The terminal monosaccharide of cell surface glycoconjugates is typically a sialic acid (SA), and aberrant sialylation is involved in several diseases. Several methodological approaches in sample preparation and subsequent analysis using mass spectrometry (MS) have enabled the identification of glycosylation sites and the characterization of glycan structures. In this paper, we describe a protocol for the selective enrichment of SA-containing glycopeptides using a combination of titanium dioxide (TiO(2)) and hydrophilic interaction liquid chromatography (HILIC). The selectivity of TiO(2) toward SA-containing glycopeptides is achieved by using a low-pH buffer that contains a substituted acid such as glycolic acid to improve the binding efficiency and selectivity of SA-containing glycopeptides to the TiO(2) resin. By combining TiO(2) enrichment of sialylated glycopeptides with HILIC separation of deglycosylated peptides, a more comprehensive analysis of formerly sialylated glycopeptides by MS can be achieved. Here we illustrate the efficiency of the method by the identification of 1,632 unique formerly sialylated glycopeptides from 817 sialylated glycoproteins. The TiO(2)/HILIC protocol requires 2 d and the entire procedure from protein isolation can be performed in <5 d, depending on the time taken to analyze data.

Surfactant protein D (SP-D) plays important roles in the host defense against infectious microorganisms and in regulating the innate immune response to a variety of pathogen-associated molecular pattern. SP-D is mainly expressed by type II cells of the lung, but SP-D is generally found on epithelial surfaces and in serum. Genotyping for three single-nucleotide variations altering amino acids in the mature protein in codon 11 (Met11Thr), 160 (Ala160Thr), and 270 (Ser270Thr) of the SP-D gene was performed and related to the SP-D levels in serum. Individuals with the Thr/Thr11-encoding genotype had significantly lower SP-D serum levels than individuals with the Met/Met11 genotype. Gel filtration chromatography revealed two distinct m.w. peaks with SP-D immunoreactivity in serum from Met/Met11-encoding genotypes. In contrast, Thr/Thr11 genotypes lacked the highest m.w. form. A similar SP-D size distribution was found for recombinant Met11 and Thr11 expressed in human embryonic kidney cells. Atomic force microscopy of purified SP-D showed that components eluting in the position of the high m.w. peak consist of multimers, dodecamers, and monomers of subunits, whereas the second peak exclusively contains monomers. SP-D from both peaks bound to mannan-coated ELISA plates. SP-D from the high m.w. peak bound preferentially to intact influenza A virus and Gram-positive and Gram-negative bacteria, whereas the monomeric species preferentially bound to isolated LPS. Our data strongly suggest that polymorphic variation in the N-terminal domain of the SP-D molecule influences oligomerization, function, and the concentration of the molecule in serum.

Plasma membrane proteins that are exposed on the cell surface have important biological functions, such as signaling into and out of the cells, ion transport, and cell-cell and cell-matrix interactions. The expression level of many of the plasma membrane proteins involved in these key functions is altered on cancer cells, and these proteins may also be subject to post-translational modification, such as altered phosphorylation and glycosylation. Additional protein alterations on cancer cells confer metastatic capacities, and some of these cell surface proteins have already been successfully targeted by protein drugs, such as human antibodies, that have enhanced survival of several groups of cancer patients. The combination of novel analytical approaches and subcellular fractionation procedures has made it possible to study the plasma membrane proteome in more detail, which will elucidate cancer biology, particularly metastasis, and guide future development of novel drug targets. The technical advances in plasma membrane proteomics and the consequent biological revelations will be discussed herein. Many of the advances have been made using cancer cell lines, but because the main goal of this research is to improve individualized treatment and increase cancer patient survival, further development is crucial to direct analysis of clinically relevant patient samples. These efforts include optimized specimen handling and preparation as well as improved proteomics platforms.

The severe acute respiratory syndrome coronavirus (SARS-CoV) infects host cells with its surface glycosylated spike-protein (S-protein). Here we expressed the SARS-CoV S-protein to investigate its interactions with innate immune mechanisms in the lung. The purified S-protein was detected as a 210 kDa glycosylated protein. It was not secreted in the presence of tunicamycin and was detected as a 130 kDa protein in the cell lysate. The purified S-protein bound to Vero but not 293T cells and was itself recognized by lung surfactant protein D (SP-D), a collectin found in the lung alveoli. The binding required Ca(2+) and was inhibited by maltose. The serum collectin, mannan-binding lectin (MBL), exhibited no detectable binding to the purified S-protein. S-protein binds and activates macrophages but not dendritic cells (DCs). It suggests that SARS-CoV interacts with innate immune mechanisms in the lung through its S-protein and regulates pulmonary inflammation.

Highlights d Cholesterol biosynthesis is essential for breast cancer stem cell propagation d Expression of cholesterol synthesis proteins correlates with TNBC patient outcome d Inhibition of cholesterol biosynthesis reduces mammosphere formation