Glycoprofiling of the Human Salivary Proteome

Abstract

Glycosylation is important for a number of biological processes and is perhaps the most abundant and complicated of the known post-translational modifications found on proteins. This work combines two-dimensional polyacrylamide gel electrophoresis (2-DE) and lectin blotting to map the salivary glycome, and mass spectrometry to identity the proteins that are associated with the glycome map. A panel of 15 lectins that recognize six sugar-specific categories was used to visualize the type and extent of glycosylation in saliva from two healthy male individuals. Lectin blots were compared to 2-D gels stained either with Sypro Ruby (protein stain) or Pro-Q Emerald 488 (glycoprotein stain). Each lectin shows a distinct pattern, even those belonging to the same sugar-specific category. In addition, the glycosylation profiles generated from the lectin blots show that most of the salivary proteins are glycosylated and that the pattern is more widespread than is demonstrated by the glycoprotein stained gel. Finally, the co-reactivity between two lectins was measured to determine the glycan structures that are most and least often associated with one another along with the population variation of the lectin reactivity for 66 individuals.

Figure 1

Total protein and glycoprotein stained 2-D gels. Whole saliva was subjected to isoelectric focusing on a pH 3-10 nonlinear IPG strip, which was then resolved in the second dimension on a 12.5% SDS-PAGE gel. The resulting gels were either stained with SYPRO Ruby total protein stain (A) or Pro-Q Emerald 488 glycoprotein stain (B). Labeled are the protein spots that were identified from the Sypro Ruby stained gel either by MALDI-TOF MS in our previous work [7] or by LC-MS/MS in this work.

Figure 1

Total protein and glycoprotein stained 2-D gels. Whole saliva was subjected to isoelectric focusing on a pH 3-10 nonlinear IPG strip, which was then resolved in the second dimension on a 12.5% SDS-PAGE gel. The resulting gels were either stained with SYPRO Ruby total protein stain (A) or Pro-Q Emerald 488 glycoprotein stain (B). Labeled are the protein spots that were identified from the Sypro Ruby stained gel either by MALDI-TOF MS in our previous work [7] or by LC-MS/MS in this work.

Figure 2

2-D lectin blots. Two-dimensional gels containing whole saliva were transferred and probed with either lectin DSL (A), LEL (B), UEA I (C), AAL (D), or WGA (E). The spots were matched to the Sypro Ruby stained gel shown in Figure 1A and scored for having high, medium, low, or no reactivity (Supplemental Table).

Figure 2

2-D lectin blots. Two-dimensional gels containing whole saliva were transferred and probed with either lectin DSL (A), LEL (B), UEA I (C), AAL (D), or WGA (E). The spots were matched to the Sypro Ruby stained gel shown in Figure 1A and scored for having high, medium, low, or no reactivity (Supplemental Table).

Figure 2

2-D lectin blots. Two-dimensional gels containing whole saliva were transferred and probed with either lectin DSL (A), LEL (B), UEA I (C), AAL (D), or WGA (E). The spots were matched to the Sypro Ruby stained gel shown in Figure 1A and scored for having high, medium, low, or no reactivity (Supplemental Table).

Figure 2

2-D lectin blots. Two-dimensional gels containing whole saliva were transferred and probed with either lectin DSL (A), LEL (B), UEA I (C), AAL (D), or WGA (E). The spots were matched to the Sypro Ruby stained gel shown in Figure 1A and scored for having high, medium, low, or no reactivity (Supplemental Table).

Figure 2

2-D lectin blots. Two-dimensional gels containing whole saliva were transferred and probed with either lectin DSL (A), LEL (B), UEA I (C), AAL (D), or WGA (E). The spots were matched to the Sypro Ruby stained gel shown in Figure 1A and scored for having high, medium, low, or no reactivity (Supplemental Table).