Human heat shock protein 70 (Hsp70) as a peripheral membrane protein.
While a significant fraction of heat shock protein 70 (Hsp70) is membrane associated in lysosomes, mitochondria, and the outer surface of cancer cells, the mechanisms of interaction have remained elusive, with no conclusive demonstration of a protein receptor. Hsp70 contains two Trps, W90 and W580, in its N-terminal nucleotide binding domain (NBD), and the C-terminal substrate binding domain (SBD), respectively. Our fluorescence spectroscopy study using Hsp70 and its W90F and W580F mutants, and Hsp70-∆SBD and Hsp70-∆NBD constructs, revealed that binding to liposomes depends on their lipid composition and involves both NBD and SBD. Association of Hsp70 with phosphatidylcholine (PC) liposomes is weak, with insertion of its Trps into the bilayer hydrocarbon region. In the presence of cardiolipin (CL), bis-monoacylglycero phosphate (BMP), or phosphatidylserine (PS) Hsp70 attaches to membranes peripherally, without penetration. Our data suggest that the organelle distribution of Hsp70 is determined by their specific lipid compositions, with Hsp70 associating with the above lipids in mitochondria, lysosomes, and the surface of cancer cells, respectively. NBD and SBD attach to lipids by extended phospholipid anchorage, with specific acidic phospholipids associating with Hsp70 in the extended conformation with acyl chains inserting into hydrophobic crevices within Hsp70, and other chains remaining in the bilayer. This anchorage is expected to cause a stringent orientation of Hsp70 on the surface. Our data further suggest that acidic phospholipids induce a transition of SBD into the molten globule state, which may be essential to allow SBD-substrate interaction also within the hydrophobic bilayer interior acyl chain region.
Helsinki Biophysics and Biomembrane Group, Department of Biomedical Engineering and Computational Science, Aalto University, Espoo, Finland.
Ajay K
AK
Mahalka
Cell Death and Metabolism, Danish Cancer Society Research Center, Copenhagen, Denmark; Orphazyme ApS, Copenhagen, Denmark.
Thomas
T
Kirkegaard
Helsinki Biophysics and Biomembrane Group, Department of Biomedical Engineering and Computational Science, Aalto University, Espoo, Finland.
Laura T I
LT
Jukola
Cell Death and Metabolism, Danish Cancer Society Research Center, Copenhagen, Denmark.
Marja
M
Jäättelä
Helsinki Biophysics and Biomembrane Group, Department of Biomedical Engineering and Computational Science, Aalto University, Espoo, Finland. Electronic address: paavo.kinnunen@aalto.fi.
Paavo K J
PK
Kinnunen
D002308:Cardiolipins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D008051:Lipid Bilayers / Q000378:metabolism*; D050356:Lipid Metabolism; D008081:Liposomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D008958:Models, Molecular; D010713:Phosphatidylcholines / Q000378:metabolism; D010718:Phosphatidylserines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary
D002308:Cardiolipins; D018840:HSP70 Heat-Shock Proteins; D008051:Lipid Bilayers; D008081:Liposomes; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; D010743:Phospholipids
Extended lipid conformation; Fluorescence; Hsp70; Langmuir-films; Liposomes; Tryptophan