Enhanced moisture stability of metal halide perovskite solar cells based on sulfur-oleylamine surface modification.

As one of the most promising light-harvesting materials, perovskites have drawn tremendous attention for their unique advantages, such as high efficiency, low cost and facile fabrication compared with other photovoltaic materials. Nevertheless, poor moisture tolerance of the perovskites greatly hampers the operation of such devices and hinders their commercialization. Herein, we demonstrate a facile dipping treatment using sulfur-oleylamine solution for surface atomic modulation of perovskite films. Oleylammonium polysulfides (OPs) would be self-assembled on the etched perovskite film as an ultrathin outer layer. This layer could passivate the surface chemical activity of the outer perovskite layers. Moreover, the hydrophobic OPs significantly enhance moisture stability of such devices. As a result, the obtained device without encapsulation retains more than 70% of its initial power conversion efficiency (PCE) after 14 days of exposure to a relative humidity of 40 ± 10%.

Structural basis for recognition of the third SH3 domain of full-length R85 (R85FL)/ponsin by ataxin-7.

Ataxin-7 (Atx7) is a component of the nuclear transcription co-activator complex; its polyglutamine (polyQ) expansion may cause nuclear accumulation and recruit numerous proteins to the intranuclear inclusion bodies. Full-length R85 (R85FL) is such a protein sequestered by polyQ-expanded Atx7. Here, we report that Atx7 specifically interacts with the third SH3 domain (SH3C) of R85FL through its second portion of proline-rich region (PRR). NMR structural analysis of the SH3C domain and its complex with PRR revealed that SH3C contains a large negatively charged surface for binding with the RRTR motif of Atx7. Microscopy imaging demonstrated that sequestration of R85FL by the polyQ-expanded Atx7 in cell is mediated by this specific SH3C-PRR interaction, which is implicated in the pathogenesis of spinocerebellar ataxia 7.

The C-terminal helices of heat shock protein 70 are essential for J-domain binding and ATPase activation.

The J-domain co-chaperones work together with the heat shock protein 70 (HSP70) chaperone to regulate many cellular events, but the mechanism underlying the J-domain-mediated HSP70 function remains elusive. We studied the interaction between human-inducible HSP70 and Homo sapiens J-domain protein (HSJ1a), a J domain and UIM motif-containing co-chaperone. The J domain of HSJ1a shares a conserved structure with other J domains from both eukaryotic and prokaryotic species, and it mediates the interaction with and the ATPase cycle of HSP70. Our in vitro study corroborates that the N terminus of HSP70 including the ATPase domain and the substrate-binding ß-subdomain is not sufficient to bind with the J domain of HSJ1a. The C-terminal helical α-subdomain of HSP70, which was considered to function as a lid of the substrate-binding domain, is crucial for binding with the J domain of HSJ1a and stimulating the ATPase activity of HSP70. These fluctuating helices are likely to contribute to a proper conformation of HSP70 for J-domain binding other than directly bind with the J domain. Our findings provide an alternative mechanism of allosteric activation for functional regulation of HSP70 by its J-domain co-chaperones.

Length of the active-site crossover loop defines the substrate specificity of ubiquitin C-terminal hydrolases for ubiquitin chains.

UCHs [Ub (ubiquitin) C-terminal hydrolases] are a family of deubiquitinating enzymes that are often thought to only remove small C-terminal peptide tails from Ub adducts. Among the four UCHs identified to date, neither UCH-L3 nor UCH-L1 can catalyse the hydrolysis of isopeptide Ub chains, but UCH-L5 can when it is present in the PA700 complex of the proteasome. In the present paper, we report that the UCH domain of UCH-L5, different from UCH-L1 and UCH-L3, by itself can process the K48-diUb (Lys48-linked di-ubiquitin) substrate by cleaving the isopeptide bond between two Ub units. The catalytic specificity of the four UCHs is dependent on the length of the active-site crossover loop. The UCH domain with a long crossover loop (usually >14 residues), such as that of UCH-L5 or BAP1 [BRCA1 (breast cancer early-onset 1)-associated protein 1], is able to cleave both small and large Ub derivatives, whereas the one with a short loop can only process small Ub derivatives. We also found that elongation of the crossover loop enables UCH-L1 to have isopeptidase activity for K48-diUb in a length-dependent manner. Thus the loop length of UCHs defines their substrate specificity for diUb chains, suggesting that the chain flexibility of the crossover loop plays an important role in determining its catalytic activity and substrate specificity for cleaving isopeptide Ub chains.

A fluorescence assay for elucidating the substrate specificities of deubiquitinating enzymes.

Ubiquitin C-terminal hydrolases (UCHs) are a representative family of deubiquitinating enzymes (DUBs), which specifically cleave ubiquitin (Ub) chains or extensions. Here we present a convenient method for characterizing the substrate specificities of various UCHs by fluorescently mutated Ub-fusion proteins (Ub(F45W)-Xaa) and di-ubiquitin chains (Ub(F45W)-diUb). After removal of the intact substrate by Ni(2+)-NTA affinity, the enzymatic activities of UCHs were quantitatively determined by recording fluorescence of the Ub(F45W) product. The results show that three UCHs, i.e. UCH-L1, UCH-L3 and UCH37/UCH-L5, are distinct in their substrate specificities for the Ub-fusions and diUb chains. This assay method may also be applied to study the enzymatic activities and substrate specificities of other DUBs.

Co-chaperone HSJ1a dually regulates the proteasomal degradation of ataxin-3.

Homo sapiens J domain protein (HSJ1) is a J-domain containing co-chaperone that is known to stimulate ATPase activity of HSP70 chaperone, while it also harbors two ubiquitin (Ub)-interacting motifs (UIMs) that may bind with ubiquitinated substrates and potentially function in protein degradation. We studied the effects of HSJ1a on the protein levels of both normal and the disease--related polyQ-expanded forms of ataxin-3 (Atx3) in cells. The results demonstrate that the N-terminal J-domain and the C-terminal UIM domain of HSJ1a exert opposite functions in regulating the protein level of cellular overexpressed Atx3. This dual regulation is dependent on the binding of the J-domain with HSP70, and the UIM domain with polyUb chains. The J-domain down-regulates the protein level of Atx3 through HSP70 mediated proteasomal degradation, while the UIM domain may alleviate this process via maintaining the ubiquitinated Atx3. We propose that co-chaperone HSJ1a orchestrates the balance of substrates in stressed cells in a Yin-Yang manner.

A conserved motif within RAP1 has diversified roles in telomere protection and regulation in different organisms.

Repressor activator protein 1 (RAP1) is the most highly conserved telomere protein. It is involved in protecting chromosome ends in fission yeast and promoting gene silencing in Saccharomyces cerevisiae, whereas it represses homology-directed recombination at telomeres in mammals. To understand how RAP1 has such diverse functions at telomeres, we solved the crystal or solution structures of the RAP1 C-terminal (RCT) domains of RAP1 from multiple organisms in complex with their respective protein-binding partners. Our analysis establishes RAP1(RCT) as an evolutionarily conserved protein-protein interaction module. In mammalian and fission yeast cells, this module interacts with TRF2 and Taz1, respectively, targeting RAP1 to chromosome ends for telomere protection. In contrast, S. cerevisiae RAP1 uses its RCT domain to recruit Sir3 to telomeres to mediate gene silencing. Together, our results show that, depending on the organism, the evolutionarily conserved RAP1 RCT motif has diverse functional roles at telomeres.

Domain analysis reveals that a deubiquitinating enzyme USP13 performs non-activating catalysis for Lys63-linked polyubiquitin.

Deubiquitination is a reverse process of cellular ubiquitination important for many biological events. Ubiquitin (Ub)-specific protease 13 (USP13) is an ortholog of USP5 implicated in catalyzing hydrolysis of various Ub chains, but its enzymatic properties and catalytic regulation remain to be explored. Here we report studies of the roles of the Ub-binding domains of USP13 in regulatory catalysis by biochemical and NMR structural approaches. Our data demonstrate that USP13, distinct from USP5, exhibits a weak deubiquitinating activity preferring to Lys63-linked polyubiquitin (K63-polyUb) in a non-activation manner. The zinc finger (ZnF) domain of USP13 shares a similar fold with that of USP5, but it cannot bind with Ub, so that USP13 has lost its ability to be activated by free Ub. Substitution of the ZnF domain with that of USP5 confers USP13 the property of catalytic activation. The tandem Ub-associated (UBA) domains of USP13 can bind with different types of diUb but preferentially with K63-linked, providing a possible explanation for the weak activity preferring to K63-polyUb. USP13 can also regulate the protein level of CD3δ in cells, probably depending on its weak deubiquitinating activity and the Ub-binding properties of the UBA domains. Thus, the non-activating catalysis of USP13 for K63-polyUb chains implies that it may function differently from USP5 in cellular deubiquitination processes.

Structural transformation of the tandem ubiquitin-interacting motifs in ataxin-3 and their cooperative interactions with ubiquitin chains.

The ubiquitin-interacting motif (UIM) is a short peptide with dual function of binding ubiquitin (Ub) and promoting ubiquitination. We elucidated the structures and dynamics of the tandem UIMs of ataxin-3 (AT3-UIM12) both in free and Ub-bound forms. The solution structure of free AT3-UIM12 consists of two α-helices and a flexible linker, whereas that of the Ub-bound form is much more compact with hydrophobic contacts between the two helices. NMR dynamics indicates that the flexible linker becomes rigid when AT3-UIM12 binds with Ub. Isothermal titration calorimetry and NMR titration demonstrate that AT3-UIM12 binds diUb with two distinct affinities, and the linker plays a critical role in association of the two helices in diUb binding. These results provide an implication that the tandem UIM12 interacts with Ub or diUb in a cooperative manner through an allosteric effect and dynamics change of the linker region, which might be related to its recognitions with various Ub chains and ubiquitinated substrates.

Arsenic trioxide controls the fate of the PML-RARalpha oncoprotein by directly binding PML.

Arsenic, an ancient drug used in traditional Chinese medicine, has attracted worldwide interest because it shows substantial anticancer activity in patients with acute promyelocytic leukemia (APL). Arsenic trioxide (As2O3) exerts its therapeutic effect by promoting degradation of an oncogenic protein that drives the growth of APL cells, PML-RARalpha (a fusion protein containing sequences from the PML zinc finger protein and retinoic acid receptor alpha). PML and PML-RARalpha degradation is triggered by their SUMOylation, but the mechanism by which As2O3 induces this posttranslational modification is unclear. Here we show that arsenic binds directly to cysteine residues in zinc fingers located within the RBCC domain of PML-RARalpha and PML. Arsenic binding induces PML oligomerization, which increases its interaction with the small ubiquitin-like protein modifier (SUMO)-conjugating enzyme UBC9, resulting in enhanced SUMOylation and degradation. The identification of PML as a direct target of As2O3 provides new insights into the drug's mechanism of action and its specificity for APL.

Interaction with synphilin-1 promotes inclusion formation of alpha-synuclein: mechanistic insights and pathological implication.

alpha-Synuclein (alpha-Syn) is the major component of Lewy bodies (LBs) deposited in the brains of patients with Parkinson's disease. Synphilin-1 (Sph1) is a novel alpha-Syn-interacting protein also present in the LBs. However, the roles of alpha-Syn-Sph1 interaction in LB formation and in the related pathogenesis are still unclear. We have studied the interaction between alpha-Syn and Sph1 by biochemical and structural approaches and found that the central coiled-coil domain of Sph1 specifically interacts with the N-terminal stretch of alpha-Syn. When overexpressed in HEK 293T cells, Sph1 forms inclusions together with alpha-Syn, but the Sph1-positive inclusions cannot recruit the N-terminally truncated alpha-Syn. The central portion of Sph1 can also recruit alpha-Syn and induce inclusion formation through its coiled-coil domain. These observations demonstrate that the alpha-Syn-Sph1 interaction significantly promotes the formation of cytoplasmic alpha-Syn inclusions, which may have implications for LB formation in neural cells. We have also elucidated solution structure of the coiled-coil domain of Sph1 and its interaction with the N-terminal peptide of alpha-Syn. The specific interaction between alpha-Syn and Sph1 provides mechanistic insights into the inclusion-body formation in cells and pathological implication in Parkinson's disease.

[Carrying rate of Neissria meningitides in a healthy population in the Mianzhu post-earthquake residential area].

OBJECTIVE: To predict the possibility of epidemic outbreak of meningitis by testing Neissria Meningitides in a healthy population in the Mianzhu post-earthquake residential area. METHODS: A simple random sampling strategy was adopted to collect 887 throat swabs from a healthy population in the Mainzhu post-earthquake residential area. The TaqMan assay were performed to detect Neissria Meningitides. RESULTS: Three positive samples were identified. CONCLUSION: The carrying rate of Neissria Meningitides is not high enough to bring about an epidemic outbreak of Meningitis. However, efforts to maintain a hygienic environment in the post-earthquake residential area should be continued.

Structural basis for ubiquitin recognition by a novel domain from human phospholipase A2-activating protein.

Ubiquitin (Ub) is an essential modifier conserved in all eukaryotes from yeast to human. Phospholipase A(2)-activating protein (PLAA), a mammalian homolog of yeast DOA1/UFD3, has been proposed to be able to bind with Ub, which plays important roles in endoplasmic reticulum-associated degradation, vesicle formation, and DNA damage response. We have identified a core domain from the PLAA family ubiquitin-binding region of human PLAA (residues 386-465, namely PFUC) that can bind Ub and elucidated its solution structure and Ub-binding mode by NMR approaches. The PFUC domain possesses equal population of two conformers in solution by cis/trans-isomerization, whereas the two isomers exhibit almost equivalent Ub binding abilities. This domain structure takes a novel fold consisting of four beta-strands and two alpha-helices, and the Ub-binding site on PFUC locates in the surface of alpha2-helix, which is to some extent analogous to those of UBA, CUE, and UIM domains. This study provides structural basis and biochemical information for Ub recognition of the novel PFU domain from a PLAA family protein that may connect ubiquitination and degradation in endoplasmic reticulum-associated degradation.

[Development of a molecular beacon real-time PCR for the rapid detection of Mycobacterium tuberculosis].

OBJECTIVE: To develop a molecular beacon real-time PCR for rapid detection of Mycobacterium tuberculosis. METHOD: One set of primers was selected from the IS6110 gene in GenBank and the corresponding molecular beacon probe was designed. The specificity and sensitivity of the developed method were evaluated by tested with 10 different bacteria species. The developed assay were also applied to the diagnosis of tuberculosis. RESULTS: Only Mycobacterium tuberculosis strains possessing IS6110 gene generated fluorescent signals, and no cross reaction was observed with other 9 bacteria. The detection limit was 4 copies/PCR reaction. 100 Mycobacterium tuberculosis strains were positive tested by Real-time PCR. CONCLUSION: The established molecular beacon real-time PCR is a rapid, specific and sensitive method, and is a beneficial supplement of traditional methods for the tuberculosis diagnosis.

Differential ubiquitin binding of the UBA domains from human c-Cbl and Cbl-b: NMR structural and biochemical insights.

The Cbl proteins, RING-type E3 ubiquitin ligases, are responsible for ubiquitinating the activated tyrosine kinases and targeting them for degradation. Both c-Cbl and Cbl-b have a UBA (ubiquitin-associated) domain at their C-terminal ends, and these two UBA domains share a high sequence similarity (75%). However, only the UBA from Cbl-b, but not from c-Cbl, can bind ubiquitin (Ub). To understand the mechanism by which the UBA domains specifically interact with Ub with different affinities, we determined the solution NMR structures of these two UBA domains, cUBA from human c-Cbl and UBAb from Cbl-b. Their structures show that these two UBA domains share the same fold, a compact three-helix bundle, highly resembling the typical UBA fold. Chemical shift perturbation experiments reveal that the helix-1 and loop-1 of UBAb form a predominately hydrophobic surface for Ub binding. By comparing the Ub-interacting surface on UBAb and its counterpart on cUBA, we find that the hydrophobic patch on cUBA is interrupted by a negatively charged residue Glu12. Fluorescence titration data show that the Ala12Glu mutant of UBAb completely loses the ability to bind Ub, whereas the mutation disrupting the dimerization has no significant effect on Ub binding. This study provides structural and biochemical insights into the Ub binding specificities of the Cbl UBA domains, in which the hydrophobic surface distribution on the first helix plays crucial roles in their differential affinities for Ub binding. That is, the amino acid residue diversity in the helix-1 region, but not the dimerization, determines the abilities of various UBA domains binding with Ub.