Identification of sitagliptin binding proteins by affinity purification mass spectrometry.

Type 2 diabetes mellitus (T2DM) is recognized as a serious public health concern with increasing incidence. The dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin has been used for the treatment of T2DM worldwide. Although sitagliptin has excellent therapeutic outcome, adverse effects are observed. In addition, previous studies have suggested that sitagliptin may have pleiotropic effects other than treating T2DM. These pieces of evidence point to the importance of further investigation of the molecular mechanisms of sitagliptin, starting from the identification of sitagliptin-binding proteins. In this study, by combining affinity purification mass spectrometry (AP-MS) and stable isotope labeling by amino acids in cell culture (SILAC), we discover seven high-confidence targets that can interact with sitagliptin. Surface plasmon resonance (SPR) assay confirms the binding of sitagliptin to three proteins, i. e., LYPLAL1, TCP1, and CCAR2, with binding affinities (K D) ranging from 50.1 µM to 1490 µM. Molecular docking followed by molecular dynamic (MD) simulation reveals hydrogen binding between sitagliptin and the catalytic triad of LYPLAL1, and also between sitagliptin and the P-loop of ATP-binding pocket of TCP1. Molecular mechanics Poisson-Boltzmann Surface Area (MMPBSA) analysis indicates that sitagliptin can stably bind to LYPLAL1 and TCP1 in active sites, which may have an impact on the functions of these proteins. SPR analysis validates the binding affinity of sitagliptin to TCP1 mutant D88A is ~10 times lower than that to the wild-type TCP1. Our findings provide insights into the sitagliptin-targets interplay and demonstrate the potential of sitagliptin in regulating gluconeogenesis and in anti-tumor drug development.

Systematic Identification of Mycobacterium tuberculosis Effectors Reveals that BfrB Suppresses Innate Immunity.

Mycobacterium tuberculosis (Mtb) has evolved multiple strategies to counter the human immune system. The effectors of Mtb play important roles in the interactions with the host. However, because of the lack of highly efficient strategies, there are only a handful of known Mtb effectors, thus hampering our understanding of Mtb pathogenesis. In this study, we probed Mtb proteome microarray with biotinylated whole-cell lysates of human macrophages, identifying 26 Mtb membrane proteins and secreted proteins that bind to macrophage proteins. Combining GST pull-down with mass spectroscopy then enabled the specific identification of all binders. We refer to this proteome microarray-based strategy as SOPHIE (Systematic unlOcking of Pathogen and Host Interacting Effectors). Detailed investigation of a novel effector identified here, the iron storage protein BfrB (Rv3841), revealed that BfrB inhibits NF-κB-dependent transcription through binding and reducing the nuclear abundance of the ribosomal protein S3 (RPS3), which is a functional subunit of NF- κB. The importance of this interaction was evidenced by the promotion of survival in macrophages of the mycobacteria, Mycobacterium smegmatis, by overexpression of BfrB. Thus, beyond demonstrating the power of SOPHIE in the discovery of novel effectors of human pathogens, we expect that the set of Mtb effectors identified in this work will greatly facilitate the understanding of the pathogenesis of Mtb, possibly leading to additional potential molecular targets in the battle against tuberculosis.

The Ser/Thr Protein Kinase Protein-Protein Interaction Map of M. tuberculosis.

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis, the leading cause of death among all infectious diseases. There are 11 eukaryotic-like serine/threonine protein kinases (STPKs) in Mtb, which are thought to play pivotal roles in cell growth, signal transduction and pathogenesis. However, their underlying mechanisms of action remain largely uncharacterized. In this study, using a Mtb proteome microarray, we have globally identified the binding proteins in Mtb for all of the STPKs, and constructed the first STPK protein interaction (KPI) map that includes 492 binding proteins and 1,027 interactions. Bioinformatics analysis showed that the interacting proteins reflect diverse functions, including roles in two-component system, transcription, protein degradation, and cell wall integrity. Functional investigations confirmed that PknG regulates cell wall integrity through key components of peptidoglycan (PG) biosynthesis, e.g. MurC. The global STPK-KPIs network constructed here is expected to serve as a rich resource for understanding the key signaling pathways in Mtb, thus facilitating drug development and effective control of Mtb.

RecJ-like protein from Pyrococcus furiosus has 3'-5' exonuclease activity on RNA: implications for proofreading of 3'-mismatched RNA primers in DNA replication.

Replicative DNA polymerases require an RNA primer for leading and lagging strand DNA synthesis, and primase is responsible for the de novo synthesis of this RNA primer. However, the archaeal primase from Pyrococcus furiosus (Pfu) frequently incorporates mismatched nucleoside monophosphate, which stops RNA synthesis. Pfu DNA polymerase (PolB) cannot elongate the resulting 3'-mismatched RNA primer because it cannot remove the 3'-mismatched ribonucleotide. This study demonstrates the potential role of a RecJ-like protein from P. furiosus (PfRecJ) in proofreading 3'-mismatched ribonucleotides. PfRecJ hydrolyzes single-stranded RNA and the RNA strand of RNA/DNA hybrids in the 3'-5' direction, and the kinetic parameters (Km and Kcat) of PfRecJ during RNA strand digestion are consistent with a role in proofreading 3'-mismatched RNA primers. Replication protein A, the single-stranded DNA-binding protein, stimulates the removal of 3'-mismatched ribonucleotides of the RNA strand in RNA/DNA hybrids, and Pfu DNA polymerase can extend the 3'-mismatched RNA primer after the 3'-mismatched ribonucleotide is removed by PfRecJ. Finally, we reconstituted the primer-proofreading reaction of a 3'-mismatched ribonucleotide RNA/DNA hybrid using PfRecJ, replication protein A, Proliferating cell nuclear antigen (PCNA) and PolB. Given that PfRecJ is associated with the GINS complex, a central nexus in archaeal DNA replication fork, we speculate that PfRecJ proofreads the RNA primer in vivo.

Specific pupylation as IDEntity reporter (SPIDER) for the identification of protein-biomolecule interactions.

Protein-biomolecule interactions play pivotal roles in almost all biological processes. For a biomolecule of interest, the identification of the interacting protein(s) is essential. For this need, although many assays are available, highly robust and reliable methods are always desired. By combining a substrate-based proximity labeling activity from the pupylation pathway of Mycobacterium tuberculosis and the streptavidin (SA)-biotin system, we developed the Specific Pupylation as IDEntity Reporter (SPIDER) method for identifying protein-biomolecule interactions. Using SPIDER, we validated the interactions between the known binding proteins of protein, DNA, RNA, and small molecule. We successfully applied SPIDER to construct the global protein interactome for m6A and mRNA, identified a variety of uncharacterized m6A binding proteins, and validated SRSF7 as a potential m6A reader. We globally identified the binding proteins for lenalidomide and CobB. Moreover, we identified SARS-CoV-2-specific receptors on the cell membrane. Overall, SPIDER is powerful and highly accessible for the study of protein-biomolecule interactions.

Enhancing separation of histidine from amino acids via free-flow affinity electrophoresis with gravity-induced uniform hydrodynamic flow.

In this paper, a novel mode of free-flow affinity electrophoresis (FFAE) was developed to indirectly enhance the separation of free-flow electrophoresis (FFE). In the mode of FFAE, a Ni(II) with high electric charge density and histidine (His) is chosen as a model ligand and target solute, respectively. Through the controlling of experimental conditions (10 mM pH 6.0 Na(2)HPO(4)-NaH(2)PO(4) with 2.0 mM NiCl(2)·6H(2)O background buffer), Ni(II) can combine with His and the combination leads to the high electric charge density of affinity complex of His-Ni(II) in contrast to the low density of free His molecule. But the ligand has weak interaction with uninterested amino acids. Thus, the mobility of His existing as His-Ni(II) is greatly increased from 14.5×10(-8) m(2) V(-1) s(-1) to 30.2 × 10(-8) m(2) V(-1) s(-1), while those mobilities of uninterested amino acids are almost constant. By virtue of the mode, we developed the FFAE procedure and conducted the relevant experiments. The experiments demonstrated the following merits of the FFAE technique: (i) clear enhancement of separation between the target solute of His and uninterested amino acids; (ii) simplicity, and (iii) low cost. Furthermore, the technique was used for the continuous separation of His from its complex sample, and the purity of His was near to 100%. All of the results demonstrate the feasibility of affinity separation in FFE. The developed FFAE may be used in the separation and pretreatment of some biological molecules (e.g. peptides).

Glycyrrhizin attenuates rat ischemic spinal cord injury by suppressing inflammatory cytokines and HMGB1.

AIM: To investigate the neuroprotective effect of glycyrrhizin (Gly) against the ischemic injury of rat spinal cord and the possible role of the nuclear protein high-mobility group box 1 (HMGB1) in the process. METHODS: Male Sprague-Dawley rats were subjected to 45 min aortic occlusion to induce transient lumbar spinal cord ischemia. The motor functions of the animals were assessed according to the modified Tarlov scale. The animals were sacrificed 72 h after reperfusion and the lumbar spinal cord segment (L2-L4) was taken out for histopathological examination and Western blotting analysis. Serum inflammatory cytokine and HMGB1 levels were analyzed using ELISA. RESULTS: Gly (6 mg/kg) administered intravenously 30 min before inducing the transient lumbar spinal cord ischemia significantly improved the hind-limb motor function scores, and reduced the number of apoptotic neurons, which was accompanied by reduced levels of tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß) and interleukin-6 (IL-6) in the plasma and injured spinal cord. Moreover, the serum HMGB1 level correlated well with the serum TNF-α, IL-1ß and IL-6 levels during the time period of reperfusion. CONCLUSION: The results suggest that Gly can attenuate the transient spinal cord ischemic injury in rats via reducing inflammatory cytokines and inhibiting the release of HMGB1.

A novel single nucleotide polymorphism detection of a double-stranded DNA target by a ribonucleotide-carrying molecular beacon and thermostable RNase HII.

Single nucleotide polymorphisms (SNPs) are the most abundant form of genetic variation. SNPs are important markers that link sequence variations to phenotypic changes. Because of the importance of SNPs in the life and medical sciences, a great deal of effort has been devoted to developing accurate, rapid, and cost-effective technologies for SNP analysis. In this article, we describe a novel method for SNP genotyping based on differential fluorescence emission due to cleavage by Thermus thermophilus RNase HII (TthRNase HII) of DNA heteroduplexes containing an SNP site-specific chimeric DNA-rN(1)-DNA molecular beacon (cMB). We constructed a loop sequence for a cMB that contains a single SNP-specific ribonucleotide at the central site. When the cMB probe is hybridized to a target double-stranded DNA (dsDNA), a perfect match of the cMB/DNA duplex permits efficient cleavage with TthRNase HII, whereas a mismatch in the duplex due to an SNP greatly reduces efficiency. Cleavage efficiency is measured by the incremental difference of fluorescence emission of the beacon. We show that the genotypes of 10 individuals at 12 SNP sites across a series of human leukocyte antigen (HLA) can be determined correctly with respect to conventional DNA sequencing. This novel TthRNase HII-based method offers a platform for easy and accurate SNP analysis.

Expression and characterization of thymine-DNA glycosylase from Aeropyrum pernix.

The recombinant thymine-DNA glycosylase (TDG) from Aeropyrum pernix (A. pernix) was expressed in Escherichia coli. The enzymatic activity of recombinant A. pernix TDG (ApeTDG) was characterized using oligonucleotides containing a thymine/uracil base as substrate. ApeTDG had distinct glycosylase activity on T/G mismatch. The optimal temperature and pH for thymine removal were 65-70 degrees C and pH 7.0-8.5, respectively. High concentration of NaCl inhibited the thymine removal. Divalent ions had different influence on the thymine removal by ApeTDG. Ca(2+) and Mg(2+) had no inhibition on the enzymic activity, but Ni(2+), Co(2+), Cu(2+), Mn(2+), and Zn(2+) completely inhibited the excision reaction. As derived from a hyperthermophilic archaea, ApeTDG protein was heat-resistant at 75 degrees C. ApeTDG also had a relatively weak DNA glycosylase activity on uracil base, with the following order: U/C>U/G approximately U/T>U/U approximately U/I approximately U/AP approximately U/->U/A. Additional mismatch located at 3' of T/G had less inhibition on the thymine removal than that located at 5' of T/G, and two additional mismatches located at each side of T/G completely inhibited the excision of thymine. Together, these data suggest that ApeTDG is a TDG protein with weak UDG activity.

iTRAQ-based quantitative proteomic analysis of Pseudomonas aeruginosa SJTD-1: A global response to n-octadecane induced stress.

N-octadecane, the shortest solid-state alkane, was efficiently consumed by Pseudomonas aeruginosa SJTD-1. To reveal its mechanism, the iTRAQ-LC-MS/MS strategy was applied for quantification of proteins in response to alkane. As a result, 383 alkane-responsive proteins were identified and these proteins could be linked to multiple biochemical pathways. Above all, the level of alkane hydroxylase AlkB2 has been significantly higher in alkane condition. Also, the presence of a putative novel AlmA-like monooxygenase and its role on alkane hydroxylation were firstly proposed in Pseudomonas. In addition, other proteins for chemotaxic, ß-oxidation, glyoxylate bypass, alkane uptake, cross membrane transport, enzymatic steps and the carbon flow may have important roles in the cellular response to alkane. Most of those differently expressed proteins were functionally mapped into pathways of alkane degradation or metabolism thereof. In this sense, findings in this study provide critical clues to reveal biodegradation of long chain n-alkanes and rationally be important for potent biocatalyst for bioremediation in future. BIOLOGICAL SIGNIFICANCE: We use iTRAQ strategy firstly to compare the proteomes of Pseudomonas SJTD-1 degrading alkane. Changes in protein clearly provide a comprehensive overview on alkane hydroxylation of SJTD-1, including those proteins for chemotaxis, alkane uptake, cross membrane transport, enzymatic steps and the carbon flow. AlkB2 and a putative novel AlmA-like monooxygenase have been highlighted for their outstanding contribution to alkane use. We found that several chemotaxic proteins were altered in abundance in alkane-grown cells. These results may be helpful for understanding alkane use for Pseudomonas.

Effects of lidocaine on cerebral oxygen supply-consumption balance and hemodynamics during anesthesia induction in patients with supratentorial tumor.

OBJECTIVE: To study the effects of lidocaine on the balance between cerebral oxygen supply-consumption and on the hemodynamics during anesthesia induction in patients with supratentorial tumor. METHODS: Twenty-four patients with supratentorial tumor were randomly divided into lidocaine group (n=12) and control group (n=12). Blood gas analysis and determinations of plasma lactic acid and glucose in the radial artery and internal jugular venous bulb were performed. Oxygen extraction ratio (OER) and blood oxygen content in the artery and internal jugular venous bulb were calculated during anesthesia induction. RESULTS: OER and difference declined in plasma lactic acid level between the internal jugular venous bulb and the artery, and blood oxygen saturation as well as blood oxygen pressure in the internal jugular venous bulb and the artery increased along with blood oxygen content in the internal jugular venous bulb in both groups during anesthesia induction. Comparison between the groups showed that only the changes in blood oxygen pressure in the internal jugular venous bulb were statistically significant. Changes in the hemodynamics in lidocaine group were less obvious than those in the control group during anesthesia induction. CONCLUSION: Lidocaine does not significantly influence cerebral oxygen balance and may effectively inhibit hemodynamic response during anesthesia induction in patients with supratentorial tumor.

Chlamydophila pneumoniae endonuclease IV prefers to remove mismatched 3' ribonucleotides: implication in proofreading mismatched 3'-terminal nucleotides in short-patch repair synthesis.

DNA polymerase I (DNApolI) catalyzes DNA synthesis during Okazaki fragment maturation, base excision repair, and nucleotide excision repair. Some bacterial DNApolIs are deficient in 3'-5' exonuclease, which is required for removing an incorrectly incorporated 3'-terminal nucleotide during DNA elongation by DNA polymerase activity. The key amino acid residues in the exonuclease center of Chlamydophila pneumoniae DNApolI (CpDNApolI) are naturally mutated, resulting in the loss of 3'-5' exonuclease. Hence, the manner by which CpDNApolI proofreads the incorrectly incorporated nucleotide during DNA synthesis warrants clarification. C. pneumoniae encodes three 3'-5' exonuclease activities: one endonuclease IV and two homologs of the epsilon subunit of replicative DNA polymerase III. The three proteins were biochemically characterized using single- and double-stranded DNA substrate. Among them, C. pneumoniae endonuclease IV (CpendoIV) possesses 3'-5' exonuclease activity that prefers to remove mismatched 3'-terminal nucleotides in the nick, gap, and 3' recess of a double-stranded DNA (dsDNA). Finally, we reconstituted the proofreading reaction of the mismatched 3'-terminal nucleotide using the dsDNA with a nick or 3' recess as substrate. Upon proofreading of the mismatched 3'-terminal nucleotide by CpendoIV, CpDNApolI can correctly reincorporate the matched nucleotide and the nick is further sealed by DNA ligase. Based on our biochemical results, we proposed that CpendoIV was responsible for proofreading the replication errors of CpDNApolI.

[Effects of different intraabdominal pressure of carbon dioxide pneumoperitoneum on hemorrheology and microcirculation in rabbits].

OBJECTIVE: To study effects of different intraabdominal pressure of carbon dioxide (Cq2) pneumoperitoneum on hemorrheology and microcirculation in rabbits. METHODS: Eighteen female healthy rabbits weighing 2.2 kg to 3.5 kg were randomly divided into three groups equally based on pneumoperitoneum pressure: 0 mmHg group (group I),10 mmHg group (group II) and 15 mmHg (group III). Each group received 1 h pneumoperitoneum under different pressure. Blood samples were taken at 5 min before CO2 pneumoperitoneum, at 30 and 60 min after pneumoperitoneum for the measurements of indexes of hemorrheology. Hemodynamics including heart rate (HR), mean arterial pressure (MAP) and the volume and velocity of the microcirculation of auricle were continuously monitored, such indexes were recorded at the related time. RESULTS: Afer pneumoperitoneum at 30 and 60 min, compared with group I, HR, MAP, the whole blood viscosity, the aggregation and rigid indexes of RBC were significantly raised in group II (P < 0.05), the deformability indexes of RBC, the volume and velocity of the microcirculation were markedly decreased (P < 0.05). Even more significant changes were observed in group III (P < 0.01). The plasma viscosity and the hematocrit changed little. CONCLUSION: After CO2 pneumoperitoneum, hemorrheology is decreased; Although HR, MAP are raised, the volume and velocity of the microcirculation are decreased.

The histone deacetylase inhibitor suberoylanilide hydroxamic acid induces growth inhibition and enhances taxol-induced cell death in breast cancer.

PURPOSE: The histone deacetylase inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA) enhances taxol-induced antitumor effects against some human cancer cells. The aim of this study is to investigate whether SAHA can enhance taxol-induced cell death against human breast cancer cells and to illustrate the mechanism in detail. METHODS: A panel of eight human breast cancer cell lines and an immortalized human breast epithelial cell line were used to determine the inhibitory effects of SAHA, taxol, or their combination by MTT assay. The effects of SAHA with or without taxol on cell cycle distributions, apoptosis, and protein expressions were also examined. The inhibitory effects on tumor growth were characterized in vivo in BALB/c nude mice bearing a breast cancer xenograft model. RESULTS: Taxol-resistant and multi-resistant breast cancer cells were as sensitive to SAHA as taxol-sensitive breast cancer cells. A dose-dependent synergistic growth inhibition was found in all the tested breast cancer cell lines treated with the SAHA/taxol combinations. The synergetic effect was also observed in the in vivo xenograft tumor model. The cell cycle analysis and apoptosis assay showed that the synergistic effects resulted from enhanced G2/M arrest and apoptosis. CONCLUSIONS: SAHA increased the anti-tumor effects of taxol in breast cancer in vitro and in vivo. The combination of SAHA and taxol may have therapeutic potential in the treatment of breast cancer.