Although involvement of informational sugar chains has proved essential in extensive biological phenomena, explanations given for understanding the true meaning of sugar recognition are not satisfactory except in a limited number of cases. Comprehension of the peculiar nature of sugar recognition is essential for understanding the true roles of sugar chains in life. This article is intended to give some clue for better understanding of sugar recognition, completely different from recognition of nucleic acids and proteins, on the basis of three key words, non-linear, fuzzy, and weak.
Many therapeutic antibodies have been approved since the late 1990s, and these agents represent a major new class of drugs. However, there still remains room for improvement in the clinical effect and cost of therapeutic antibodies licensed on the market. Most therapeutic antibodies, which currently have been developed as medical agents, are human IgG1 whose molecular weight is approximately 150kDa. Human IgG1 is a glycoprotein bearing two N-linked oligosaccharides bound to the antibody constant region (Fc), and exercises its effector functions of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) through the interaction of the Fc with either lymphocyte receptors (FcγRs) or complements. Recently, therapeutic antibodies have been shown to improve overall survival as well as time to disease progression in a variety of human malignancies such as breast, colon and haematological cancers (1-4), and genetic analysis of FcγR polymorphisms of cancer patients has demonstrated that ADCC is a major anti-neoplasm mechanism responsible for the clinical efficacy of anti-CD20 antibody RituxanR (rituximab) and anti-Her2 antibody HerceptinR (trastuzumab) (5-9). Thus, there are currently numerous efforts to improve ADCC of therapeutic antibodies. We have found that the removal of fucose residues from the biantennary complex-type oligosaccharides attached to the Fc dramatically enhances the ADCC of the IgG due to improved FcγARIIIa binding (10-17), and have developed the technology, designated as PotelligentTM, to control the fucosylation of therapeutic antibodies (18, 19). Application of this technology has now started for the development of the next generation of more effective therapeutic antibodies.
A multi-specific enzyme, neopullulanase (EC 184.108.40.206) catalyzes the hydrolysis of α-1, 4- and α-1, 6-glucosidic linkages, as well as transglycosylation to form α-1, 4- and α-1, 6-glucosidic linkages. Based on the series of experimental results using neopullulanase, we pointed out the structural similarity and the common catalytic mechanism of the enzymes that catalyze these four reactions, and thus, proposed and defined the concept of α-amylase family. Mutational analyses provided the evidence that the only one active center of neopullulanase participate in all four reactions; the hydrolysis of α-1, 4- and α-1, 6-glucosidic linkages and transglycosylation to form α-1, 4- and α-1, 6-glucosidic linkages. Structural analyses provided the conclusive proof that only the one active center of neopullulanase participates in all four reactions. We have been trying to interconvert glucanohydrolases/ glucanotransferases, and change their specificity and create tailor-made industrially useful enzymes based on the concept of the α-amylase family. The concept of the α-amylase family is demonstrated here again as a rational tool for protein engineering of glycoenzymes.
The human genome project has provided biology and medicine with tremendous resources. The field of glycobiology is no exception. During recent years, we glycobiologists have actively incorporated gene-engineering techniques into our methodology. An amazing fact of gene engineering technology is that DNA and recombinant proteins can be amplified unlimitedly, an approach opposite to that of old-fashioned biochemistry, in which we started an experiment with large amounts of material and ended up with a very small amount of purified sample. Nonetheless, although we can now produce recombinant glycosyltransferases, we cannot produce the carbohydrate itself. In this regard, peptide-displaying phage is worth being recognized as the method breaking this dilemma, by being equivalent to produce recombinant carbohydrates as this technology can amplify specific oligosaccharide mimicries. This mini review describes pioneering works introducing peptide-displaying phage to glycobiology and potential applications of carbohydrate-mimicking peptides to cancer research.