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.

Department of Biochemistry Faculty of Science Charles University Prague Hlavova 8 CZ 12840 Praha 2 Czech Republic

Biochemistry. 2013 Dec 23;52(51):9403. doi: 10.1021/bi401605t. PubMed

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Nkrp1 family, from lectins to protein interacting molecules

Re-evaluation of binding properties of recombinant lymphocyte receptors NKR-P1A and CD69 to chemically synthesized glycans and peptides