[A Qualitative Proteome-Wide Lysine Succinylation Profiling of Tea Revealed its Involvement in Primary Metabolism]

Lysine succinylation of proteins has potential impacts on protein structure and function, which occurs on post-translation level. However, the information about the succinylation of proteins in tea plants is limited. In the present study, the significant signal of succinylation in tea plants was found by western blot. Subsequently, we performed a qualitative analysis to globally identify the lysine succinylation of proteins using high accuracy nano LC-MS/MS combined with affinity purification. As a result, a total of 142 lysine succinylation sites were identified on 86 proteins in tea leaves. The identified succinylated proteins were involved in various biological processes and a large proportion of the succinylation sites were presented on proteins in the primary metabolism, including glyoxylate and dicarboxylate metabolism, TCA cycle and glycine, serine and threonine metabolism. Moreover, 10 new succinylation sites were detected on histones in tea leaves. The results suggest that succinylated proteins in tea plants might play critical regulatory roles in biological processes, especially in the primary metabolism. This study not only comprehensively analyzed the lysine succinylome in tea plants, but also provided valuable information for further investigating the functions of lysine succinylation in tea plants.

[Study of epidemic area on Tsutsugamushi disease in Taizhou from 2013 to 2014]

Objective: To study the epidemiological characteristics of tsutsugamushi disease, and to confirm the existence of the disease's epidemic foci in Taizhou. Methods: From 2013 to 2014, Dongxing town hospital and Xingqiao town hospital were selected as specimen collection sites in Jingjiang city. Blood samples (5 ml) were collected from 40 patients with acute tsutsugamushi disease. A total of 59 rodents were captured with cage night method in the survey sites at 5, 7, 9, 10, and 11 months in 2013, from which, the spleen, liver, and kidney specimens were selected. Chigger mites were captured by small blackboard method and from the ears of the captured rodents. A total of 226 small blackboards were laid, 27 mites were captured, and the samples were grounded into suspension. Nested-polymerase chain reaction and cell and tissue culture techniques were used to test the specimen from the probable patients, host animals and chigger mites. Results: Among the 40 acute tsutsugamushi disease blood samples, 29 were found to meet the test requirements, 17 were positive for orientia tsutsugamushi nucleic acid with 59% of the positive rate, and 1 stran orientia tsutsugamushi was isolated. 59 rats were captured and the density of mice was 5.5%. Among them, there were 26 Mus musculus (2.4%), 18 Rattus flavipectus (1.7%) and 15 Smelly shrew (density 1.4%). 1 Smelly shrew was tested positive for orientia tsutsugamushi nucleic acid, and the negative results were found in the other rodent specimens. 27 Chigge mites were collected by small blackboard method and the density of mites was 0.12 for each blackboard, among which 3 larvae and 24 nymphs were found. 33 Chigger mites were collected from the ears of 3 Smelly shrew, and the density of the mite was 11 per mouse. All the captured Chigger mites were identified as Leptotrombidium scutellare and 1 group of specimens of Chigger mites from the external environment were positive for orientia tsutsugamushi nucleic acid. Conclusion: There was a high density of mice in the epidemic area from May to November and the species of the chigger mites were Chigger mites in Taizhou. The nucleic acid of the oriental tsutsugamushi was detected in the patients with acute scrub typhus, rodents and vectors. According to the above-mentioned results, it was considered that the scrub typhus epidemic area of Taizhou city has the natural foci of scrub typhus.

Neighbor-directed histidine N (τ)-alkylation: A route to imidazolium-containing phosphopeptide macrocycles

Our recently discovered, selective, on-resin route to N(τ)-alkylated imidazolium-containing histidine residues affords new strategies for peptide mimetic design. In this, we demonstrate the use of this chemistry to prepare a series of macrocyclic phosphopeptides, in which imidazolium groups serve as ring-forming junctions. Interestingly, these cationic moieties subsequently serve to charge-mask the phosphoamino acid group that directed their formation. Neighbor-directed histidine N(τ)-alkylation opens the door to new families of phosphopeptidomimetics for use in a range of chemical biology contexts.

Mitsunobu mischief: neighbor-directed histidine N(τ)-alkylation provides access to peptides containing selectively functionalized imidazolium heterocycles

There are few methodologies that yield peptides containing His residues with selective N(τ), N(π)-bis-alkylated imidazole rings. We have found that, under certain conditions, on-resin Mitsunobu coupling of alcohols with peptides having a N(π)-alkylated His residue results in selective and high-yield alkylation of the imidazole N(τ) nitrogen. The reaction requires the presence of a proximal phosphoric, carboxylic or sulfonic acid, and proceeds through an apparent intramolecular mechanism involving Mitsunobu intermediates. These transformations have particular application to phosphopeptides, where "charge masking" of one phosphoryl anionic charge by the cationic histidine imidazolium ion is now possible. This chemistry opens selective access to peptides containing differentially functionalized imidazolium heterocycles, which provide access to new classes of peptides and peptide mimetics.

Mono-anionic phosphopeptides produced by unexpected histidine alkylation exhibit high Plk1 polo-box domain-binding affinities and enhanced antiproliferative effects in HeLa cells

Binding of polo-like kinase 1 (Plk1) polo-box domains (PBDs) to phosphothreonine (pThr)/phosphoserine (pSer)-containing sequences is critical for the proper function of Plk1. Although high-affinity synthetic pThr-containing peptides provide starting points for developing PBD-directed inhibitors, to date the efficacy of such peptides in whole cell assays has been poor. This potentially reflects limited cell membrane permeability arising, in part, from the di-anionic nature of the phosphoryl group or its mimetics. In our current article we report the unanticipated on-resin N(τ)-alkylation of histidine residues already bearing a N(π)- alkyl group. This resulted in cationic imidazolium-containing pThr peptides, several of which exhibit single-digit nanomolar PBD-binding affinities in extracellular assays and improved antimitotic efficacies in intact cells. We enhanced the cellular efficacies of these peptides further by applying bio-reversible pivaloyloxymethyl (POM) phosphoryl protection. New structural insights presented in our current study, including the potential utility of intramolecular charge masking, may be useful for the further development of PBD-binding peptides and peptide mimetics.

Design and synthesis of Fmoc-Thr[PO(OH)(OPOM)] for the preparation of peptide prodrugs containing phosphothreonine in fully protected form

The design and efficient synthesis of N-Fmoc-phosphothreonine protected by a mono-(pivaloyloxy)methyl (POM) moiety at its phosphoryl group (Fmoc-Thr[PO(OH)(OPOM)]-OH, 1, is reported. This reagent is suitable for solid-phase syntheses employing acid-labile resins and Fmoc-based protocols. It allows the preparation of phosphothreonine (pThr)-containing peptides bearing bis-POM-phosphoryl protection. The methodology allows the first reported synthesis of pThr-containing polypeptides having bioreversible prodrug protection, and as such it should be useful in a variety of biological applications.

Peptide-based inhibitors of Plk1 polo-box domain containing mono-anionic phosphothreonine esters and their pivaloyloxymethyl prodrugs

Binding of polo-like kinase 1 (Plk1) polo-box domains (PBDs) to phosphothreonine (pThr)/phosphoserine (pSer)-containing sequences is critical for the proper function of Plk1. Although high-affinity synthetic pThr-containing peptides may be used to disrupt PBD function, the efficacy of such peptides in whole cell assays has been poor. This potentially reflects limited cell membrane permeability arising in part from the di-anionic nature of the phosphoryl group. We report five-mer peptides containing mono-anionic pThr phosphoryl esters that exhibit single-digit nanomolar PBD binding affinities in extracellular assays and improved antimitotic efficacies in whole cell assays. The cellular efficacies of these peptides have been further enhanced by the application of bio-reversible pivaloyloxymethyl (POM) phosphoryl protection to a pThr-containing polypeptide. Our findings may redefine structural parameters for the development of PBD-binding peptides and peptide mimetics.

Design and synthesis of a reagent for solid-phase incorporation of the phosphothreonine mimetic (2S,3R)-2-amino-3-methyl-4-phosphonobutyric acid (Pmab) into peptides in a bio-reversible phosphonyl-bis-pivaloyloxymethyl (POM) prodrug form

Reported herein are the synthesis and solid-phase peptide incorporation of N-Fmoc-(2S,3R)-2-amino-3-methyl-4-phosphonobutyric acid bis-pivaloyloxymethyl phosphoryl ester [Fmoc-Pmab(POM)2-OH, 2] as a phosphatase-stable phosphothreonine (pThr) mimetic bearing orthogonal protection suitable for the synthesis of Pmab-containing peptides having bio-reversible protection of the phosphonic acid moiety. This represents the first report of a bio-reversibly protected pThr mimetic in a form suitable for facile solid-phase peptide synthesis.

Non-proteinogenic amino acids in the pThr-2 position of a pentamer peptide that confer high binding affinity for the polo box domain (PBD) of polo-like kinase 1 (Plk1)

We report herein that incorporating long-chain alkylphenyl-containing non-proteinogenic amino acids in place of His at the pT-2 position of the parent polo-like kinase 1 (Plk1) polo box domain (PBD)-binding pentapeptide, PLHSpT (1a) increases affinity. For certain analogs, approximately two orders-of-magnitude improvement in affinity was observed. Although, none of the new analogs was as potent as our previously described peptide 1b, in which the pT-2 histidine imidazole ring is alkylated at its π nitrogen (N3), our current finding that the isomeric His(N1)-analog (1c) binds with approximately 50-fold less affinity than 1b, indicates the positional importance of attachment to the His imidazole ring. Our demonstration that a range of modified residues at the pT-2 position can enhance binding affinity, should facilitate the development of minimally-sized Plk1 PBD-binding antagonists.

Peptoid-Peptide hybrid ligands targeting the polo box domain of polo-like kinase 1

We replaced the amino terminal Pro residue of the Plk1 polo-box-domain-binding pentapeptide (PLHSpT) with a library of N-alkyl-Gly "peptoids", and identified long-chain tethered phenyl moieties giving greater than two-orders-of-magnitude affinity enhancement. Further simplification by replacing the peptoid residue with appropriate amides gave low-nanomolar affinity N-acylated tetrapeptides. Binding of the N-terminal long-chain phenyl extension was demonstrated by X-ray co-crystal data.

Identification of high affinity polo-like kinase 1 (Plk1) polo-box domain binding peptides using oxime-based diversification

In an effort to develop improved binding antagonists of the polo-like kinase 1 (Plk1) polo-box domain (PBD), we optimized interactions of the known high affinity 5-mer peptide PLHSpT using oxime-based post solid-phase peptide diversification of the N-terminal Pro residue. This allowed us to achieve up to two orders of magnitude potency enhancement. An X-ray crystal structure of the highest affinity analogue in complex with Plk1 PBD revealed new binding interactions in a hydrophobic channel that had been occluded in X-ray structures of the unliganded protein. This study represents an important example where amino acid modification by post solid-phase oxime ligation can facilitate the development of protein-protein interaction inhibitors by identifying new binding pockets that would not otherwise be accessible to coded amino acid residues.

Serendipitous alkylation of a Plk1 ligand uncovers a new binding channel

We obtained unanticipated synthetic byproducts from alkylation of the δ(1) nitrogen (N3) of the histidine imidazole ring of the polo-like kinase-1 (Plk1) polo-box domain (PBD)-binding peptide PLHSpT. For the highest-affinity byproduct, bearing a C(6)H(5)(CH(2))(8)- group, a Plk1 PBD cocrystal structure revealed a new binding channel that had previously been occluded. An N-terminal PEGylated version of this peptide containing a hydrolytically stable phosphothreonyl residue (pT) bound the Plk1 PBD with affinity equal to that of the non-PEGylated parent but showed markedly less interaction with the PBDs of the two closely related proteins Plk2 and Plk3. Treatment of cultured cells with this PEGylated peptide resulted in delocalization of Plk1 from centrosomes and kinetochores and in chromosome misalignment that effectively induced mitotic block and apoptotic cell death. This work provides insights that might advance efforts to develop Plk1 PBD-binding inhibitors as potential Plk1-specific anticancer agents.

Spatial organization of Ca(2+) entry and exocytosis in mouse pancreatic beta-cells

Secretion from single pancreatic beta-cells was imaged using a novel technique in which Zn(2+), costored in secretory granules with insulin, was detected by confocal fluorescence microscopy as it was released from the cells. Using this technique, it was observed that secretion from beta-cells was limited to an active region that comprised approximately 50% of the cell perimeter. Using ratiometric imaging with indo-1, localized increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) evoked by membrane depolarization were also observed. Using sequential measurements of secretion and [Ca(2+)](i) at single cells, colocalization of exocytotic release sites and Ca(2+) entry was observed when cells were stimulated by glucose or K(+). Treatment of cells with the Ca(2+) ionophore 4-Br-A23187 induced large Ca(2+) influx around the entire cell circumference. Despite the nonlocalized increase in [Ca(2+)](i), secretion evoked by 4-Br-A23187 was still localized to the same region as that evoked by secretagogues such as glucose. It is concluded that Ca(2+) channels activated by depolarization are localized to specific membrane domains where exocytotic release also occurs; however, localized secretion is not exclusively regulated by localized increases in [Ca(2+)](i), but instead involves spatial localization of other components of the exocytotic machinery.

[Study on mitoxantrone albumin microspheres for liver targeting]

An optimum procedure was established for preparing mitoxantrone albumin microspheres (DHAQ-BSA-MS) with emulsion-heating solidification. The morphology, diameters, drug loading, release characteristics, stability and its distribution in vivo of the drug-loaded albumin microspheres were studied. The results showed that the surface was regular, the average diameter was 0.99 micron, mean surface diameter was 1.24 microns and mean volume diameter was 1.44 microns, apparent drug loading was 2.558 +/- 0.101 micrograms.mg-1 (n = 5), effective drug loading was 1.503% +/- 0.127% (n = 5), embedding ratio was 92.82% +/- 6.48% (n = 5), and the release characteristics were in accord with "biphase kinetics equation": 1 - Q = 0.6428e-0.2132t + 0.3988e-0.00150t (gamma 1 = -0.9951, gamma 2 = -0.9982); T1/2 alpha = 3.250 h, T1/2 beta = 461.7 h. The stability of the drug-loaded albumin microspheres was good after three months storage at room temperature. The results determined by HPLC showed that the drug accumulated about 77.6% +/- 1.38% of the dose in the liver 20 minutes after intravenous injection to mice. This indicates that DHAQ-BSA-MS showed remarkable targeting for liver, and it seems to have important value for increasing the antihepatoma effect and decreasing the toxicity of mitoxantrone.

Roles of insulin receptor substrate-1, phosphatidylinositol 3-kinase, and release of intracellular Ca2+ stores in insulin-stimulated insulin secretion in beta -cells

The signaling pathway by which insulin stimulates insulin secretion and increases in intracellular free Ca(2+) concentration ([Ca(2+)](i)) in isolated mouse pancreatic beta-cells and clonal beta-cells was investigated. Application of insulin to single beta-cells resulted in increases in [Ca(2+)](i) that were of lower magnitude, slower onset, and longer lifetime than that observed with stimulation with tolbutamide. Furthermore, the increases in [Ca(2+)](i) originated from interior regions of the cell rather than from the plasma membrane as with depolarizing stimuli. The insulin-induced [Ca(2+)](i) changes and insulin secretion at single beta-cells were abolished by treatment with 100 nm wortmannin or 1 micrometer thapsigargin; however, they were unaffected by 10 micrometer U73122, 20 micrometer nifedipine, or removal of Ca(2+) from the medium. Insulin-stimulated insulin secretion was also abolished by treatment with 2 micrometer bisindolylmaleimide I, but [Ca(2+)](i) changes were unaffected. In an insulin receptor substrate-1 gene disrupted beta-cell tumor line, insulin did not evoke either [Ca(2+)](i) changes or insulin secretion. The data suggest that autocrine-activated increases in [Ca(2+)](i) are due to release of intracellular Ca(2+) stores, especially the endoplasmic reticulum, mediated by insulin receptor substrate-1 and phosphatidylinositol 3-kinase. Autocrine activation of insulin secretion is mediated by the increase in [Ca(2+)](i) and activation of protein kinase C.

Correlated oscillations in glucose consumption, oxygen consumption, and intracellular free Ca(2+) in single islets of Langerhans

Micron-sized sensors were used to monitor glucose and oxygen levels in the extracellular space of single islets of Langerhans in real-time. At 10 mM glucose, oscillations in intraislet glucose concentration were readily detected. Changes in glucose level correspond to changes in glucose consumption by glycolysis balanced by mass transport into the islet. Oscillations had a period of 3.1 +/- 0.2 min and amplitude of 0.8 +/- 0.1 mM glucose (n = 21). Superimposed on these oscillations were faster fluctuations in glucose level during the periods of low glucose consumption. Oxygen level oscillations that were out of phase with the glucose oscillations were also detected. Oscillations in both oxygen and glucose consumption were strongly dependent upon extracellular Ca(2+) and sensitive to nifedipine. Simultaneous measurements of glucose with intracellular Ca(2+) ([Ca(2+)](i)) revealed that decreases in [Ca(2+)](i) preceded increases in glucose consumption by 7.4 +/- 2.1 s during an oscillation (n = 9). Conversely, increases in [Ca(2+)](i) preceded increases in oxygen consumption by 1.5 +/- 0.2 s (n = 4). These results suggest that during oscillations, bursts of glycolysis begin after Ca(2+) has stopped entering the cell. Glycolysis stimulates further Ca(2+) entry, which in turn stimulates increases in respiration. The data during oscillation are in contrast to the time course of events during initial exposure to glucose. Under these conditions, a burst of oxygen consumption precedes the initial rise in [Ca(2+)](i). A model to explain these results is described.

Detection of secretion from single pancreatic beta-cells using extracellular fluorogenic reactions and confocal fluorescence microscopy

Confocal microscopy with Zinquin, a fluorogenic Zn(2+)-specific indicator, was used for spatially and temporally resolved measurement of Zn2+ efflux from single pancreatic beta-cells. When cells were incubated in buffer containing Zinquin, application of insulin secretagogues evoked an increase in fluorescence around the surface of the cell, indicative of detection of Zn2+ efflux from the cell. The fluorescence increases corresponded spatially and temporally with measurements of exocytosis obtained simultaneously by amperometry. When images were taken at 266-ms intervals, the detection limit for Zn2+ was approximately 0.5 microM. With this image frequency, it was possible to observe bursts of fluorescence which were interpreted as fluctuations of Zn2+ level due to exocytosis. The average intensity of these fluorescence bursts corresponded to a Zn2+ concentration of approximately 7 microM. Since insulin is co-stored with Zn2+ in secretory vesicles, it was concluded that the Zn2+ efflux corresponded to exocytosis of insulin/Zn(2+)-containing granules from the beta-cell. Exocytosis sites identified by this technique were frequently localized to one portion of the cell, indicative of active areas of release.