The scavenger receptor cysteine-rich (SRCR) domain is an ancient and highly
conserved domain of about 110 residues which is found in diverse secreted and
cell-surface proteins, like the type I scavenger receptor, the speract
receptor, CD5/Ly-1, CD6, or complement factor I . Tandem repeats of SRCR
domains are common in the membrane bound proteins. Most SRCR domains have six
to eight cysteines that participate in intradomain disulfide bonds. SRCR
domains have been subdivided into two groups, A and B, primarily on the
differences in the spacing pattern between the cysteine residues [2,3].
Although the biochemical functions of SRCR domains have not been established
with certainty, they are likely to mediate protein-protein interactions and
ligand binding [2,3].
Determination of the crystal structure of the SRCR domain of M2BP reveals that
the M2NP SRCR adopts a compact fold of approximate dimensions 22 x 26 x 30
Angstrom, organized around a curved six-stranded β-sheet cradling an α-helix .
Some proteins known to contain one or more SRCR domains are listed below:
Mammalian macrophage scavenger receptor type I, a trimeric integral
membrane glycoprotein implicated in atherosclerosis, adhesion and host
defense. The scavenger receptor binds a variety of polyanions, including
chemically modified proteins and lipoproteins, and certain polynucleotides.
Mammalian CD5/Ly-1, a protein expressed at the cell surface of T
lymphocytes and a distinctive subset of B lymphocytes. It interacts with
CD72/Lyb-2. There are 3 copies of SRCR in CD5.
Mammalian CD6, a lymphocyte cell surface receptor that binds to its ligand,
activated leukocyte cell adhesion molecule (ALCAM/CD166), through the
membrane proximal of its three extracellular SRCR domains. There are 3
copies of SRCR in CD6.
Mammalian Mac-2 binding protein (M2BP), a tumor-associated antigen and
Mammalian and amphibian complement factor I (CFI), a protease that
regulates the complement cascade.
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