Structural Aspects of Carbohydrate Recognition Mechanisms of C-Type Lectins

Carbohydrate recognition is an essential function occurring in all living organisms. Lectins are carbohydrate-binding proteins and are classified into several families. In mammals, Ca2+-dependent C-type lectins, such as β-galactoside-binding galectin and

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Introduction.......................................................................................................................... C-Type Lectin Fold ............................................................................................................. Sugar Binding Motifs: EPN and QPD................................................................................ 3.1 Other Monosaccharide Binding Modes ..................................................................... 4 Oligosaccharide Recognition............................................................................................... 4.1 Oligosaccharide Recognition via EPN Motif ............................................................ 4.2 Oligosaccharide Recognition of QPD Motif-Containing C-Type Lectins ................ 4.3 Oligosaccharide Recognition of C-Type Lectin-like Domains ................................. 4.4 Genetic Variants of C-Type Lectins .......................................................................... 5 Functional Oligomerization of C-Type Lectin Domains.................................................... 6 Conclusion and Future Perspective..................................................................................... References ..................................................................................................................................

Abstract Carbohydrate recognition is an essential function occurring in all living organisms. Lectins are carbohydrate-binding proteins and are classified into several families. In mammals, Ca2+-dependent C-type lectins, such as b-galactosidebinding galectin and sialic acid-binding siglec, play crucial roles in the immune response and homeostasis. C-type lectins are abundant and diverse in animals. Their immunological activities include lymphocyte homing, pathogen recognition, and clearance of apoptotic bodies. C-type lectin domains are composed of 110–130 amino acid residues with highly conserved structural folds. Remarkably, individual lectins can accept a wide variety of sugar ligands and can distinguish subtle M. Nagae (&) Department of Pharmaceutical Sciences, The University of Tokyo, Hongo 7-3-1, Bunkyo-Ku, Tokyo 113-0033, Japan e-mail: [email protected] Y. Yamaguchi (&) Faculty of Pharmaceutical Sciences, Tohoku Medical and Pharmaceutical University, Miyagi 981-8558, Japan e-mail: [email protected] Current Topics in Microbiology and Immunology https://doi.org/10.1007/82_2019_181 © Springer Nature Switzerland AG 2019

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M. Nagae and Y. Yamaguchi

structural differences in closely related ligands. In addition, several C-type lectin-like proteins specifically bind to carbohydrate ligands in Ca2+-independent ways. The accumulated 3D structural evidence clarifies the unexpected structural versatility of C-type lectins underlying the variety of ligand binding modes. In this issue, we focus on the structural aspects of carbohydrate recognition mechanisms of C-type lectins and C-type lectin-like proteins.

1 Introduction Car