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Abstract
SREC‐II (scavenger receptor expressed by endothelial cells II) is a membrane protein encoded by the SCARF2 gene, with high homology to class F scavenger receptor SR‐F1, but no known scavenging function. We produced the extracellular domain of SREC‐II in a recombinant form and investigated its capacity to interact with common scavenger receptor ligands, including acetylated low‐density lipoprotein (AcLDL) and maleylated or acetylated BSA (MalBSA or AcBSA). Whereas no binding was observed for AcLDL, SREC‐II ectodomain interacted strongly with MalBSA and bound with high affinity to AcBSA, a property shared with the SR‐F1 ectodomain. SREC‐II ectodomain also interacted with two SR‐F1‐specific ligands, complement C1q and calreticulin, with affinities in the 100 nm range. We proceeded to generate a stable CHO cell line overexpressing full‐length SREC‐II; binding of MalBSA to these cells was significantly increased compared with nontransfected CHO cells. In contrast, no increase in binding could be detected for C1q and calreticulin. We show for the first time that SREC‐II has the capacity to interact with the common scavenger receptor ligand MalBSA. In addition, our data highlight similarities and differences in the ligand binding properties of SREC‐II in soluble form and at the cell surface, and show that endogenous protein ligands of the ectodomain of SREC‐II, such as C1q and calreticulin, are shared with the corresponding domain of SR‐F1.
Highlights
The scavenger receptor expressed by endothelial cells SREC-II, a membrane protein encoded by the SCARF2 gene, was discovered by identification of paralogous sequences with SCARF1, the gene coding for scavenger receptor expressed by endothelial cells SREC-I [1]
Given the high sequence homology of SREC-II and SR-F1 extracellular domains and in the light of our recent study showing the capacity of SR-F1 to bind complement C1q and CRT [6], we explored the capacity of SREC-II to interact with these proteins and revisited its capacity to interact with classical scavenger receptor ligands
We showed that C1q binds to the ectodomain of SREC-II with high affinity, a property shared with SR-F1 [6], and with Megf10/SR-F2 [15]
Summary
The scavenger receptor expressed by endothelial cells SREC-II, a membrane protein encoded by the SCARF2 gene, was discovered by identification of paralogous sequences with SCARF1, the gene coding for scavenger receptor expressed by endothelial cells SREC-I [1]. SREC-II is a transmembrane protein that contains ten EGF-like repeats in the extracellular domain and shares 52 % sequence identity with SR-F1 over the ectodomain of mature protein (402 amino acids) This suggests that the ectodomains of both receptors presumably share some biological properties. Apoptotic cells sensing was reported to be specific of SR-F1 [7], we were interested in exploring SREC-II possible interactions with C1q and CRT, and with an emblematic scavenger receptor ligand, maleylated BSA (MalBSA). For this purpose, we produced the extracellular domain of SREC-II in a recombinant form and generated stably transfected CHO cells to study these interactions at the molecular level and at the cell surface. The SREC-II soluble ectodomain and the cell surface anchored SREC-II entity do not exhibit the same binding properties, rising new hypotheses about its possible biological function
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