Mortalin/GRP75 binds to complement C9 and plays a role in resistance to complement-dependent cytotoxicity.
Mortalin/GRP75, the mitochondrial heat shock protein 70, plays a role in cell protection from complement-dependent cytotoxicity (CDC). As shown here, interference with mortalin synthesis enhances sensitivity of K562 erythroleukemia cells to CDC, whereas overexpression of mortalin leads to their resistance to CDC. Quantification of the binding of the C5b-9 membrane attack complex to cells during complement activation shows an inverse correlation between C5b-9 deposition and the level of mortalin in the cell. Following transfection, mortalin-enhanced GFP (EGFP) is located primarily in mitochondria, whereas mortalinΔ51-EGFP lacking the mitochondrial targeting sequence is distributed throughout the cytoplasm. Overexpressed cytosolic mortalinΔ51-EGFP has a reduced protective capacity against CDC relative to mitochondrial mortalin-EGFP. Mortalin was previously shown by us to bind to components of the C5b-9 complex. Two functional domains of mortalin, the N-terminal ATPase domain and the C-terminal substrate-binding domain, were purified after expression in bacteria. Similar to intact mortalin, the ATPase domain, but not the substrate-binding domain, was found to bind to complement proteins C8 and C9 and to inhibit zinc-induced polymerization of C9. Binding of mortalin to complement C9 and C8 occurs through an ionic interaction that is nucleotide-sensitive. We suggest that to express its full protective effect from CDC, mortalin must first reach the mitochondria. In addition, mortalin can potentially target the C8 and C9 complement components through its ATPase domain and inhibit C5b-9 assembly and stability.
From the Departments of Cell and Developmental Biology, Sackler School of Medicine and.
Moran
M
Saar Ray
From the Departments of Cell and Developmental Biology, Sackler School of Medicine and.
Oren
O
Moskovich
Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
Ohad
O
Iosefson
From the Departments of Cell and Developmental Biology, Sackler School of Medicine and lifish@post.tau.ac.il.
Zvi
Z
Fishelson
D000244:Adenosine Diphosphate / Q000276:immunology / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000276:immunology / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000276:immunology / Q000494:pharmacology; D001665:Binding Sites / Q000235:genetics / Q000276:immunology; D015153:Blotting, Western; D003186:Complement C9 / Q000276:immunology* / Q000378:metabolism; D015938:Complement Membrane Attack Complex / Q000276:immunology / Q000378:metabolism; D003165:Complement System Proteins / Q000276:immunology* / Q000378:metabolism; D003602:Cytotoxicity, Immunologic / Q000276:immunology*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000276:immunology* / Q000378:metabolism; D006801:Humans; D020014:K562 Cells; D018613:Microscopy, Confocal; D011485:Protein Binding / Q000187:drug effects / Q000276:immunology; D034622:RNA Interference; D012965:Sodium Chloride / Q000276:immunology / Q000494:pharmacology
D003186:Complement C9; D015938:Complement Membrane Attack Complex; D018840:HSP70 Heat-Shock Proteins; C080352:mortalin; D049452:Green Fluorescent Proteins; D012965:Sodium Chloride; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D003165:Complement System Proteins; D000251:Adenosine Triphosphatases
C5b-9; Complement System; GRP75; Heat Shock Protein; Immunology; Molecular Chaperone; Mortalin; Necrosis (Necrotic Death)