The di-leucine motif contributes to class a scavenger receptor-mediated internalization of acetylated lipoproteins.
OBJECTIVE
The di-leucine motif exists in the intracellular domains of certain cell surface receptors, participating in the receptor-mediated endocytosis. The present study was aimed at determining the role of the di-leucine motif in class A scavenger receptor (SR-A)-mediated ligand endocytosis.


RESULTS
cDNA coding for a mutant (SR-A mutant N3132LM) with deletion of the di-leucine structure was transfected into Chinese hamster ovary (CHO) cells. Compared with wild-type SR-A-expressing cells, the cells expressing the SR-A mutant N3132LM showed a significant decrease in uptake but almost no change in binding of the SR-A ligand acetylated low-density lipoprotein (AcLDL). Western blot analysis revealed coimmunoprecipitation of SR-A mutant and clathrin from the lysates of the mutant but not wild-type CHO cells, suggesting that AcLDL-bound SR-A mutant N3132LM is associated with the clathrin-coated pit of cellular membrane. Removal of the first 27 amino acid residues from the SR-A N-terminus further reduced AcLDL uptake by the cells with the di-leucine motif mutation.


CONCLUSIONS
The di-leucine motif of SR-A intracellular domain contributes to the SR-A-mediated cellular internalization of AcLDL. Di-leucine pair exists in the cytoplasmic domain of class A scavenger receptor. The cells expressing di-leucine mutants showed decreased uptake and unchanged binding of AcLDL. The di-leucine pair was not associated to coated pits. It suggests that di-leucine motif acts as a signal sequence to mediate SR-A into cell.
Institute of Reproductive Medicine, Nanjing Medical University, Nanjing, People's Republic of China.
Yaoyu
Y
Chen
Xiaohua
X
Wang
Jingjing
J
Ben
Shen
S
Yue
Hui
H
Bai
Xiaoxiang
X
Guan
Xiaoming
X
Bai
Li
L
Jiang
Yong
Y
Ji
Leming
L
Fan
Qi
Q
Chen
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D002966:Clathrin / Q000378:metabolism; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003593:Cytoplasm; D004705:Endocytosis; D008024:Ligands; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D017434:Protein Structure, Tertiary; D051117:Scavenger Receptors, Class A / Q000235:genetics / Q000502:physiology*; D014162:Transfection
D002966:Clathrin; D008024:Ligands; D008077:Lipoproteins, LDL; D051117:Scavenger Receptors, Class A; C032629:acetyl-LDL