivo, however the receptor or pathways for Ca²⁺ entry triggering acute and sustained secretion have not been adequately characterized. We have previously cloned the bovine adrenal chromaffin cell PAC1 receptor that contains the molecular determinants required for PACAP-induced Ca²⁺ elevation and is responsible for imparting extracellular Ca²⁺ influx-dependent secretory competence in PC12 cells. Here, we use this cell model to gain mechanistic insights into PAC1hop-dependent Ca²⁺ pathways responsible for catecholamine secretion. PACAP-modulated extracellular Ca²⁺ entry in PC12 cells could be partially blocked with nimodipine, an inhibitor of L-type VGCCs and partially blocked by 2-APB, an inhibitor and modulator of various transient receptor potential (TRP) channels. Despite the co-existence of these two modes of Ca²⁺ entry, sustained catecholamine secretion in PC12 cells was exclusively modulated by 2-APB-sensitive Ca²⁺ channels. While IP3 generation occurred after PACAP exposure, most PACAP-induced Ca²⁺ mobilization involved release from ryanodine-gated cytosolic stores. 2-APB-sensitive Ca²⁺ influx, and subsequent catecholamine secretion was however not functionally related to intracellular Ca²⁺ mobilization and store depletion. The reconstituted PAC1hop-expessing PC12 cell model therefore recapitulates both PACAP-induced Ca²⁺ release from ER stores and extracellular Ca²⁺ entry that restores PACAP-induced secretory competence in neuroendocrine cells. We demonstrate here that although bPAC1hop receptor occupancy induces Ca²⁺ entry through two independent sources, VGCCs and 2-APB-sensitive channels, only the latter contributes importantly to sustained vesicular catecholamine release that is a fundamental characteristic of this neuropeptide system. These results emphasize the importance of establishing functional linkages between Ca²⁺ signaling pathways initiated by pleotrophic signaling molecules such as PACAP, and physiologically important downstream events, such as secretion, triggered by them.     

Gene expression regulation of adipocyte differentiation: cell cycle and hormones

The adipose conversion of cultured preadipose cells involves the activation of numerous genes and is controlled by various adipogenic and mitogenic factors. The differentiation program can be divided into early and late events. Early events are triggered by growth arrest at the G1/S boundary and characterized by the activation of a set of genes (pOb24, lipoprotein lipase, etc.). The expression of the terminal differentiation-related genes takes place after a limited growth resumption of early markers containing cells and requires the presence of permissive hormones (growth hormone and triiodothyronine). Insulin acts solely as a modulator in the expression of the terminal differentiation-related genes. In vivo studies suggest that the acquisition of new adipocytes might result from terminal differentiation of dormant, already committed (pOb24 positive) cells when exposed to appropriate mitogenic or adipogenic stimuli.