Nitration and oligomerization of tau induced by peroxynitrite inhibit its microtubule-binding activity

Abnormally nitrated tau has been found recently in the neurofibrillary tangles of Alzheimer's disease (AD). However, whether and how nitration of tau is involved in AD pathology is not known. Herein, we found that in vitro incubation of peroxynitrite with recombinant tau resulted in nitration and oligomerization of tau in a dosage-dependent manner. Moreover, the nitrated tau showed a significantly decreased binding activity to taxol-stabilized microtubulesin in vitro. Further study demonstrated that peroxynitrite also induced tau nitration in neuroblastoma N2a cell line, and the nitrated tau was accumulated in the cells. We conclude that abnormal nitration of tau contributes to the impaired biological activity of tau in binding to the microtubules and the aggregation of tau, implying a novel mechanism responsible for the neurodegeneration seen in AD brain.     

Accelerated evolution of the pituitary adenylate cyclase-activating polypeptide precursor gene during human origin

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide abundantly expressed in the central nervous system and involved in regulating neurogenesis and neuronal signal transduction. The amino acid sequence of PACAP is extremely conserved across vertebrate species, indicating a strong functional constraint during the course of evolution. However, through comparative sequence analysis, we demonstrated that the PACAP precursor gene underwent an accelerated evolution in the human lineage since the divergence from chimpanzees, and the amino acid substitution rate in humans is at least seven times faster than that in other mammal species resulting from strong Darwinian positive selection. Eleven human-specific amino acid changes were identified in the PACAP precursors, which are conserved from murine to African apes. Protein structural analysis suggested that a putative novel neuropeptide might have originated during human evolution and functioned in the human brain. Our data suggested that the PACAP precursor gene underwent adaptive changes during human origin and may have contributed to the formation of human cognition.     

Crystal structure of Methanococcus voltae RadA in complex with ADP: hydrolysis-induced conformational change

Members of a superfamily of RecA-like recombinases facilitate a central strand exchange reaction in the DNA repair process. Archaeal RadA and Rad51 and eukaryal Rad51 and meiosis-specific DMC1 form a closely related group of recombinases distinct from bacterial RecA. Nevertheless, all such recombinases share a conserved core domain which carries the ATPase site and putative DNA-binding sites. Here we present the crystal structure of an archaeal RadA from Methanococcus voltae (MvRadA) in complex with ADP and Mg2+ at 2.1 A resolution. The crystallized RadA-ADP filament has an extended helical pitch similar to those of previously determined structures in the presence of nonhydrolyzable ATP analogue AMP-PNP. Structural comparison reveals two recurrent conformations with an extensive allosteric effect spanning the ATPase site and the putative DNA-binding L2 region. Varied conformations of the L2 region also imply a dynamic nature of recombinase-bound DNA.     

Ex vivo characterization of the autoimmune T cell response in the HLA-DR1 mouse model of collagen-induced arthritis reveals long-term activation of type II collagen-specific cells and their presence in arthritic joints

Although the pathogenesis of collagen-induced arthritis (CIA), a model of rheumatoid arthritis, is mediated by both collagen-specific CD4(+) T cells and Ab specific for type II collagen (CII), the role of CII-specific T cells in the pathogenesis of CIA remains unclear. Using tetrameric HLA-DR1 with a covalently bound immunodominant CII peptide, CII(259-273), we studied the development of the CII-specific T cell response in the periphery and arthritic joints of DR1 transgenic mice. Although the maximum number of DR1-CII-tetramer(+) cells was detected in draining lymph nodes 10 days postimmunization, these T cells accounted for only 1% or less of the CD4(+) population. After day 10, their numbers gradually decreased, but were still detectable on day 130. Examination of TCR expression and changes in CD62L, CD44(high), and CD69 expression by these T cells indicated that they expressed a limited TCR-BV repertoire and had clearly undergone activation. RT-PCR analysis of cytokine expression by the tetramer(+) T cells compared with tetramer(-) cells indicated the tetramer(+) cells expressed high levels of Th1 and proinflammatory cytokines, including IL-2, IFN-gamma, IL-6, TNF-alpha, and especially IL-17. Additionally, analysis of the synovium from arthritic paws indicated that the same CD4(+)/BV8(+)/BV14(+)/tetramer(+) T cells were present in the arthritic joints. These data demonstrate that although only small numbers of CII-specific T cells are generated during the development of CIA, these cells express very high levels of cytokine mRNA and appear to preferentially migrate to the arthritic joint, indicating a potential direct role of CII-specific T cells in the pathogenesis of CIA.     

Novel synthetic jasmonates as highly efficient elicitors for taxoid production by suspension cultures of Taxus chinensis

Suspension cultures of Taxus chinensis were used as a model plant cell system to evaluate novel synthetic jasmonates as elicitors for stimulating the biosynthesis of secondary metabolites. Significant increases in accumulation of taxuyunnanine C (Tc) were observed in the presence of newly synthesized 2-hydroxyethyl jasmonate (HEJA) and trifluoroethyl jasmonate (TFEJA) without their inhibition on cell growth. Addition of 100 microM HEJA or TFEJA on day 7 led to a high Tc content of 44.3 +/- 1.1mg/g or 39.7 +/- 1.1 mg/g (at day 21), while the Tc content was 14.0 +/- 0.1 mg/g and 32.4 +/- 1.6 mg/g for the control and that with addition of 100 microM methyl jasmonate (MJA), respectively. The superior stimulating ability of HEJA and TFEJA over MJA, which was generally considered as the best chemical for eliciting taxoid biosynthesis, suggests that the novel jasmonate analogues may have great potential in application to other cell culture systems for effcient elicitation of plant secondary metabolites.