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Structural requirements for lysosomal targeting of the prosaposin precursor protein
Author(s) -
Ham Daniela
Publication year - 2003
Publication title -
cell biology international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.932
H-Index - 77
eISSN - 1095-8355
pISSN - 1065-6995
DOI - 10.1016/s1065-6995(03)00124-0
Subject(s) - biochemistry , chemistry , vesicular transport proteins , c terminus , microbiology and biotechnology , biology , n terminus , peptide sequence , amino acid , gene
Although the Man‐6‐P‐independent lysosomal sorting of prosaposin, a precursor of four saposins (A, B, C, and D) is not understood, a protein/lipid interaction is considered. Immunocytochemical analysis revealed that each single saposin linked to the C‐terminus of prosaposin and to secretory albumin, drives the chimeric protein to lysosomes in COS‐7 cells. Quantitative image analysis demonstrated that saposins are targeted with different efficiency ( P <0.05) and in a less smooth manner than the precursor. Despite a very close homology, the charge distribution at the surface of 3D comparative models between saposins appeared different. Western blotting monitored prosaposin in cells also as a di‐ or trimeric form, whereas the chimeric saposins as monomeric. This implies that each amphipathic saposin‐like motif may be a part of the overall structural requirements for binding of the precursor to the membrane lipids of transport vesicle. The crystal structure of saposin B demonstrating two dimeric units for lipid binding supports current findings.