Modeled structural basis for the recognition of α2-3-sialyllactose by soluble Klotho.

Soluble Klotho (sKlotho) is the shed ectodomain of antiaging membrane Klotho that contains 2 extracellular domains KL1 and KL2, each of which shares sequence homology to glycosyl hydrolases. sKlotho elicits pleiotropic cellular responses with a poorly understood mechanism of action. Notably, in injury settings, sKlotho confers cardiac and renal protection by down-regulating calcium-permeable transient receptor potential canonical type isoform 6 (TRPC6) channels in cardiomyocytes and glomerular podocytes. Inhibition of PI3K-dependent exocytosis of TRPC6 is thought to be the underlying mechanism, and recent studies showed that sKlotho interacts with α2-3-sialyllactose-containing gangliosides enriched in lipid rafts to inhibit raft-dependent PI3K signaling. However, the structural basis for binding and recognition of α2-3-sialyllactose by sKlotho is unknown. Using homology modeling followed by docking, we identified key protein residues in the KL1 domain that are likely involved in binding sialyllactose. Functional experiments based on the ability of Klotho to down-regulate TRPC6 channel activity confirm the importance of these residues. Furthermore, KL1 domain binds α2-3-sialyllactose, down-regulates TRPC6 channels, and exerts protection against stress-induced cardiac hypertrophy in mice. Our results support the notion that sialogangliosides and lipid rafts are membrane receptors for sKlotho and that the KL1 domain is sufficient for the tested biologic activities. These findings can help guide the design of a simpler Klotho mimetic.-Wright, J. D., An, S.-W., Xie, J., Yoon, J., Nischan, N., Kohler, J. J., Oliver, N., Lim, C., Huang, C.-L. Modeled structural basis for the recognition of α2-3-sialyllactose by soluble Klotho. © FASEB.