Title: Crystal structure of the m4-1BB/4-1BBL complex reveals an unusual dimeric ligand that undergoes structural changes upon 4-1BB receptor binding

Abstract

The interaction between the receptor 4-1BB and its ligand 4-1BBL provides co-stimulatory signals for T-cell activation and proliferation. However, differences in the mouse and human molecules might result in differential engagement of this pathway. Here, we report the crystal structure of mouse 4-1BBL and of the mouse 4-1BB/4-1BBL complex, which together provided insights into the molecular mechanism by which m4-1BBL and its cognate receptor recognize each other. Unlike all human or mouse tumor necrosis factor ligands that form noncovalent and mostly trimeric assemblies, the m4-1BBL structure formed a disulfide-linked dimeric assembly. The structure disclosed that certain differences in the amino acid composition along the intramolecular interface, together with two specific residues (Cys-246 and Ser-256) present exclusively in m4-1BBL, are responsible for this unique dimerization. Unexpectedly, upon m4-1BB binding, m4-1BBL undergoes structural changes within each protomer; moreover, the individual m4-1BBL protomers rotate relative to each other, yielding a dimerization interface with more inter-subunit interactions. We also observed that in the m4-1BB/4-1BBL complex, each receptor monomer binds exclusively to a single ligand subunit with contributions of cysteine-rich domain 1 (CRD1), CRD2, and CRD3. Furthermore, structure-guided mutagenesis of the binding interface revealed that novel binding interactions with the GH loop, rather than themore » DE loop, are energetically critical and define the m4-1BB receptor selectivity for m4-1BBL. As a result, a comparison with the human 4-1BB/4-1BBL complex highlighted several differences between the ligand- and receptor-binding interfaces, providing an explanation for the absence of inter-species cross-reactivity between human and mouse 4-1BB and 4-1BBL molecules.« less

Authors:

Bitra, Aruna  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-1675-3544"
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Doukov, Tzanko  ^[2];

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• Search DOE PAGES for ORCID "0000-0001-8625-2572"
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Destito, Giuseppe ^[3]; Croft, Michael ^[4]; Zajonc, Dirk M.  ^[5]

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• Search DOE PAGES for ORCID "0000-0001-7215-1981"
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+ Show Author Affiliations

1. La Jolla Inst. for Immunology (LJI), La Jolla, CA (United States)
2. SLAC National Accelerator Lab., Menlo Park, CA (United States)
3. Kirin Kyowa Hakko Pharmaceutical Research, La Jolla, CA (United States)
4. La Jolla Inst. for Immunology (LJI), La Jolla, CA (United States); Univ. of California San Diego, La Jolla, CA (United States)
5. La Jolla Inst. for Immunology (LJI), La Jolla, CA (United States); Ghent Univ., Ghent (Belgium)

Publication Date:

2018-12-13

Research Org.:

SLAC National Accelerator Lab., Menlo Park, CA (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1506962

Grant/Contract Number:  

AC02-76SF00515; AI110929; P41GM103393

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Biological Chemistry

Additional Journal Information:

Journal Volume: 294; Journal Issue: 6; Journal ID: ISSN 0021-9258

Publisher:

American Society for Biochemistry and Molecular Biology

Country of Publication:

United States

Language:

English

Subject:

60 APPLIED LIFE SCIENCES; tumor necrosis factor (TNF); protein–protein interaction; protein structure; cell surface receptor; X-ray crystallography; 4-1BB; 4-1BB ligand; CD137; CD137L; TNFRSF9; immune cell