The sweet and sour of serological glycoprotein tumor biomarker quantification

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Abstract

Aberrant and dysregulated protein glycosylation is a well-established event in the process of oncogenesis and cancer progression. Years of study on the glycobiology of cancer have been focused on the development of clinically viable diagnostic applications of this knowledge. However, for a number of reasons, there has been only sparse and varied success. The causes of this range from technical to biological issues that arise when studying protein glycosylation and attempting to apply it to practical applications. This review focuses on the pitfalls, advances, and future directions to be taken in the development of clinically applicable quantitative assays using glycan moieties from serum-based proteins as analytes. Topics covered include the development and progress of applications of lectins, mass spectrometry, and other technologies towards this purpose. Slowly but surely, novel applications of established and development of new technologies will eventually provide us with the tools to reach the ultimate goal of quantification of the full scope of heterogeneity associated with the glycosylation of biomarker candidate glycoproteins in a clinically applicable fashion.

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Most cited references 148

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Intracellular functions of N-linked glycans.

A. Helenius, M. Aebi (2001)

N-linked oligosaccharides arise when blocks of 14 sugars are added cotranslationally to newly synthesized polypeptides in the endoplasmic reticulum (ER). These glycans are then subjected to extensive modification as the glycoproteins mature and move through the ER via the Golgi complex to their final destinations inside and outside the cell. In the ER and in the early secretory pathway, where the repertoire of oligosaccharide structures is still rather small, the glycans play a pivotal role in protein folding, oligomerization, quality control, sorting, and transport. They are used as universal "tags" that allow specific lectins and modifying enzymes to establish order among the diversity of maturing glycoproteins. In the Golgi complex, the glycans acquire more complex structures and a new set of functions. The division of synthesis and processing between the ER and the Golgi complex represents an evolutionary adaptation that allows efficient exploitation of the potential of oligosaccharides.

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On the frequency of protein glycosylation, as deduced from analysis of the SWISS-PROT database.

R. Apweiler, H Hermjakob, N. Sharon (1999)

The SWISS-PROT protein sequence data bank contains at present nearly 75,000 entries, almost two thirds of which include the potential N-glycosylation consensus sequence, or sequon, NXS/T (where X can be any amino acid but proline) and thus may be glycoproteins. The number of proteins filed as glycoproteins is however considerably smaller, 7942, of which 749 have been characterized with respect to the total number of their carbohydrate units and sites of attachment of the latter to the protein, as well as the nature of the carbohydrate-peptide linking group. Of these well characterized glycoproteins, about 90% carry either N-linked carbohydrate units alone or both N- and O-linked ones, attached at 1297 N-glycosylation sites (1.9 per glycoprotein molecule) and the rest are O-glycosylated only. Since the total number of sequons in the well characterized glycoproteins is 1968, their rate of occupancy is 2/3. Assuming that the same number of N-linked units and rate of sequon occupancy occur in all sequon containing proteins and that the proportion of solely O-glycosylated proteins (ca. 10%) will also be the same as among the well characterized ones, we conclude that the majority of sequon containing proteins will be found to be glycosylated and that more than half of all proteins are glycoproteins.

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Protein glycosylation: nature, distribution, enzymatic formation, and disease implications of glycopeptide bonds.

R G Spiro (2002)

Formation of the sugar-amino acid linkage is a crucial event in the biosynthesis of the carbohydrate units of glycoproteins. It sets into motion a complex series of posttranslational enzymatic steps that lead to the formation of a host of protein-bound oligosaccharides with diverse biological functions. These reactions occur throughout the entire phylogenetic spectrum, ranging from archaea and eubacteria to eukaryotes. It is the aim of this review to describe the glycopeptide linkages that have been found to date and specify their presence on well-characterized glycoproteins. A survey is also made of the enzymes involved in the formation of the various glycopeptide bonds as well as the site of their intracellular action and their affinity for particular peptide domains is evaluated. This examination indicates that 13 different monosaccharides and 8 amino acids are involved in glycoprotein linkages leading to a total of at least 41 bonds, if the anomeric configurations, the phosphoglycosyl linkages, as well as the GPI (glycophosphatidylinositol) phosphoethanolamine bridge are also considered. These bonds represent the products of N- and O-glycosylation, C-mannosylation, phosphoglycation, and glypiation. Currently at least 16 enzymes involved in their formation have been identified and in many cases cloned. Their intracellular site of action varies and includes the endoplasmic reticulum, Golgi apparatus, cytosol, and nucleus. With the exception of the Asn-linked carbohydrate and the GPI anchor, which are transferred to the polypeptide en bloc, the sugar-amino acid linkages are formed by the enzymatic transfer of an activated monosaccharide directly to the protein. This review also deals briefly with glycosidases, which are involved in physiologically important cleavages of glycopeptide bonds in higher organisms, and with a number of human disease states in which defects in enzymatic transfer of saccharides to protein have been implicated.

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Author and article information

Contributors

Uros Kuzmanov

Hari Kosanam

Eleftherios P Diamandis

Journal

Journal ID (nlm-ta): BMC Med

Journal ID (iso-abbrev): BMC Med

Title: BMC Medicine

Publisher: BioMed Central

ISSN (Electronic): 1741-7015

Publication date Collection: 2013

Publication date (Electronic): 7 February 2013

Volume: 11

Page: 31

Affiliations

[1 ]Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, 6th floor, 60 Murray Street, Box 32, Toronto, ON M5T 3L9, Canada

[2 ]Department of Pathology and Laboratory Medicine, Mount Sinai Hospital, 6th Floor, 60 Murray Street, Box 32, Toronto, ON M5T 3L9, Canada

[3 ]Department of Clinical Biochemistry, University Health Network, 6th Floor, 60 Murray Street, Box 32, Toronto, ON M5T 3L9, Canada

Article

Publisher ID: 1741-7015-11-31

DOI: 10.1186/1741-7015-11-31

PMC ID: 3751898

PubMed ID: 23390961

SO-VID: dc71919a-96d9-413c-b004-8a3133cc0aab

License:

This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

The sweet and sour of serological glycoprotein tumor biomarker quantification

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Cardiovascular Innovations and Applications

Most cited references 148

Intracellular functions of N-linked glycans.

On the frequency of protein glycosylation, as deduced from analysis of the SWISS-PROT database.

Protein glycosylation: nature, distribution, enzymatic formation, and disease implications of glycopeptide bonds.

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