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Critical Reviews™ in Immunology

Impact factor: 3.857

ISSN Print: 1040-8401
ISSN Online: 2162-6472

Critical Reviews™ in Immunology

DOI: 10.1615/CritRevImmunol.v24.i1.10
38 pages

The Scavenger Receptor Cysteine-Rich (SRCR) Domain: An Ancient and Highly Conserved Protein Module of the Innate Immune System

Maria Rosa Sarrias
Sevei d’Immunologia, Institut Clinic d’Infeccions i Immunologia (ICII), Institut d’Investigacions Biomediques August Pi i Sunyer (IDIBAPS), Hospital Clinic, Barcelona, Spain
Jorn Gronlund
Immunology and Microbiology, Institute of Medical Biology, University of Southern Denmark, Odense, Denmark
Olga Padilla
Servei d’Immunologia, Institut Clinic d’Infeccions i Immunologia (ICII), Institut d’Investigacions Biomediques August Pi i Sunyer (IDIBAPS), Hospital Clinic, Barcelona, Spain
Jens Madsen
Immunology and Microbiology, Institute of Medical Biology, University of Southern Denmark, Odense, Denmark
Uffe Holmskov
Immunology and Microbiology, Institute of Medical Biology, University of Southern Denmark, Odense, Denmark
Francisco Lozano
Servei d’Immunologia, ICII, D'Investigacions Biomediques August Pi i Sunyer (IDIBAPS), Hospital Clinic; and Unitat d’Immunologia, Dept. de Biologia Cellular i Anatomia Patologica, Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain

ABSTRACT

The Scavenger Receptor Cysteine-Rich (SRCR) domain is an ancient and highly conserved protein module of ~100−110 amino acids, which defines a superfamily (SRCR-SF) of either soluble or membrane-bound receptors expressed by hematopoietic and nonhematopoietic cells, at either embryonic or adult stages. The existence of two types of SRCR domains allows the division of the SRCR-SF into two groups. Members of group A contain SRCR domains with 6 cysteine residues and are encoded by two exons, whereas those of group B usually contain 8 cysteines and are encoded by a single exon. Group A members usually present as multidomain mosaic proteins containing single SRCR domains associated to other functional domains, such as enzymatic (protease) domains or collagenous regions. On the contrary, group B members generally present as proteins exclusively composed of tandem repeats of SRCR domains, with or without the presence of CUB and ZP domains thought to be involved in oligomerization but never associated to protease domains. Representatives of either group are found in different animal species, from low invertebrates (sponges) to high vertebrates (mammals). Although no unifying function has been defined for SRCR-SF members, accumulated data, together with the high degree of structural and phylogenetic conservation of SRCR domains indicates that they might subserve basic homeostatic functions, including innate immune defense.