title: Molecular characterization of binding of calcium and carbohydrates by an early activation antigen of lymphocytes CD69.
abstract: CD69 is the earliest leukocyte activation antigen playing a pivotal role in cellular signaling. Here, we show that a globular C-terminal domain of CD69 belonging to C-type lectins binds calcium through Asp 171, Glu 185, and Glu 187 with K(d) approximately 54 microM. Closure of the calcium-binding site results in a conformational shift of Thr 107 and Lys 172. Interestingly, structural changes in all of these amino acids lead to the formation of high-affinity binding sites for N-acetyl-D-glucosamine. Similarly, a structural change in Glu 185 and Glu 187 contributes to a high-affinity site for N-acetyl-D-galactosamine. Site-directed mutagenesis and molecular modeling allowed us to describe the structural details of binding sites for both carbohydrates. These studies explain the importance of calcium for recognition of carbohydrates by CD69 and provide an important paradigm for the role of weak interactions in the immune system.
authors.affiliation: Department of Biochemistry, Faculty of Science, Charles University in Prague, Hlavova 8, CZ-12840 Praha 2, Czech Republic.
authors.forename: Jirí
authors.initials: J
authors.lastname: Pavlícek
authors.forename: Bruno
authors.initials: B
authors.lastname: Sopko
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Ettrich
authors.forename: Vladimír
authors.initials: V
authors.lastname: Kopecký
authors.forename: Vladimír
authors.initials: V
authors.lastname: Baumruk
authors.forename: Petr
authors.initials: P
authors.lastname: Man
authors.forename: Vladimír
authors.initials: V
authors.lastname: Havlícek
authors.forename: Marek
authors.initials: M
authors.lastname: Vrbacký
authors.forename: Ludmila
authors.initials: L
authors.lastname: Martínková
authors.forename: Vladimír
authors.initials: V
authors.lastname: Kren
authors.forename: Miloslav
authors.initials: M
authors.lastname: Pospísil
authors.forename: Karel
authors.initials: K
authors.lastname: Bezouska
mesh_terms: D000117:Acetylglucosamine / Q000378:metabolism*; D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D000945:Antigens, Differentiation, T-Lymphocyte / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D017931:DNA Primers / Q000737:chemistry; D004926:Escherichia coli; D006801:Humans; D007700:Kinetics; D037181:Lectins, C-Type; D008214:Lymphocytes / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D016133:Polymerase Chain Reaction; D017510:Protein Folding; D017386:Sequence Homology, Amino Acid; D000099192:CD69 Antigens
chemical_list: D000117:Acetylglucosamine; D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D002118:Calcium; D017931:DNA Primers; D037181:Lectins, C-Type; D000099192:CD69 Antigens