[Changes in genotype prevalence of human papillomavirus over 10-year follow-up of a cervical cancer screening cohort]

Objective: To evaluate the dynamic variation of genotypes distribution of human papillomavirus (HPV) over 10-year follow-up in a cervical cancer screening cohort. Methods: Based on the Shanxi Province Cervical Cancer Screening Study Ⅰ cohort, we detected HPV genotypes on the well-preserved exfoliated cervical cells from women who were tested HPV positive from year 2005 to year 2014 using reverse linear probe hybridization assay. The changes of prevalence of type-specific HPV over time among the overall population were estimated using linear mixed models. The association between the type-specific HPV and cervical intraepithelial neoplasia grade 2 or worse (CIN2 +) was calculated by linear Chi-square test. Finally, the trends of multiple infections of HPV with the increase of the age were analyzed. Results: During the cervical cancer screening of the overall population from 2005 to 2014, the most common genotypes among the population were HPV16 and 52. The prevalence of HPV16 decreased over time from 4.6% in 2005 to 2.2% in 2010 and 2014 (F=8.125, P<0.001). The prevalence of HPV52 remained pretty stable and HPV33, 51 and 58 slightly decreased then apparently increased. Further stratification analysis by pathological lesions showed the same trend of the HPV prevalence for the histology normal women with the overall population. Of note, for those women with the cervical intraepithelial neoplasia (CIN2 +), the detection rate of HPV16 decreased from 65.22% in 2005 to 41.03% in 2010 and finally to 31.58% in 2014 (χ(2)=4.420, P=0.036) and that of HPV33 substantially increased. No significant variation was found for other types of HPV. Multiple infection rate varied with the growing age of the women. Conclusions: The genotypes prevalence of HPV tended to vary over time during cervical cancer screening in the context of regular screening combining with immediate treatment for those CIN2 + women. HPV16 prevalence significantly decreased over time, which indicated that the variation of type-specific HPV prevalence should be considered when regular cervical cancer screening was organized using HPV technique.

Phosphopeptide/phosphoprotein mapping by electron capture dissociation mass spectrometry

Of methods for dissociation of multiply charged peptide and protein ions, electron capture dissociation (ECD) has the advantages of cleaving between a high proportion of amino acids, without loss of such posttranslational modifications as glycosylation and carboxylation. Here this capability is successfully extended to phosphorylation, for which collisionally activated dissociation (CAD) can cause extensive loss of H3PO4 and HPO3. As shown here, these losses are minimal in ECD spectra, an advantage for measuring the degree of phosphorylation. For phosphorylated peptides, ECD and CAD spectra give complementary backbone cleavages for identifying modification sites. For a 24-kDa heterogeneous phosphoprotein, bovine beta-casein, activated ion ECD cleaved 87 of 208 backbone bonds that identified a phosphorylation site at Ser-15, and localized three more among Ser-17,-18, -19, and -22 and Thr-24, and the last among four other sites. This is the first direct site-specific characterization of this key post-translational modification on a protein without its prior degradation, such as proteolysis.

Counting individual sulfur atoms in a protein by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry: experimental resolution of isotopic fine structure in proteins

A typical molecular ion mass spectrum consists of a sum of signals from species of various possible isotopic compositions. Only the monoisotopic peak (e.g., all carbons are 12C; all nitrogens are 14N, etc.) has a unique elemental composition. Every other isotope peak at approximately integer multiples of approximately 1 Da higher in nominal mass represents a sum of contributions from isotope combinations differing by a few mDa (e.g., two 13C vs. two 15N vs. one 13C and one 15N vs. 34S, vs. 18O, etc., at approximately 2 Da higher in mass than the monoisotopic mass). At sufficiently high mass resolving power, each of these nominal-mass peaks resolves into its isotopic fine structure. Here, we report resolution of the isotopic fine structure of proteins up to 15.8 kDa (isotopic 13C,15N doubly depleted tumor suppressor protein, p16), made possible by electrospray ionization followed by ultrahigh-resolution Fourier transform ion cyclotron resonance mass analysis at 9.4 tesla. Further, a resolving power of m/Deltam50% approximately 8,000,000 has been achieved on bovine ubiquitin (8.6 kDa). These results represent a 10-fold increase in the highest mass at which isotopic fine structure previously had been observed. Finally, because isotopic fine structure reveals elemental composition directly, it can be used to confirm or determine molecular formula. For p16, for example, we were able to determine (5.1 +/- 0.3) the correct number (five) of sulfur atoms solely from the abundance ratio of the resolved 34S peak to the monoisotopic peak.

Application of micro-electrospray liquid chromatography techniques to FT-ICR MS to enable high-sensitivity biological analysis

A microbore electrospray (ESI) injection system has been adapted to our 9.4-tesla ESI FT-ICR mass spectrometer, greatly enhancing the stability and sensitivity of the system. Spray was generated from micro-ESI needles made from sharply tapered, polished fused silica capillaries of 25 to 50 microns inner diameter. Micro-ESI permits low-level sample analysis by constant infusion at sub-microL/min flow rate over a wide range of solvent conditions in both positive- and negative-ion mode. The system is flexible and allows rapid conversion to allow routine LC/MS analysis on low-level mixtures presented in biological media. LC/MS analyses were accomplished by replacing micro-ESI needles with capillaries packed with reverse phase retention media to permit analyte concentration and purification prior to analysis (micro-ESI/LC). A unique nano-flow LC pumping system was developed, capable of producing a true unsplit solvent gradient at flow rates below 1 microL/min. The micro-ESI/LC FT-ICR system produces mass spectra from a mixture of three neuroactive peptides at a concentration of 500 amol/microL (5 fmol each total loaded) in biological salts with baseline separation, signal-to-noise ratio of > 10:1 and mass resolving power > 5000. These results represent a reduction in detection limit by a factor of approximately 2 x 10(6) over the best previously published LC/FT-ICR MS data.

Restriction endonuclease from thermophilic bacterial species III. Isolation and characterization of BsiHKA I

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