RESUMO
ObjectiveIt was reported that the transthyretin (TTR) has a neuroprotective effect on Alzheimer’s disease (AD), which is manifested by the ability of TTR to inhibit the pathological aggregation of amyloid beta protein (Aβ). In this work, we investigated the mechanism of the interactions between TTR and Aβ at the molecular level to reveal the neuroprotective effect of TTR on AD. MethodsProtein-protein docking was used to explore the models of interaction between different structural forms of TTR and Aβ, and molecular dynamics simulation was further applied to investigate the dynamic process of the interaction between the two. ResultsBoth TTR tetramer and monomer can interact with Aβ monomer, and the thyroxine-binding channel of TTR tetramer is the main binding site of Aβ monomer. In addition, the EF helix and EF loop of TTR tetramer were also able to bind Aβ monomer. When the TTR tetramer dissociates, the hydrophobic site of the internal TTR monomer is exposed, which has a strong affinity for Aβ monomer. For the interaction between Aβ aggregates and TTR, a higher degree of aggregation can be formed between TTR monomer and Aβ aggregates due to the β-sheet-rich property of TTR monomer and Aβ aggregates, which may therefore reduce the cytotoxicity of Aβ aggregates. ConclusionBoth TTR tetramer and monomer can inhibit Aβ aggregation by “sequestering” Aβ monomer, while TTR monomer can reduce the cytotoxicity of Aβ aggregates by forming large co-aggregation with Aβ aggregates. This work can provide an important theoretical basis for the design and discovery of anti-AD drugs based on the neuroprotective effects of TTR.
RESUMO
<p><b>OBJECTIVE</b>To study the distribution of human immunodeficiency virus (HIV)-1 genotypes in major prevalent regions of China and to illustrate the relationship between HIV-1 subtypes and mother-to-child transmission in a retrospective cohort.</p><p><b>METHODS</b>HIV-1 gag p17 and env C2-V4 region were amplified by nested-polymerase chain reaction (nPCR) and the sequences were obtained by sequencing gag nPCR products or clones of env gene.</p><p><b>RESULTS</b>60 HIV-1 positive individuals were subject to typing for gag p17 and 69 for env C2-V4 region. Single clade was only found in Henan (subtype B') and Xinjiang (subtype C), and subtypes C and E were demonstrated in Yunnan. These regions represented most of the HIV-1 infections in China. Multiple subtypes (A, B, C, E, etc.) were found in Beijing and Shanghai, where HIV infections were still in low level. The sequences of subtype C were less diversive in Xinjiang (p17: 0.0192 +/- 0.0078, C2-V4: 0.0455 +/- 0.0145) than in Yunnan (p17: 0.0279 +/- 0.0102, C2-V4: 0.0482 +/- 0.0171), but all of them clustered in "C" branch in phylogenetic trees. Trafficking of subtype C from Yunnan to Xinjiang was found but had already been reported by others. Compared to subtype C, subtype E was quite divergent (p17: 0.0473 +/- 0.0105, C2-V4: 0.1114 +/- 0.0112) in Yunnan, but no recombination was found in the C2-V4 region of env gene. Highe divergence of subtype B' was found in Henan and the peripheral provinces (p17: 0.0381 +/- 0.0101, C2-V4: 0.0691 +/- 0.0166), which might be attributed to the early epidemics of HIV-1 in these areas (early 1990's). In maternal-child cohort, subtypes B (7/21), C (11/21), E (1/21) and undefined types (2/21) were identified in non-transmitting HIV-1 positive mothers, while only subtype B (7/11) and C (4/11) appeared in transmitting HIV-1 positive mothers. The rate of transmission was 53.8% (7/13) in mothers infected with subtype B and 30.8% (4/13) in those infected with subtype C, but with no significant difference (P = 0.196). The imbalancing distribution of subtypes might be explained by the fact that transfusion or illegal blood would increased mother-to-child transmission on HIV-1 and most of mothers with clade B were infected by illegal blood transfusion in this cohort. In addition, most of the maternal-child pair's sequences clustered in gag or env phylogenetic trees but only a few did disperse among the unrelated patients because children were older (>/= 4 years).</p><p><b>CONCLUSION</b>The characteristics of HIV-1 clade's distribution differed over most parts of China but no difference was demonstrated between subtype B and C in mother-to-child transmission on HIV-1.</p>