Crystal Structure of the Extracellular Domain of the Human Dendritic Cell Surface Marker CD83.
CD83 is a type-I membrane protein and an efficient marker for identifying mature dendritic cells. Whereas membrane-bound, full-length CD83 co-stimulates the immune system, a soluble variant (sCD83), consisting of the extracellular domain only, displays strong immune-suppressive activities. Besides a prediction that sCD83 adopts a V-set Ig-like fold, however, little is known about the molecular architecture of CD83 and the mechanism by which CD83 exerts its function on dendritic cells and additional immune cells. Here, we report the crystal structure of human sCD83 up to a resolution of 1.7Å solved in three different crystal forms. Interestingly, β-strands C', C″, and D that are typical for V-set Ig-domains could not be traced in sCD83. Mass spectrometry analyses, limited proteolysis experiments, and bioinformatics studies show that the corresponding segment displays enhanced main-chain accessibility, extraordinary low sequence conservation, and a predicted high disorder propensity. Chimeric proteins with amino acid swaps in this segment show unaltered immune-suppressive activities in a TNF-α assay when compared to wild-type sCD83. This strongly indicates that this segment does not participate in the biological activity of CD83. The crystal structure of CD83 shows the recurrent formation of dimers and trimers in the various crystal forms and reveals strong structural similarities between sCD83 and B7 family members and CD48, a signaling lymphocyte activation molecule family member. This suggests that CD83 exerts its immunological activity by mixed homotypic and heterotypic interactions as typically observed for proteins present in the immunological synapse.
Department of Immune Modulation, University Hospital Erlangen, Friedrich-Alexander-University Erlangen-Nürnberg, Hartmannstr. 14, D-91052 Erlangen, Germany.
Christiane S
CS
Heilingloh
Division of Biotechnology, Department of Biology, Friedrich-Alexander-University Erlangen-Nürnberg, Henkestr. 91, D-91052 Erlangen, Germany.
Stefan
S
Klingl
Division of Biotechnology, Department of Biology, Friedrich-Alexander-University Erlangen-Nürnberg, Henkestr. 91, D-91052 Erlangen, Germany.
Claudia
C
Egerer-Sieber
Division of Biotechnology, Department of Biology, Friedrich-Alexander-University Erlangen-Nürnberg, Henkestr. 91, D-91052 Erlangen, Germany.
Benedikt
B
Schmid
Division of Biotechnology, Department of Biology, Friedrich-Alexander-University Erlangen-Nürnberg, Henkestr. 91, D-91052 Erlangen, Germany.
Sigrid
S
Weiler
Department of Immune Modulation, University Hospital Erlangen, Friedrich-Alexander-University Erlangen-Nürnberg, Hartmannstr. 14, D-91052 Erlangen, Germany.
Petra
P
Mühl-Zürbes
Division of Biochemistry, Department of Biology, Friedrich-Alexander-University Erlangen-Nürnberg, Staudtstr. 5, D-91058 Erlangen, Germany.
Jörg
J
Hofmann
Division of Bioinformatics, Institute of Biochemistry, Friedrich-Alexander-University Erlangen-Nürnberg, Fahrstraße 17, D-91054 Erlangen, Germany.
Joachim D
JD
Stump
Division of Bioinformatics, Institute of Biochemistry, Friedrich-Alexander-University Erlangen-Nürnberg, Fahrstraße 17, D-91054 Erlangen, Germany.
Heinrich
H
Sticht
Department of Immune Modulation, University Hospital Erlangen, Friedrich-Alexander-University Erlangen-Nürnberg, Hartmannstr. 14, D-91052 Erlangen, Germany.
Mirko
M
Kummer
Department of Immune Modulation, University Hospital Erlangen, Friedrich-Alexander-University Erlangen-Nürnberg, Hartmannstr. 14, D-91052 Erlangen, Germany.
Alexander
A
Steinkasserer
Division of Biotechnology, Department of Biology, Friedrich-Alexander-University Erlangen-Nürnberg, Henkestr. 91, D-91052 Erlangen, Germany. Electronic address: yves.muller@fau.de.
Yves A
YA
Muller
D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000737:chemistry* / Q000378:metabolism; D015415:Biomarkers / Q000737:chemistry; D017124:Conserved Sequence; D018360:Crystallography, X-Ray; D003713:Dendritic Cells / Q000276:immunology*; D006801:Humans; D007136:Immunoglobulins / Q000737:chemistry* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D011487:Protein Conformation; D000072417:Protein Domains; D055503:Protein Multimerization; D000097802:CD83 Antigen
D015703:Antigens, CD; D015415:Biomarkers; D007136:Immunoglobulins; D008562:Membrane Glycoproteins; D000097802:CD83 Antigen
V-set Ig-domain; X-ray crystallography; homotypic interactions; immune co-stimulation and -suppression; structure–function relationships