Macro Domain家族成员LRP16是多种核受体的相互作用因子

LRP16基因是macro domain家族成员之一,C末端含有唯一的1个保守的功能结构域. 既往研究表明,该基因具有雌激素反应性,并可通过与雌激素受体α （ERα）相互作用调控其转录活性.近期我研究组发现,LRP16可与雄激素受体（AR）的共激活因子ART-27相互作用.本研究首先通过GST pull-down方法验证LRP16/ART-27/AR三者之间相互作用关系,并用免疫共沉淀实验明确了LRP16与AR存在直接的相互作用,且这种相互作用并不依赖于ART-27的存在;采用GST pull-down进一步明确LRP16与AR相互作用的结构域.结果发现,LRP16通过C端的macro domain结构域与AR的LBD域相互作用;鉴于核受体家族有较高程度的氨基酸序列保守性与功能结构域的相似性,通过GST pull-down验证了LRP16与核受体超家族成员ERβ、GR、PPARα、PPARγ的相互作用,提示LRP16至少还可与ERα以外的5个核受体家族成员相互作用;进一步采用核受体荧光素酶报告基因转染细胞,通过检测荧光素酶活性证实LRP16可增强AR、GR、ERβ、PPARα、PPARγ的转录激活活性.本研究初步证实,macro domain家族成员LRP16可与多个核受体相互作用,并增强其转录激活活性,是核受体家族的共激活因子,为进一步研究LRP16在核受体转录调控中的生理病理学功能奠定基础.     

核受体辅活化子PNRC与孤儿核受体SF1相互作用位点的鉴定

为了阐明核受体辅活化子 (proline richnuclearreceptorcoactivatorprotein ,PNRC)在孤儿核受体类固醇生成因子 1(steroidogenicfactor1,SF1)基因表达调控中的作用 ,采用酵母双杂合分析、缺失突变技术和瞬时转染等研究方法鉴定了PNRC与SF1的相互作用位点 .结果显示 ,PNRC中氨基酸 2 78～ 30 0区域是与SF1相互作用的位点 .该区域富含脯氨酸 ,其中有 1个SH3结合模体 (motif) ,单独的SH3模体不足以与SF1产生有效的相互作用 .瞬时转染分析表明 ,PNRC 2 70 32 7对野生型PNRC的辅激活功能具有负显性抑制效应 .研究结果表明 ,含SH3结合模体的PNRC 2 78 30 0区域是与SF1相互作用的位点     

Identification of CHIP, a Novel Tetratricopeptide Repeat-Containing Protein That Interacts with Heat Shock Proteins and Negatively Regulates Chaperone Functions

The chaperone function of the mammalian 70-kDa heat shock proteins Hsc70 and Hsp70 is modulated by physical interactions with four previously identified chaperone cofactors: Hsp40, BAG-1, the Hsc70-interacting protein Hip, and the Hsc70-Hsp90-organizing protein Hop. Hip and Hop interact with Hsc70 via a tetratricopeptide repeat domain. In a search for additional tetratricopeptide repeat-containing proteins, we have identified a novel 35-kDa cytoplasmic protein, carboxyl terminus of Hsc70-interacting protein (CHIP). CHIP is highly expressed in adult striated muscle in vivo and is expressed broadly in vitro in tissue culture. Hsc70 and Hsp70 were identified as potential interaction partners for this protein in a yeast two-hybrid screen. In vitro binding assays demonstrated direct interactions between CHIP and both Hsc70 and Hsp70, and complexes containing CHIP and Hsc70 were identified in immunoprecipitates of human skeletal muscle cells in vivo. Using glutathione S-transferase fusions, we found that CHIP interacted with the carboxy-terminal residues 540 to 650 of Hsc70, whereas Hsc70 interacted with the amino-terminal residues 1 to 197 (containing the tetratricopeptide domain and an adjacent charged domain) of CHIP. Recombinant CHIP inhibited Hsp40-stimulated ATPase activity of Hsc70 and Hsp70, suggesting that CHIP blocks the forward reaction of the Hsc70-Hsp70 substrate-binding cycle. Consistent with this observation, both luciferase refolding and substrate binding in the presence of Hsp40 and Hsp70 were inhibited by CHIP. Taken together, these results indicate that CHIP decreases net ATPase activity and reduces chaperone efficiency, and they implicate CHIP in the negative regulation of the forward reaction of the Hsc70-Hsp70 substrate-binding cycle.     

Identification and Characterization of the Single-Stranded DNA-Binding Protein of Bacteriophage P1

The genome of bacteriophage P1 harbors a gene coding for a 162-amino-acid protein which shows 66% amino acid sequence identity to the Escherichia coli single-stranded DNA-binding protein (SSB). The expression of the P1 gene is tightly regulated by P1 immunity proteins. It is completely repressed during lysogenic growth and only weakly expressed during lytic growth, as assayed by an ssb-P1/lacZ fusion construct. When cloned on an intermediate-copy-number plasmid, the P1 gene is able to suppress the temperature-sensitive defect of an E. coli ssb mutant, indicating that the two proteins are functionally interchangeable. Many bacteriophages and conjugative plasmids do not rely on the SSB protein provided by their host organism but code for their own SSB proteins. However, the close relationship between SSB-P1 and the SSB protein of the P1 host, E. coli, raises questions about the functional significance of the phage protein.     

Anandamide, a Brain Endogenous Compound, Interacts Specifically with Cannabinoid Receptors and Inhibits Adenylate Cyclase

Abstract: We investigated the role of polyamines and their regulatory enzyme ornithine decarboxylase in N -Methyl-D-aspartate-induced excitotoxicity in embryonic chick retina. N -Methyl-D-aspartate (200 μM) produced an early increase in ornithine decarboxylase activity, putrescine concentration, and Ca²+ entry, leading to selective neuronal death by 30 min. This response was attenuated by the ornithine decarboxylase inhibitor α-difluoromethylornithine and the N -methyl-D-aspartate receptor antagonist 5-aminophosphonovaleric acid. Exogenous putrescine increased intracellular putrescine and spermine levels and reversed neuroprotection by α-difluoromethylornithine, but not by 5-aminophosphonovaleric acid. N -Methyl-D-aspartate-receptor stimulation of putrescine/polyamine synthesis mediates abnormal Ca²+ entry and acute excitotoxic neuronal death. Postreceptor inhibition of the ornithine decar-boxylase/polyamine cascade by α-difluoromethylornithine may provide neuroprotection against N -methyl-D-aspartate-induced excitotoxicity.     

Identification of Protein Domains That Control Proton and Calcium Sensitivity of ASIC1a

The acid-sensing ion channels (ASICs) open in response to extracellular acidic pH, and individual subunits display differential sensitivity to protons and calcium. ASIC1a acts as a high affinity proton sensor, whereas ASIC2a requires substantially greater proton concentrations to activate. Using chimeras composed of ASIC1a and ASIC2a, we determined that two regions of the extracellular domain (residues 87–197 and 323–431) specify the high affinity proton response of ASIC1a. These two regions appear to undergo intersubunit interactions within the multimeric channel to specify proton sensitivity. Single amino acid mutations revealed that amino acids around Asp³⁵⁷ play a prominent role in determining the pH dose response of ASIC1a. Within the same region, mutation F352L abolished PcTx1 modulation of ASIC1a. Surprisingly, we determined that another area of the extracellular domain was required for calcium-dependent regulation of ASIC1a activation, and this region functioned independently of high affinity proton sensing. These results indicate that specific regions play overlapping roles in pH-dependent gating and PcTx1-dependent modulation of ASIC1a activity, whereas a distinct region determines the calcium dependence of ASIC1a activation.The acid-sensing ion channels (ASICs)³ are proton-gated ion channels expressed in neurons throughout the central and peripheral nervous system (1–3). ASICs are activated by extracellular acidosis, and protons act as ligands triggering channel opening (4). Disruption of the accn2 gene (which encodes ASIC1) dramatically reduces proton-gated currents in central neurons and alters a variety of behaviors, including fear, learning, and memory (5, 6). ASIC1 also contributes to neuronal damage and death during the prolonged acidosis accompanying cerebral ischemia (7). Specifically, mice with disruptions in the accn2 gene display 60% smaller lesion size compared with normal mice in models of stroke (8). Application of PcTx1, a venom peptide that prevents ASIC1a activation, is similarly neuroprotective, even when administered hours after injury (8, 9). Thus, ASIC1a represents a novel pharmacological target for the prevention of neuronal death following stroke.Mammals have four genes encoding ASICs (accn1 to -4) that encode at least six different ASIC subunits (1–3, 10). Like all members of the DEG/ENaC family, individual ASIC subunits have two transmembrane regions separated by a large cysteine-rich extracellular region. Three ASIC subunits associate to form homomeric or heteromeric channels with distinct biophysical characteristics (11–14). Specifically, ASIC1a homomeric channels activate at pH values much closer to neutral pH compared with ASIC2a homomeric channels. The high affinity proton sensitivity of ASIC1a plays a prominent role in acidosis-induced neuronal death, and modulators that alter the pH dose response of ASIC1a affect neuronal sensitivity to prolonged acidosis (8, 9, 15). For example, the neuroprotective venom peptide PcTx1 increases the proton sensitivity of the ASIC1a channel, allowing the channel to desensitize at neutral pH and become unresponsive to subsequent acidic shifts in pH (16, 17). The large extracellular region of ASIC1a is thought to be the site of proton/modulator interaction and governs the characteristics of channel gating (10, 11, 18). However, the exact molecular mechanisms defining ASIC1a activation and the protein domains that are responsible for the apparent proton sensitivity of ASIC1a remain unclear. Here, we used chimeras containing specific regions from both ASIC1a and ASIC2a to identify the specific protein regions that confer high affinity proton sensing, PcTx1 sensitivity, and calcium modulation to ASIC1a.     

Identification of a Maize Locus That Modulates the Hypersensitive Defense Response,Using Mutant-Assisted Gene Identification and Characterization

Potentially useful naturally occurring genetic variation is often difficult to identify as the effects of individual genes are subtle and difficult to observe. In this study, a novel genetic technique called Mutant-Assisted Gene Identification and Characterization is used to identify naturally occurring loci modulating the hypersensitive defense response (HR) in maize. Mutant-Assisted Gene Identification and Characterization facilitates the identification of naturally occurring alleles underlying phenotypic variation from diverse germplasm, using a mutant phenotype as a “reporter.” In this study the reporter phenotype was caused by a partially dominant autoactive disease resistance gene, Rp1-D21, which caused HR lesions to form spontaneously all over the plant. Here it is demonstrated that the Rp1-D21 phenotype is profoundly affected by genetic background. By crossing the Rp1-D21 gene into the IBM mapping population, it was possible to map and identify Hrml1 on chromosome 10, a locus responsible for modulating the HR phenotype conferred by Rp1-D21. Other loci with smaller effects were identified on chromosomes 1 and 9. These results demonstrate that Mutant-Assisted Gene Identification and Characterization is a viable approach for identifying naturally occurring useful genetic variation.POTENTIALLY useful naturally occurring genetic variation is often difficult to identify as the effects of individual genes are subtle and difficult to observe. Furthermore, so many different alleles are available that it is a major challenge just to sift through the enormous diversity available. To this end, we recently conceptualized a simple yet effective method to discover and characterize variation present naturally in plant germplasm (Johal et al. 2008). This method, Mutant-Assisted Gene Identification and Characterization, makes use of a mutant phenotype for a gene affecting the trait of interest as a reporter to discover and analyze relevant, interacting genes present naturally in diverse germplasm. Mutant-Assisted Gene Identification and Characterization involves crossing a mutant to diverse germplasm and then evaluating the mutant progeny for transgressive changes (both suppressed and severe) in the mutant phenotype(s). If the mutation is recessive, the population needs to be advanced to the F₂ generation to be able to detect and analyze such variation. However, for a dominant or partially dominant mutant, evaluations can be made immediately in the F₁ to discover lines that contain suppressors or enhancers of the trait (mutation) under study. Mutant F₁ progenies from such crosses can then be propagated further to identify, map, and clone genes/QTL that affect the trait positively or negatively. In the case of maize and other species for which genetically characterized mapping populations are available, modifying loci can be rapidly mapped by crossing a mutant line to each member of a mapping population and evaluating the resulting F₁ families. In this study we provide a proof-of-concept for the Mutant-Assisted Gene Identification and Characterization technique, using it to identify loci involved in the defense response of maize.Plants are constantly exposed to numerous potential pathogens with diverse modes of attack. Nevertheless, it is rather rare to see plants succumbing to disease. One key reason for this is the presence of a highly effective and inducible defense system, a major component of which is the hypersensitive response (HR). HR is usually associated with a specific recognition event and is activated after other nonspecific resistance mechanisms have been overcome or evaded (see Bent and Mackey 2007). Although it was initially coined to refer to the rapid collapse of cells at the site of infection, over the years the term HR has been used to refer to both cell death and the associated induction of a number of other defense responses, including the accumulation of phytoalexins and pathogenesis-related (PR) proteins at the site of infection, to name a few (Mur et al. 2007). Reactive oxygen species such as superoxide and H₂O₂ appear to be causally involved in cell death underlying the HR response (Jones and Dangl 2006).HR is under the control of a subset of disease-resistance genes, commonly referred to as R genes. These R genes specifically recognize matching avirulence (Avr) effectors from the pathogen. Many R genes encode products containing a nucleotide-binding site (NBS) domain in the middle of the protein and a leucine-rich repeat (LRR) domain at the C-terminal end (Bent and Mackey 2007). R proteins are involved both in the recognition of the pathogen and the subsequent induction of the HR response. How R proteins remain in a quiescent but “vigilant” state remains to be established. Certain mutations in R genes have been found that abolish their dependence on AVR proteins for activation. Such aberrant R genes mostly behave as dominant or partially dominant alleles and trigger the HR constitutively in the absence of the pathogen (Hu et al. 1996; Zhang et al. 2003; Dodds et al. 2006). Two consequences of such “autoactive” or “ectopically active” R genes are a massive induction of cell death and the consequential stunting of the organism (Dodds et al. 2006). Although autoactive R genes have been found to exist in many plant species, the first few examples came from the maize Rp1 locus, which confers race-specific resistance to common rust, caused by Puccinia sorghi (Hu et al. 1996). Such autoactive R genes can be used to investigate HR genetics and etiology in the absence of confounding effects from the pathogen and constitute an excellent candidate for analysis using Mutant-Assisted Gene Identification and Characterization.The details of the HR cell death reaction as well as the pathway(s) that link R gene activation with the HR remain unclear (Mur et al. 2007). Despite considerable research over the past decade, only a few components have been found thus far. Some of these, Ndr1, Eds1, Pad4, Rar1, and Sgt1, were identified in mutagenesis screens conducted to identify mutants that failed to undergo an HR reaction in response to infection by an avirulent pathogen (reviewed in Bent and Mackey 2007). A few others, RIN4, for example, were identified in yeast two-hybrid assays using an NBS–LRR protein as bait (Mackey et al. 2003). Recently, an Arabidopsis gain-of-function mutant that carries a point mutation in an R gene analog (a gene with the structure of an R gene but not known to be involved in resistance to any pathogen) was used to isolate a few more potential genes in the HR pathway in a second site suppressor approach following mutagenesis with ethane methyl sulfonate (EMS) (Palma et al. 2005; Zhang and Li 2005; Goritschnig et al. 2007). A problem with approaches based on intentional mutagenesis is that they fail to uncover genes that have either redundant or essential functions. One way to avoid this problem would be to seek naturally occurring allelic variants affecting HR. Such natural variation is pervasive in all species, being generated and selected for over millions of years of evolution.Although natural variation has served as a constant provider of the R genes in all plant species, natural variability has not been tapped as a tool for understanding other aspects of the disease-resistance response (Holub 2007). The Rp1-D21 gene is an autoactive allele from the maize Rp1 disease-resistance locus that initiates HR randomly all over the plant (Pryor 1993; Collins et al. 1999; Sun et al. 2001). Our objective for this study was to use the Rp1-D21 gene phenotype as a test case for the Mutant-Assisted Gene Identification and Characterization approach. We show here that enormous variation exists in the maize germplasm that is capable of affecting the HR response positively or negatively and we identify loci that modulate expression of the HR phenotype segregating in the well-known Intermated B73 × Mo17 (IBM) advanced intercross line (AIL) population (Coe et al. 2002; Lee et al. 2002). This constitutes the first demonstration of the utility of the Mutant-Assisted Gene Identification and Characterization approach—an approach that is likely to prove widely applicable.     

Identification of a Translation Initiation Factor 3 (eIF3) Core Complex, Conserved in Yeast and Mammals, That Interacts with eIF5

Only five of the nine subunits of human eukaryotic translation initiation factor 3 (eIF3) have recognizable homologs encoded in the Saccharomyces cerevisiae genome, and only two of these (Prt1p and Tif34p) were identified previously as subunits of yeast eIF3. We purified a polyhistidine-tagged form of Prt1p (His-Prt1p) by Ni²⁺ affinity and gel filtration chromatography and obtained a complex of ≈600 kDa composed of six polypeptides whose copurification was completely dependent on the polyhistidine tag on His-Prt1p. All five polypeptides associated with His-Prt1p were identified by mass spectrometry, and four were found to be the other putative homologs of human eIF3 subunits encoded in S. cerevisiae: YBR079c/Tif32p, Nip1p, Tif34p, and YDR429c/Tif35p. The fifth Prt1p-associated protein was eIF5, an initiation factor not previously known to interact with eIF3. The purified complex could rescue Met-tRNA_i^Met binding to 40S ribosomes in defective extracts from a prt1 mutant or extracts from which Nip1p had been depleted, indicating that it possesses a known biochemical activity of eIF3. These findings suggest that Tif32p, Nip1p, Prt1p, Tif34p, and Tif35p comprise an eIF3 core complex, conserved between yeast and mammals, that stably interacts with eIF5. Nip1p bound to eIF5 in yeast two-hybrid and in vitro protein binding assays. Interestingly, Sui1p also interacts with Nip1p, and both eIF5 and Sui1p have been implicated in accurate recognition of the AUG start codon. Thus, eIF5 and Sui1p may be recruited to the 40S ribosomes through physical interactions with the Nip1p subunit of eIF3.     

Identification,Purification, and Characterization of Transpeptidase and Glycosyltransferase Domains of Streptococcus pneumoniae Penicillin-Binding Protein 1a

Resistance to β-lactam antibiotics in Streptococcus pneumoniae is due to alteration of penicillin-binding proteins (PBPs). S. pneumoniae PBP 1a belongs to the class A high-molecular-mass PBPs, which harbor transpeptidase (TP) and glycosyltransferase (GT) activities. The GT active site represents a new potential target for the generation of novel nonpenicillin antibiotics. The 683-amino-acid extracellular region of PBP 1a (PBP 1a*) was expressed in Escherichia coli as a GST fusion protein. The GST-PBP 1a* soluble protein was purified, and its domain organization was revealed by limited proteolysis. A protease-resistant fragment spanning Ser 264 to Arg 653 exhibited a reactivity profile against both β-lactams and substrate analogues similar to that of the parent protein. This protein fragment represents the TP domain. The GT domain (Ser 37 to Lys 263) was expressed as a recombinant GST fusion protein. Protection by moenomycin of the GT domain against trypsin degradation was interpreted as an interaction between the GT domain and the moenomycin.The synthesis of the bacterial cell wall requires cytoplasmic and periplasmic enzymes. The final steps of peptidoglycan biosynthesis occur outside the cytoplasmic membrane, and they are catalyzed by membrane-bound penicillin-binding proteins (PBPs). PBPs play essential roles in cell division and morphology (6, 20, 31). Based upon their molecular sizes and amino acid sequence similarities, PBPs can be classified into two groups (6): low-molecular-weight (low-M_r) PBPs, which act as d,d-carboxypeptidases, and high-molecular-weight (high-M_r) PBPs, which carry transpeptidase (TP) and glycosyltransferase (GT) activities. The high-M_r group can be further divided into bifunctional enzymes with TP and GT activities (class A) and monofunctional TP enzymes (class B).β-Lactam antibiotics bind with high affinity specifically to d,d-carboxypeptidase and TP domains because of their structural similarity to the natural substrates, the stem peptides. This binding results in the formation of a covalent acyl-PBP enzyme complex, leading to the inactivation of PBPs.High-M_r PBPs are multidomain proteins (6). The three-dimensional structure of Streptococcus pneumoniae PBP 2x (class B high-M_r PBP) illustrates this domain organization (25). The only non-penicillin-binding domain of known function is the GT domain, corresponding to the N-terminal region of class A PBPs. This GT activity, clearly identified in Escherichia coli PBP 1b, is difficult to measure (23, 29, 31–35). It is insensitive to penicillin but sensitive to moenomycin, an antibiotic which is not used for human therapy (23, 29, 32, 33).S. pneumoniae is one of the major human pathogens of the upper respiratory tract, causing pneumonia, meningitis, and ear infections. Six PBPs have been identified in S. pneumoniae: high-M_r PBPs 1a, 1b, 2a, 2x, and 2b and low-M_r PBP 3 (8). PBPs 1a, 1b, and 2a belong to class A, while PBPs 2x and 2b are monofunctional class B proteins. Deletion of pbp2x and pbp2b in S. pneumoniae is lethal for the bacteria, while the deletion of pbp1a is tolerated (11), probably due to compensation by PBP 1b. This has been observed for E. coli class A PBP 1a, whose deletion can be compensated for by PBP 1b (36). In clinical isolates of resistant pneumococci, pbp1a, pbp2x, and pbp2b genes were shown to present a mosaic organization, encoding PBPs with reduced affinity for β-lactam antibiotics (2, 5, 15, 18). The specific resistance to ceftriaxone and cefotaxime of S. pneumoniae from the hospital environment is mediated by modification of PBP 2x and PBP 1a (22). Furthermore, gene transfer of pbp1a, pbp2x, and pbp2b from resistant strains conferred penicillin resistance on sensitive S. pneumoniae strains under laboratory conditions (2–4, 14, 15, 27, 30).The effort to overcome resistance to antibiotics in S. pneumoniae might therefore benefit from a detailed understanding of the molecular basis of TP and GT activities. The GT domain represents a new potential target for novel nonpenicillin antibiotics. Here, we delineate the GT and TP domains of S. pneumoniae PBP 1a* (a water-soluble form of PBP 1a) by limited proteolytic digestion and expression of recombinant domains. The TP activity of PBP 1a* and that of the isolated TP domain were compared. We also present evidence for an interaction between the isolated GT domain and moenomycin.