Phosphatidic acid mediates the targeting of tBid to induce lysosomal membrane permeabilization and apoptosis

Upon apoptotic stimuli, lysosomal proteases, including cathepsins and chymotrypsin, are released into cytosol due to lysosomal membrane permeabilization (LMP), where they trigger apoptosis via the lysosomal-mitochondrial pathway of apoptosis. Herein, the mechanism of LMP was investigated. We found that caspase 8-cleaved Bid (tBid) could result in LMP directly. Although Bax or Bak might modestly enhance tBid-triggered LMP, they are not necessary for LMP. To study this further, large unilamellar vesicles (LUVs), model membranes mimicking the lipid constitution of lysosomes, were used to reconstitute the membrane permeabilization process in vitro. We found that phosphatidic acid (PA), one of the major acidic phospholipids found in lysosome membrane, is essential for tBid-induced LMP. PA facilitates the insertion of tBid deeply into lipid bilayers, where it undergoes homo-oligomerization and triggers the formation of highly curved nonbilayer lipid phases. These events induce LMP via pore formation mechanisms because encapsulated fluorescein-conjugated dextran (FD)-20 was released more significantly than FD-70 or FD-250 from LUVs due to its smaller molecular size. On the basis of these data, we proposed tBid-PA interactions in the lysosomal membranes form lipidic pores and result in LMP. We further noted that chymotrypsin-cleaved Bid is more potent than tBid at binding to PA, inserting into the lipid bilayer, and promoting LMP. This amplification mechanism likely contributes to the culmination of apoptotic signaling.     

Thymine DNA glycosylase specifically recognizes 5-carboxylcytosine-modified DNA

Human thymine DNA glycosylase (hTDG) efficiently excises 5-carboxylcytosine (5caC), a key oxidation product of 5-methylcytosine in genomic DNA, in a recently discovered cytosine demethylation pathway. We present here the crystal structures of the hTDG catalytic domain in complex with duplex DNA containing either 5caC or a fluorinated analog. These structures, together with biochemical and computational analyses, reveal that 5caC is specifically recognized in the active site of hTDG, supporting the role of TDG in mammalian 5-methylcytosine demethylation.     

Chymotrypsin B cached in rat liver lysosomes and involved in apoptotic regulation through a mitochondrial pathway

Lysosomes can trigger the mitochondrial apoptotic pathway by releasing proteases. Here we report that a 25-kDa protein purified from rat liver lysosomes possesses a long standing potent Bid cleavage activity at neutral pH, and the truncated Bid can in turn induce rapid mitochondrial release of cytochrome c. This protease was revealed as chymotrypsin B by biochemical and mass spectrometric analysis. Although it was long recognized as a digestive protease exclusively secreted by the exocrine pancreas, our data support that it also expresses and intracellularly resides in rat liver lysosomes. Translocation of lysosomal chymotrypsin B into cytosol was triggered by apoptotic stimuli such as tumor necrosis factor-alpha, and intracellular delivery of chymotrypsin B protein induced apoptotic cell death with a potency comparable with cathepsin B, suggestive of a lysosomal-mitochondrial pathway to apoptosis regulated by chymotrypsin B following its release. Noteworthily, either knockdown of chymotrypsin B expression by RNA interference or pretreatment with chymotrypsin B inhibitor N-p-tosyl-L-phenylalanine chloromethyl ketone significantly reduced tumor necrosis factor-alpha-induce apoptosis. These results demonstrate for the first time that chymotrypsin B is not only restricted to the pancreas but can function intracellularly as a pro-apoptotic protease.     

Using giant unilamellar lipid vesicle micro-patterns as ultrasmall reaction containers to observe reversible ATP synthesis/hydrolysis of F0F1-ATPase directly

F(0)F(1)-ATPase within chromatophores, which was labeled with pH-sensitive quantum dots, was encapsulated in large unilamellar lipid vesicles (LUVs) through reverse-phase evaporation. Then a microarray of chromatophore-containing LUVs was created using a micro-contact printing (mu-CP) technique. Through controlled dehydration-rehydration of the lipid patterns, a microarray of single chromatophore-containing giant unilamellar lipid vesicles (GUVs) was formed with desired size and uniform shape. The reversible ATP synthesis/hydrolysis of F(0)F(1)-ATPase in GUVs was directly observed by fluorescence microscopy through the fluorescence intensity increase/decrease in the pH-sensitive quantum dots labeled on the outer surface of the chromatophore. To the best of our knowledge, this is the first direct observation of the reversible behavior of F(0)F(1)-ATPase at the bulk scale.     

通过骨盆外测量推算中骨盆径的一元和多元回归方程

本文以126例生育年龄非妊娠女工的髂结节间径、髂前上棘间径、大转子间径及坐骨结节间径为自变量估计因变量中骨盆横径,求出多元回归方程:=—6.89+0.05x_1+0.12x_2+0.23x_3+0.77x_4;以骶耻外径和骨盆倾斜度为自变量估计因变量中骨盆矢径,其回归方程为:=6.09+0.39x_1-0.05x_2。对两方程进行方差分析,其F值分别为4.069和8.26,均具高度显著性,可以应用于临床对中骨盆径的估计以取代X线测量法。     

SD-RLK28 positively regulates pollen hydration on stigmas as a PCP-Bβ receptor in Arabidopsis thaliana

Pollen hydration on dry stigmas is strictly regulated by pollen–stigma interactions in Brassicaceae. Although several related molecular events have been described, the molecular mechanism underlying pollen hydration remains elusive. Multiple B-class pollen coat proteins(PCP-Bs) are involved in pollen hydration. Here, by analyzing the interactions of two PCP-Bs with three Arabidopsis thaliana stigmas strongly expressing S-domain receptor kinase(SD-RLK), we determined that SD-RLK28 directly intera...     

A swine arterivirus deubiquitinase stabilizes two major envelope proteins and promotes production of viral progeny

Arteriviruses are enveloped positive-strand RNA viruses that assemble and egress using the host cell’s exocytic pathway. In previous studies, we demonstrated that most arteriviruses use a unique -2 ribosomal frameshifting mechanism to produce a C-terminally modified variant of their nonstructural protein 2 (nsp2). Like full-length nsp2, the N-terminal domain of this frameshift product, nsp2TF, contains a papain-like protease (PLP2) that has deubiquitinating (DUB) activity, in addition to its role in proteolytic processing of replicase polyproteins. In cells infected with porcine reproductive and respiratory syndrome virus (PRRSV), nsp2TF localizes to compartments of the exocytic pathway, specifically endoplasmic reticulum-Golgi intermediate compartment (ERGIC) and Golgi complex. Here, we show that nsp2TF interacts with the two major viral envelope proteins, the GP5 glycoprotein and membrane (M) protein, which drive the key process of arterivirus assembly and budding. The PRRSV GP5 and M proteins were found to be poly-ubiquitinated, both in an expression system and in cells infected with an nsp2TF-deficient mutant virus. In contrast, ubiquitinated GP5 and M proteins did not accumulate in cells infected with the wild-type, nsp2TF-expressing virus. Further analysis implicated the DUB activity of the nsp2TF PLP2 domain in deconjugation of ubiquitin from GP5/M proteins, thus antagonizing proteasomal degradation of these key viral structural proteins. Our findings suggest that nsp2TF is targeted to the exocytic pathway to reduce proteasome-driven turnover of GP5/M proteins, thus promoting the formation of GP5-M dimers that are critical for arterivirus assembly.