- Kenji Akasaki (Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University / email@example.com)
Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University
Lysosome-associated membrane protein-1 (LAMP-1) is a type I membrane glycoprotein consisting of a large luminal domain, a membrane-anchoring domain, and a short cytoplasmic tail (CT). The tyrosine-based motif (G378Y379QTI382) in its CT exclusively binds to adapter protein complex-3 (AP-3), which may facilitate the incorporation of LAMP-1 into transport vesicles to late endosomes and lysosomes. Of this sequence, Y379 is critical, and hydrophobic I382 is optimal for the AP-3 binding and the efficient delivery to lysosomes. However, it is not clear how important G378 is in the AP-3 binding and lysosome transport. To clarify its importance, four mutants in which G378 was replaced with alanine, aspartic acid, glutamic acid, and asparagine (designated as G378A, G378D, G378E, and G378N, respectively) were prepared and their interaction strengths with AP-3 and lysosomal abundance were compared with those of wild-type (WT)-LAMP-1. A yeast two-hybrid system was applied to measure the interaction strengths of WT-, G378A-, G378D-, G378E-, and G378N-CTs with the medium subunit of AP-3 (μ3A). The G378A-, G378D-, and G378E-CTs as strongly interacted with μ3A as WT-CT, but the G378N-CT exhibited a very weak interaction with it. In the cell fractionation analyses, the lysosomal levels of G378A, G378D, and G378E were almost the same as that of WT whereas a lesser amount of G378N existed in the lysosomes. Taken together, it is considered that Y379 and I382 are essential for AP-3-mediated vesicular transport of LAMP-1 while the Y379-preceding amino acid is not restricted to glycine but asparagine at this position is less suitable for that.