泛肽系统的组成和功能(二)——生物学功能及在生物技术中的应用前景

本文讨论了泛肽系统的生物学功能及其在生物技术中的应用前景。介绍了泛肽系统参与调节的多种生理和发育过程     

Novel human mPGES-1 inhibitors identified through structure-based virtual screening

Microsomal prostaglandin E synthase-1 (mPGES-1) is an inducible prostaglandin E synthase after exposure to pro-inflammatory stimuli and, therefore, represents a novel target for therapeutic treatment of acute and chronic inflammatory disorders. It is essential to identify mPGES-1 inhibitors with novel scaffolds as new leads or hits for the purpose of drug design and discovery that aim to develop the next-generation anti-inflammatory drugs. Herein we report novel mPGES-1 inhibitors identified through a combination of large-scale structure-based virtual screening, flexible docking, molecular dynamics simulations, binding free energy calculations, and in vitro assays on the actual inhibitory activity of the computationally selected compounds. The computational studies are based on our recently developed three-dimensional (3D) structural model of mPGES-1 in its open state. The combined computational and experimental studies have led to identification of new mPGES-1 inhibitors with new scaffolds. In particular, (Z)-5-benzylidene-2-iminothiazolidin-4-one is a promising novel scaffold for the further rational design and discovery of new mPGES-1 inhibitors. To our best knowledge, this is the first time a 3D structural model of the open state mPGES-1 is used in structure-based virtual screening of a large library of available compounds for the mPGES-1 inhibitor identification. The positive experimental results suggest that our recently modeled trimeric structure of mPGES-1 in its open state is ready for the structure-based drug design and discovery.     

The rice tapetum-specific gene RA39 encodes a type I ribosome-inactivating protein

A tapetum-specific cDNA encoded by a rice gene, RA39, was isolated by cDNA subtractive hybridization, differential screening and rapid amplification of cDNA ends. RA39 is a single-copy gene in the rice genome. mRNA in situ hybridization indicates that this gene is a tapetum-specific gene, and highly expressed in the tapetal cells at the meiosis and tetrad stages. The RA39 cDNA is 1,013 bp in length with an open reading frame encoding 298 amino acid residues. This cDNA sequence does not show significant homology to any known sequences in GenBank databases, but its deduced amino acid sequence (RA39) has between 19 and 34% sequence identity to ribosome-inactivating proteins (RIPs). Optimal alignment reveals that the five amino acid residues constituting the active site of the ricin A-chain (Tyr⁸⁰, Tyr¹²³, Glu¹⁷⁷, Arg¹⁸⁰ and Trp²¹¹), which are invariant among all RIPs published to date, are conserved in RA39. Recombinant RA39 protein expressed in Escherichia coli was purified to homogeneity. The purified protein exhibits the RNA N-glycosidase activity of RIPs. This demonstrates that RIPs occur in the reproductive organs of rice. The possible function of RA39 in anther development is discussed.     

Regulation of synthesis and activity of NAD(+)-dependent 15-hydroxy-prostaglandin dehydrogenase (15-PGDH) by dexamethasone and phorbol ester in human erythroleukemia (HEL) cells

Dexamethasone stimulated 15-PGDH activity in HEL cells in a time and concentration dependent manner. Increase in 15-PGDH activity by dexamethasone was found to be accompanied by an increase in enzyme synthesis as revealed by Western blot and [35S]methionine labeling studies. In addition to dexamethasone, other anti-inflammatory steroids also increased 15-PGDH activity in the order of their glucocorticoid activity. Among sex steroids only progesterone increased significantly 15-PGDH activity. 12-0-Tetradecanoylphorbol-13-acetate (TPA) also induced the synthesis of 15-PGDH but inhibited the enzyme activity. It appears that TPA caused a time dependent inactivation of 15-PGDH by a protein kinase C mediated mechanism.     

The structure of SecB/OmpA as visualized by electron microscopy: The mature region of the precursor protein binds asymmetrically to SecB

SecB, a molecular chaperone in Escherichia coli, binds a subset of precursor proteins that are exported across the plasma membrane via the Sec pathway. Previous studies showed that SecB bound directly to the mature region rather than to the signal sequence of the precursor protein. To determine the binding pattern of SecB and the mature region of the preprotein, here, we visualized the structure of the SecB/OmpA complex by electron microscopy. This complex is composed by two parts: the main density represents one SecB tetramer and the unfolded part of OmpA wrapping round it; the elongated smaller density represents the rest of OmpA. Each SecB protomer makes a different contribution to the binding of SecB with OmpA. The binding pattern between SecB tetramer and OmpA is asymmetric.     

Axonal and presynaptic RNAs are locally transcribed in glial cells.

In the last few years, the long-standing opinion that axonal and presynaptic proteins are exclusively derived from the neuron cell body has been substantially modified by the demonstration that active systems of protein synthesis are present in axons and nerve terminals. These observations have raised the issue of the cellular origin of the involved RNAs, which has been generally attributed to the neuron soma. However, data gathered in a number of model systems indicated that axonal RNAs are synthesized in the surrounding glial cells. More recent experiments on the perfused squid giant axon have definitively proved that axoplasmic RNAs are transcribed in periaxonal glia. Their delivery to the axon occurs by a modulatory mechanism based on the release of neurotransmitters from the stimulated axon and on their binding to glial receptors. In additional experiments on squid optic lobe synaptosomes, presynaptic RNA has been also shown to be synthesized locally, presumably in nearby glia. Together with a wealth of literature data, these observations indicate that axons and nerve terminals are endowed with a local system of gene expression that supports the maintenance and plasticity of these neuronal domains.