Crystal structure of the TRANCE/RANKL cytokine reveals determinants of receptor-ligand specificity
Jonathan Lam, … , Steven L. Teitelbaum, Daved H. Fremont
Jonathan Lam, … , Steven L. Teitelbaum, Daved H. Fremont
Published October 1, 2001
Citation Information: J Clin Invest. 2001;108(7):971-979. https://doi.org/10.1172/JCI13890.
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Article

Crystal structure of the TRANCE/RANKL cytokine reveals determinants of receptor-ligand specificity

Abstract

RANK, the receptor activator of NF-κB, and its ligand RANKL (initially termed TRANCE, also termed ODF and OPGL), are a TNF superfamily receptor-ligand pair that govern the development and function of osteoclasts, lymphoid tissue, and mammary epithelium. While TNF family cytokines share a common structural scaffold, individual receptor-ligand pairs associate with high specificity. Given the low level of amino acid conservation among members of the TNF superfamily, the means by which these molecules achieve specificity cannot be completely understood without knowledge of their three-dimensional structures. To determine the elements of RANKL that mediate RANK activation, we have crystallized the ectodomain of murine RANKL and solved its structure to a resolution of 2.6 Å. RANKL self-associates as a homotrimer with four unique surface loops that distinguish it from other TNF family cytokines. Mutagenesis of selected residues in these loops significantly modulates RANK activation, as evidenced by in vitro osteoclastogenesis, thereby establishing their necessity in mediating the biological activities of RANKL. Such structural determinants of RANKL-RANK specificity may be of relevance in the pharmacologic design of compounds to ameliorate osteopenic disorders of bone.

Authors

Jonathan Lam, Christopher A. Nelson, F. Patrick Ross, Steven L. Teitelbaum, Daved H. Fremont

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Structure-based alignment of TNF family cytokines with RANKL. The sequen...
Structure-based alignment of TNF family cytokines with RANKL. The sequence of the extracellular core domains of the TNF family cytokines TRAIL, CD40L, TNF-α, TNF-β, and ACRP30 are shown aligned to that of murine RANKL. Structural alignments to RANKL are based upon pairwise topological residue superposition of the crystal structure of RANKL with those of TRAIL (1d4v), CD40L (1aly), TNF-α (2tnf), TNF-β (1tnr), and ACRP30 (1c28). Residue numbers and secondary structure assignments for RANKL are depicted above the sequences. The ten β-strands that constitute the TNF family β-sandwich are drawn as green arrows, with standardized nomenclature. Solvent-accessible loops and coil regions connecting the β-strands are illustrated as brown lines. The AA′′ loop (orange line), connecting β-strands A and A′′, encompasses the A′ β-strand. Brown triangles above the residues indicate those involved in the trimeric interface of RANKL. The degree of homology at structurally equivalent positions among the family members (excluding ACRP30) is shown by colored circles below the sequences, 0–50% conservation (no circles), 50–90% (tan), >90% (brown). TRAIL residues boxed in green denote DR5 receptor contact sites on TRAIL. TNF-β residues boxed in magenta identify TNFR contact sites on TNF-β. By substituting RANKL in place of the ligands in the TRAIL:DR5 and TNF:TNFR co-crystal structures, we calculated potential contact sites for both of these receptors on RANKL. Boxed residues of RANKL indicate those calculated to physically contact DR5 (green), TNFR (magenta), or both (yellow) receptors during the docking analysis. Structural elements that are unique to RANKL are clustered in the solvent-accessible AA′′, CD, DE, and EF loops.