连续事件的语义数据模型

语义抽象概念aggregation和generalization不仅对不包含时间概念的复杂情况的数据模型的建立很有用，而且还可以成功地用于连续事件的建模。建立了两种情况并存的语义数据模型：or—dering(次序)和sequencing(先后顺序)，并且可以在任何程序环境下实现。     

A receptor kinase gene regulating symbiotic nodule development

Leguminous plants are able to establish a nitrogen-fixing symbiosis with soil bacteria generally known as rhizobia. Metabolites exuded by the plant root activate the production of a rhizobial signal molecule, the Nod factor, which is essential for symbiotic nodule development. This lipo-chitooligosaccharide signal is active at femtomolar concentrations, and its structure is correlated with host specificity of symbiosis, suggesting the involvement of a cognate perception system in the plant host. Here we describe the cloning of a gene from Medicago sativa that is essential for Nod-factor perception in alfalfa, and by genetic analogy, in the related legumes Medicago truncatula and Pisum sativum. The identified 'nodulation receptor kinase', NORK, is predicted to function in the Nod-factor perception/transduction system (the NORK system) that initiates a signal cascade leading to nodulation. The family of 'NORK extracellular-sequence-like' (NSL) genes is broadly distributed in the plant kingdom, although their biological function has not been previously ascribed. We suggest that during the evolution of symbiosis an ancestral NSL system was co-opted for transduction of an external ligand, the rhizobial Nod factor, leading to development of the symbiotic root nodule.     

Vaspin inhibits kallikrein 7 by serpin mechanism

The molecular target of the adipokine vaspin (visceral adipose tissue-derived serpin; serpinA12) and its mode of action are unknown. Here, we provide the vaspin crystal structure and identify human kallikrein 7 (hK7) as a first protease target of vaspin inhibited by classical serpin mechanism with high specificity in vitro. We detect vaspin–hK7 complexes in human plasma and find co-expression of both proteins in murine pancreatic β-cells. We further demonstrate that hK7 cleaves human insulin in the A- and B-chain. Vaspin treatment of isolated pancreatic islets leads to increased insulin concentration in the media upon glucose stimulation without influencing insulin secretion. By application of vaspin and generated inactive mutants, we find the significantly improved glucose tolerance in C57BL/6NTac and db/db mice treated with recombinant vaspin fully dependent on the vaspin serpin activity and not related to vaspin-mediated changes in insulin sensitivity as determined by euglycemic-hyperinsulinemic clamp studies. Improved glucose metabolism could be mediated by increased insulin plasma concentrations 150 min after a glucose challenge in db/db mice, supporting the hypothesis that vaspin may inhibit insulin degradation by hK7 in the circulation. In conclusion, we demonstrate the inhibitory serpin nature and the first protease target of the adipose tissue-derived serpin vaspin, and our findings suggest hK7 inhibition by vaspin as an underlying physiological mechanism for its compensatory actions on obesity-induced insulin resistance.     

Unidirectional molecular motor on a gold surface

Molecules capable of mimicking the function of a wide range of mechanical devices have been fabricated, with motors that can induce mechanical movement attracting particular attention. Such molecular motors convert light or chemical energy into directional rotary or linear motion, and are usually prepared and operated in solution. But if they are to be used as nanomachines that can do useful work, it seems essential to construct systems that can function on a surface, like a recently reported linear artificial muscle. Surface-mounted rotors have been realized and limited directionality in their motion predicted. Here we demonstrate that a light-driven molecular motor capable of repetitive unidirectional rotation can be mounted on the surface of gold nanoparticles. The motor design uses a chiral helical alkene with an upper half that serves as a propeller and is connected through a carbon-carbon double bond (the rotation axis) to a lower half that serves as a stator. The stator carries two thiol-functionalized 'legs', which then bind the entire motor molecule to a gold surface. NMR spectroscopy reveals that two photo-induced cis-trans isomerizations of the central double bond, each followed by a thermal helix inversion to prevent reverse rotation, induce a full and unidirectional 360 degrees rotation of the propeller with respect to the surface-mounted lower half of the system.