Interaction of N-methyl-anthraniloyl-labelled porcine apolipoprotein A-I with porcine lecithin: cholesterol acyltransferase: an energy transfer study.
1. To investigate whether a direct protein-protein interaction between apoA-I and lecithin:cholesterol acyltransferase (LCAT) is necessary for the activation of the enzyme, apoA-I was labelled with N-methylisatoic anhydride at lysine residues. The intermolecular resonance energy transfer from tryptophan residues of LCAT (donor) to N-methyl-anthraniloyl (NMA)-labelled apoA-I (NMA-apoA-I) (acceptor) was used as a sensitive fluorescence method for studying molecular interactions. 2. In the absence of lipids no fluorescence energy transfer was measurable. 3. Fluorescence energy transfer occurred from LCAT to NMA-apoA-I in the presence of liposomes with phospholipid/cholesterol ratios ranging from 5:1 to 18:1 and regardless whether only 1 or up to 5 NMA-apoA-I molecules resided at the liposome surface. 4. This indicates a preferred binding of the enzyme directly to or in spatial proximity to the activator protein NMA-apoA-I even if enough space at the liposome surface is available to allow LCAT binding at a distance, where no energy transfer is measurable.
Knipping
G
G
Institute of Medical Biochemistry, University of Graz, Austria.
Hermetter
A
A
Hubmann
M R
MR
D000812:Anhydrides / Q000737:chemistry*; D000818:Animals; D016632:Apolipoprotein A-I / Q000737:chemistry / Q000378:metabolism*; D004735:Energy Transfer; D004789:Enzyme Activation; D008081:Liposomes / Q000378:metabolism; D008239:Lysine / Q000737:chemistry; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013552:Swine; D062367:ortho-Aminobenzoates / Q000737:chemistry*
D000812:Anhydrides; D016632:Apolipoprotein A-I; D008081:Liposomes; D062367:ortho-Aminobenzoates; C077537:N-methylisatoic anhydride; D007862:Phosphatidylcholine-Sterol O-Acyltransferase; D008239:Lysine