Aspartate isomerization in the complementarity-determining regions of two closely related monoclonal antibodies

The aspartic acid residues (Asp) present in the complementarity-determining regions (CDRs) of the light chains of two recombinant monoclonal antibodies (MAbs), MAb I and MAb II, are highly susceptible to isomerization due to the presence of glycine residues (Gly) on their C-terminal ends. Asp isomerization in these MAbs leads to formation of the isoaspartate (IsoAsp) and the cyclic imide (Asu) variants of these MAbs. Both MAb I and MAb II, employed in this study, elicit their pharmacological responses through binding human IgE. The formation of the MAb variants as a result of Asp isomerization significantly reduces the binding affinities of these antibodies to IgE, thereby reducing their potencies. Here we report on significant differences in the susceptibility of the MAb I and the MAb II to Asp isomerization. The molecular basis for these differences in rates of Asp isomerization was elucidated. The effect of primary sequence on Asp isomerization was evaluated using pentapeptide models of the MAbs, which included the labile Asp residues and their neighboring amino acid residues. The separation of the parent MAbs and pentapeptides from their isomerization products was achieved using hydrophobic interaction chromatography (HIC) and rp-HPLC, respectively. Structural characterization of the MAbs was performed using differential scanning calorimetry (DSC), circular dichroism (CD), and X-ray crystallography. Our investigations demonstrate that the differences in the Asp isomerization rates between MAb I and MAb II can be attributed to structural factors including the conformational flexibility and the extent of solvent exposure of the labile Asp residue.     

Impact of orientation and flexibility of peptide linkers on <Emphasis Type="Italic">T. maritima</Emphasis> lipase Tm1350 displayed on <Emphasis Type="Italic">Bacillus subtilis</Emphasis> spores surface using CotB as fusion partner

Fusion protein construction often requires peptide linkers for prolonged conformation, extended stability and enzyme activity. In this study a series of fusion between Thermotoga maritima lipase Tm1350 and Bacillus subtillis coat protein CotB, comprising of several peptide linkers, with different length, flexibility and orientations were constructed. Effects of temperature, pH and chemicals were examined, on the activity of displayed enzyme. The fusion protein with longer flexible linkers L9 [(GGGGS)₄] and L7 (GGGGS-GGGGS-EAAAK-EAAAK-GGGGS-GGGGS) possess 1.29 and 1.16-fold higher activity than the original, under optimum temperature and pH respectively. Moreover, spore surface displaying Tm1350 with L3 (EAAAK-GGGGS) and L9 ((GGGGS)₄) showed extended thermostably, maintaining 1.40 and 1.35-fold higher activity than the original respectively, at 80 °C after 5 h of incubation. The enzyme activity of linkers with different orientation, including L5, L6 and L7 was determined, where L7 maintained 1.05 and 1.27-fold higher activity than L5 and L6. Effect of 0.1% proteinase K, bromelain, 20% ethanol and 30% methanol was investigated. Linkers with appropriate Glycine residues (flexible) showed higher activity than Alanine residues (rigid). The activity of the displayed enzyme can be improved by maintaining orientation and flexibility of peptide linkers, to evaluate high activity and stability in industrial processes.     

Proteome analysis on differentially expressed proteins of the fat body of two silkworm breeds, Bombyx mori, exposed to heat shock exposure

Proteomes of heat tolerant (multivoltine) and heat susceptible (bivoltine) silkworms (Bombyx mori) in response to heat shock were studied. Detected proteins from fat body were identified by using MALDI-TOF/TOF spectrometer, MS/MS, and MS analysis. Eight proteins, including small heat shock proteins (sHSPs) and HSP70, were expressed similarly in both breeds, while 4 protein spots were expressed specifically in the bivoltine breed and 12 protein spots were expressed specifically in the multivoltine breed. In the present proteomics approach, 5 separate spots of sHSP proteins (HSP19.9, HSP20.1, HSP20.4, HSP20.8, and HSP21.4) were identified. Protein spot intensity of sHSPs was lower in the multivoltine breed than in the bivoltine breed after the 45°C heat shock treatment, while the difference between two breeds was not significant after the 41°C heat shock treatment. These results indicated that some other mechanisms might be engaged in thermal tolerance of multivotine breed except for the expression of sHSP and HSP70. There were visible differences in the intensity of heat shock protein expression between male and female, however, differences were not statistically significant.     

Identification of a Small Peptide That Inhibits PCSK9 Protein Binding to the Low Density Lipoprotein Receptor

PCSK9 (proprotein convertase subtilisin/kexin type 9) is a negative regulator of the hepatic LDL receptor, and clinical studies with PCSK9-inhibiting antibodies have demonstrated strong LDL-c-lowering effects. Here we screened phage-displayed peptide libraries and identified the 13-amino acid linear peptide Pep2-8 as the smallest PCSK9 inhibitor with a clearly defined mechanism of inhibition that has been described. Pep2-8 bound to PCSK9 with a K_D of 0.7 μm but did not bind to other proprotein convertases. It fully restored LDL receptor surface levels and LDL particle uptake in PCSK9-treated HepG2 cells. The crystal structure of Pep2-8 bound to C-terminally truncated PCSK9 at 1.85 Å resolution showed that the peptide adopted a strand-turn-helix conformation, which is remarkably similar to its solution structure determined by NMR. Consistent with the functional binding site identified by an Ala scan of PCSK9, the structural Pep2-8 contact region of about 400 Ų largely overlapped with that contacted by the EGF(A) domain of the LDL receptor, suggesting a competitive inhibition mechanism. Consistent with this, Pep2-8 inhibited LDL receptor and EGF(A) domain binding to PCSK9 with IC₅₀ values of 0.8 and 0.4 μm, respectively. Remarkably, Pep2-8 mimicked secondary structural elements of the EGF(A) domain that interact with PCSK9, notably the β-strand and a discontinuous short α-helix, and it engaged in the same β-sheet hydrogen bonds as EGF(A) does. Although Pep2-8 itself may not be amenable to therapeutic applications, this study demonstrates the feasibility of developing peptidic inhibitors to functionally relevant sites on PCSK9.     

PCR Detection of Salmonella enterica Serotype Montevideo in and on Raw Tomatoes Using Primers Derived from hilA

Salmonellae have been some of the most frequently reported etiological agents in fresh-produce-associated outbreaks of human infections in recent years. PCR assays using four innovative pairs of primers derived from hilA and sirA, positive regulators of Salmonella invasive genes, were developed to identify Salmonella enterica serotype Montevideo on and in tomatoes. Based on examination of 83 Salmonella strains and 22 non-Salmonella strains, we concluded that a pair of hilA primers detects Salmonella specifically. The detection limits of the PCR assay were 10¹ and 10⁰ CFU/ml after enrichment at 37°C for 6 and 9 h, respectively. When the assay was validated by detecting S. enterica serotype Montevideo in and on artificially inoculated tomatoes, 10² and 10¹ CFU/g were detected, respectively, after enrichment for 6 h at 37°C. Our results suggest that the hilA-based PCR assay is sensitive and specific, and can be used for rapid detection of Salmonellae in or on fresh produce.     

Oligomeric structure of the human asialoglycoprotein receptor: nature and stoichiometry of mutual complexes containing H1 and H2 polypeptides assessed by fluorescence photobleaching recovery

The interactions between H1 and H2, the two polypeptides comprising the human asialoglycoprotein receptor (ASGP-R), were investigated by immunofluorescence and lateral mobility measurements combined with antibody-mediated cross-linking and immobilization. Immunofluorescence microscopy revealed two ASGP-R populations on the cell surface, one homogeneously distributed and the other in micropatches. This was observed both in stably transfected NIH 3T3 lines expressing H1 and/or H2, and in the human hepatoma cell line HepG2. In transfected cells expressing both polypeptides (the 1-7-1 line), H1 and H2 were colocalized in the same micro aggregates. Moreover, enhancement of the patching of, e.g., H1 by IgG-mediated crosslinking was accompanied by copatching of H2. To quantify H1-H2 complex formation, the lateral diffusion of H1 and H2 was measured at 12 degrees C (to avoid internalization) by fluorescence photobleaching recovery. H1 (or H2) was immobilized by crosslinking with specific IgG molecules; the other chain was labeled with fluorescent monovalent Fab' fragments, and is lateral mobility was measured. In HepG2 cells, immobilization of either H1 or H2 led to an equal immobilization of the other, indicating that all the mobile H1 and H2 are in stable heterooligomers. In 1-7-1 cells, immobilization of H2 immobilized H1 to the same degree, but immobilization of H1 reduced the mobile fraction of H2 only by 2/3. Thus, in 1-7-1 cells all surface H1 molecules are associated with H2, but 1/3 of the H2 population is independent of H1. From these data and from measurements of the relative surface densities of H1 and H2, conclusions are drawn regarding the oligomeric structure and stoichiometry of the ASGP-R.     

Ambulatory Blood Pressure Monitoring in Individuals with HIV: A Systematic Review and Meta-Analysis

Introduction

Abnormal diurnal blood pressure (BP) rhythms may contribute to the high cardiovascular disease risk in HIV-positive (HIV⁺) individuals. To synthesize the current literature on ambulatory BP monitoring (ABPM) in HIV⁺ individuals, a systematic literature review and meta-analysis were performed.

Methods

Medical databases were searched through November 11, 2015 for studies that reported ABPM results in HIV⁺ individuals. Data were extracted by 2 reviewers and pooled differences between HIV⁺ and HIV-negative (HIV^-) individuals in clinic BP and ABPM measures were calculated using random-effects inverse variance weighted models.

Results

Of 597 abstracts reviewed, 8 studies with HIV⁺ cohorts met the inclusion criteria. The 420 HIV⁺ and 714 HIV^- individuals in 7 studies with HIV^- comparison groups were pooled for analyses. The pooled absolute nocturnal systolic and diastolic BP declines were 3.16% (95% confidence interval [CI]: 1.13%, 5.20%) and 2.92% (95% CI: 1.64%, 4.19%) less, respectively, in HIV⁺ versus HIV^- individuals. The pooled odds ratio for non-dipping systolic BP (nocturnal systolic BP decline <10%) in HIV⁺ versus HIV^- individuals was 2.72 (95% CI: 1.92, 3.85). Differences in mean clinic, 24-hour, daytime, or nighttime BP were not statistically significant. I² and heterogeneity chi-squared statistics indicated the presence of high heterogeneity for all outcomes except percent DBP dipping and non-dipping SBP pattern.

Conclusions

An abnormal diurnal BP pattern may be more common among HIV⁺ versus HIV^- individuals. However, results were heterogeneous for most BP measures, suggesting more research in this area is needed.     

Some characteristics of a vitamin K-dependent carboxylating system from rat liver microsomes

Vitamin K-dependent carboxylation of protein has been obtained in microsomes from K-deficient rats by supplementing the microsomes with either a reduced pyridine nucleotide or dithiothreitol. γ-Carboxyglutamate residues have been directly identified as the radioactive reaction product after incubating the microsomes with NaH¹⁴CO₃ and vitamin K. Evidence is presented that vitamin K is reduced to the hydroquinone prior to its involvement in carboxylation and that dithiothreitol has an additional role of protecting a critical sulfhydryl group. A structure-activity study using a variety of vitamins K and related compounds is reported.     

In vitro activity of mastoparan-AF alone and in combination with clinically used antibiotics against multiple-antibiotic-resistant Escherichia coli isolates from animals

The in vitro activity of mastoparan-AF, an amphipathic antimicrobial peptide isolated from the hornet venom of Vespa affinis, alone and in combination with various clinically used antibiotics, was investigated against 21 Escherichia coli isolates/strains. Most E. coli isolates tested were detected containing multiple-antimicrobial resistance genes. Antimicrobial activity of mastoparan-AF was measured by MIC, MBC, time-kill kinetic assay and chequerboard titration method. Mastoparan-AF exhibited potent antimicrobial activity against most multiple-antibiotic-resistant E. coli isolates at the concentrations ranging from 4 to 16 μg/ml. Combination studies showed that mastoparan-AF acts synergistically with certain antibiotics, i.e., cephalothin or gentamicin, against some multiple-antibiotic-resistant E. coli isolates. In conclusion, mastoparan-AF alone or in combination with other antibiotics could be promising as alternatives for combating multiple-antibiotic-resistant E. coli in future clinical applications.