Complement factor 5a receptor chimeras reveal the importance of lipid-facing residues in transport competence.
Complement factor 5a receptor chimeras reveal the importance of lipid-facing residues in transport competence.
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DOI：
10.1111/j.1742-4658.2009.07002.x
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发表时间：
2009-05
期刊：
影响因子：
--
通讯作者：
Baranski TJ
中科院分区：
文献类型：
--
作者：
Klco JM;Sen S;Hansen JL;Lyngsø C;Nikiforovich GV;Sheikh SP;Baranski TJ
Residues that mediate helix-helix interactions within the seven transmembranes (TM) of G protein-coupled receptors are important for receptor biogenesis and the receptor switch mechanism. In contrast, the residues directly contacting the lipid bilayer have only recently garnered attention as potential receptor dimerization interfaces. In this study we sought to determine the contributions of these lipid-facing residues to receptor function and oligomerization by systemically generating chimeric C5a receptors in which the entire lipid-exposed surface of a single TM helix was exchanged with the cognate residues from the angiotensin AT1 receptor. Disulfide-trapping and BRET studies demonstrated robust homodimerization of both C5a receptor and AT1R, but no evidence for heterodimerization. Despite relatively conservative substitutions, the lipid-facing chimeras (TM 1, 2, 4, 5, 6, or 7) were retained in the ER/cis-Golgi network. With the exception of the TM7 chimera that did not bind ligand, the lipid-facing chimeras bound ligand with low affinity, but similar to wild-type C5a receptors trapped in the ER with Brefeldin A. These results suggest that the chimeric receptors were properly folded; moreover, native C5a receptors are not fully competent to bind ligand when present in the ER. BRET oligomerization studies demonstrated energy transfer between the wild-type C5aR and the lipid-facing chimeras suggesting that the lipid-facing residues within a single TM segment are not essential for oligomerization. These studies highlight the importance of the lipid-facing residues in C5a receptor for transport competence.
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