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Glycoproteins of the scavenger receptor cysteine-rich (SRCR) superfamily contain one or more protein modules homologous to the membrane-distal domain of macrophage scavenger receptor I. These domains can be found in the extracellular regions of membrane proteins and in secreted glycoproteins, from the most primitive species to vertebrates. A systematic, bioinformatics-based search for putative human proteins related to the forty-seven known human group B SRCR domains identified a new family member that we have called Soluble Scavenger with 5 Domains (SSc5D). SSc5D is a new soluble protein whose expression is restricted to monocytes/macrophages and T-lymphocytes, and is particularly enriched in the placenta. The gene encoding SSc5D spans 30kb of genomic DNA, and contains fourteen exons producing a 4.8kb-long mRNA. The mature polypeptide is predicted to consist of 1573 amino acids comprising, towards the N-terminus, five very similar SRCR domains that are highly conserved among non-marsupial mammals, and a large (>250nm), very heavily glycosylated, mucin-like sequence towards the C-terminus. Each of the SRCR domains is encoded by a single exon, and contains eight cysteine residues, as observed for all other group B SRCR domains. A shorter isoform encoded by a weakly expressed, alternatively spliced transcript, which lacks the mucin-like C-terminal region, was also identified. It seems likely that SSc5D has a role at the interface between adaptive and innate immunity, or in placental function.

Original publication




Journal article


Mol Immunol

Publication Date





2585 - 2596


Amino Acid Sequence, Blotting, Northern, Cell Line, Cell Line, Tumor, Cloning, Molecular, Female, Gene Expression Profiling, Humans, Macrophages, Molecular Sequence Data, Monocytes, Phylogeny, Placenta, Protein Isoforms, RNA, Messenger, Reverse Transcriptase Polymerase Chain Reaction, Scavenger Receptors, Class B, Sequence Homology, Amino Acid, T-Lymphocytes