Alterations in the carbohydrate structures of an abnormal protein from sera of patients with rheumatoid arthritis

Quantitative glycomics of human whole serum glycoproteins based on the standardized protocol for liberating N-glycans

Global glycomics of human whole serum glycoproteins appears to be an innovative and comprehensive approach to identify surrogate non-invasive biomarkers for various diseases. Despite the fact that quantitative glycomics is premised on highly efficient and reproducible oligosaccharide liberation from human serum glycoproteins, it should be noted that there is no validated protocol for which deglycosylation efficiency is proven to be quantitative. To establish a standard procedure to evaluate N-glycan release from whole human serum glycoproteins by peptide-N-glycosidase F (PNGase F) treatment, we determined the efficiencies of major N-glycan liberation from serum glycoproteins in the presence of reducing agents, surfactants, protease treatment, or combinations of pretreatments prior to PNGase F digestion. We show that de-N-glycosylation efficiency differed significantly depending on the condition used, indicative of the importance of a standardized protocol for the accumulation and comparison of glycomics data. Maximal de-N-glycosylation was achieved when serum was subjected to reductive alkylation in the presence of 2-hydroxyl-3-sulfopropyl dodecanoate, a surfactant used for solubilizing proteins, or related analogues, followed by tryptic digestion prior to PNGase F treatment. An optimized de-N-glycosylation protocol permitted relative and absolute quantitation of up to 34 major N-glycans present in serum glycoproteins of normal subjects for the first time. Moreover PNGase F-catalyzed de-N-glycosylation of whole serum glycoproteins was characterized kinetically, allowing accurate simulation of PNGase F-catalyzed de-N-glycosylation required for clinical glycomics using human serum samples. The results of the current study may provide a firm basis to identify new diagnostic markers based on serum glycomics analysis.

Increased levels of galactose-deficient IgG in sera of HIV-1-infected individuals

BACKGROUND

The IgG from sera of patients with chronic inflammatory diseases of autoimmune character or some chronic microbial infections is frequently deficient in galactose on N-linked glycans. However, this phenomenon has not been investigated at length in human viral infections.

OBJECTIVES

To evaluate the glycosylation of serum IgG in HIV-1-positive patients.

METHODS

Psathyrella velutina lectin was used in enzyme-linked immunosorbent and Western blot assays to determine glycosylation. In addition, gas-liquid chromatography and mass spectrometry were utilized to confirm the galactose deficiency observed in the lectin-binding assays.

RESULTS

HIV-1-infected individuals had significantly higher levels of galactose-deficient IgG than healthy controls. In fact, the galactose deficiency of the N-linked glycans observed in other diseases was even more profound in HIV-1 infection. This deficiency was primarily restricted to IgG when total serum glycoproteins were evaluated and IgG1 was the subclass most affected in all patients. Also, a significant increase in lectin binding was observed on IgG2 and IgG4 from HIV-1-positive females compared with HIV-1-negative females.

CONCLUSIONS

Identification of deficient galactosylation of serum IgG from HIV-1-infected patients extended the spectrum of diseases in which this phenomenon has been observed. In addition, the results suggest yet another aspect of immune dysfunction as a result of HIV-1 infection.

Presence of an acidic glycoprotein in the serum of arthritic rats: modulation by capsaicin and curcumin

Levels of various serum proteins were found to change in adjuvant induced arthritis. Increased levels of a glycoprotein with an apparent molecular weight of 72 kDa (Gp A72) were observed in the sera of arthritic rats. Gp A72 is an acidic glycoprotein with a pI of 5.1. Gp A72 also showed antitryptic activity. The appearance of Gp A72 in the serum preceded the onset of paw inflammation in arthritic rats and persisted in the chronic phase. Oral administration of the antiinflammatory spice principles-capsaicin (from red pepper) and curcumin (from turmeric) lowered the levels of Gp A72 by 88 and 73% respectively with concomitant lowering of paw inflammation in arthritic rats.