Structural insights into a novel histone demethylase PHF8

Dynamic regulation of histone methylation/demethylation plays an important role during development. Mutations and truncations in human plant homeodomain （PHD） finger protein 8 （PHF8） are associated with X-linked mental retardation and facial anomalies, such as a long face, broad nasal tip, cleft lip/cleft palate and large hands, yet its molecular function and structural basis remain unclear. Here, we report the crystal structures of the catalytic core of PHF8 with or without α-ketoglutarate （α-KG） at high resolution. Biochemical and structural studies reveal that PHF8 is a novel histone demethylase specific for di- and mono-methylated histone H3 lysine 9 （H3K9me2/1）, but not for H3K9me3. Our analyses also reveal how human PHF8 discriminates between methylation states and achieves sequence specificity for methylated H3K9. The in vitro demethylation assay also showed that the F279S mutant observed in clinical patients possesses no demethylation activity, suggesting that loss of enzymatic activity is crucial for pathogenesis of PHF8 patients. Taken together, these results will shed light on the molecular mechanism underlying PHF8-associated developmental and neurological diseases.

PRMT5 regulates Golgi apparatus structure through methylation of the golgin GM130

Maintenance of the Golgi apparatus （GA） structure and function depends on Golgi matrix proteins. The posttranslational modification of Golgi proteins such as phosphorylation of members of the golgin and GRASP families is important for determining Golgi architecture. Some Golgi proteins including golgin-84 are also known to be methylated, but the function of golgin methylation remains unclear. Here, we show that the protein arginine methyltransferase 5 （PRMT5） localizes to the GA and forms complexes with several components involved in GA ribbon formation and vesicle tethering. PRMT5 interacts with the golgin GM130, and depletion of PRMT5 causes defects in Golgi ribbon formation. Furthermore, PRMT5 methylates N-terminal arginines in GM130, and such arginine methylation appears critical for GA ribbon formation. Our findings reveal a molecular mechanism by which PRMT5-dependent arginine methylation of GM130 controls the maintenance of GA architecture.

Synthesis and flocculation characteristics of cationic modified corncob: A novel polymeric flocculant

A novel organic polymeric flocculant was synthesized by grafting cationic etherifying monomer (3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC) onto the backbone of corncob powder (CP,F≤ 30mm). The synthetic reaction between CP and CHPTAC was initiated by hydroxyl radical made from Fenton reagent(H2O2-FeSO4). The alkalization process andsynthetic reaction conditions were optimized byva- rying several parameters affecting grafting efficiency, such as NaOH dose, monomer concentration, reaction temperature and time and distilled water dose. The synthesized cationicflocculant was characterized by elemental analysis,Fourier-transform infrared spectrometer andscanning electron microscope techniques. Itwas concluded that the backbone of CP have been grafted cationic etherifying monomer. The flocculation characteristics in 0.25% (w/v) kaolin suspensions was compared with some of thecommercial flocculants available in markets,and the results demonstrated the synthesized cationic flocculation has superiority as a novel flocculant.

Crystal structure of the C-terminal domain of the ε subunit of human translation initiation factor eIF2B

Eukaryotic translation initiation factor eIF2B,the guanine nucleotide exchange factor(GEF)for eIF2,catalyzes conversion of eIF2·GDP to eIF2·GTP.The eIF2B is composed of five subunits,α,β,γ,δandε,within which theεsubunit is responsible for catalyzing the guanine exchange reaction.Here we present the crystal structure of the C-terminal domain of human eIF2Bε(eIF2Bε-CTD)at 2.0-Åresolution.The structure resembles a HEAT motif and three charge-rich areas on its surface can be identified.When compared to yeast eIF2Bε-CTD,one area involves highly conserved AA boxes while the other two are only partially conserved.In addition,the previously reported mutations in human eIF2Bε-CTD,which are related to the loss of the GEF activity and human VWM disease,have been discussed.Based on the structure,most of such mutations tend to destabilize the HEAT motif.

Allosteric conformational changes of G proteins upon its interaction with membrane and GPCR

Current resolved structures of GPCRs and G protein complexes provided important insights into G protein activation. However, the binding or dissociation of GPCRs with G protein is instantaneous and highly dynamic in the intracellular environment. The conformational dynamic of G protein still needs to be addressed. In this study, we applied ^(19)F solution NMR spectroscopy to monitor the conformational changes of G protein upon interact with detergent mimicking membrane and receptor. Our results show that there are two states equilibria in the G_(α)in apo states. The interaction of G_(α)with detergents will accelerate this conformational transformation and induce a state that tends to bind to GPCRs. Finally, the G_(α)proteins presented a fully activation state when they coupled to GPCRs.

Study on the chaperone properties of conserved GTPases

As a large family of hydrolases,GTPases are widespread in cells and play the very important biological function of hydrolyzing GTP into GDP and inorganic phosphate through binding with it.GTPases are involved in cell cycle regulation,protein synthesis,and protein transportation.Chaperones can facilitate the folding or refolding of nascent peptides and denatured proteins to their native states.However,chaperones do not occur in the native structures in which they can perform their normal biological functions.In the current study,the chaperone activity of the conserved GTPases of Escherichia coli is tested by the chemical denaturation and chaperone-assisted renaturation of citrate synthase andα-glucosidase.The effects of ribosomes and nucleotides on the chaperone activity are also examined.Our data indicate that these conserved GTPases have chaperone properties,and may be ancestral protein folding factors that have appeared before dedicated chaperones.