Characterization of apolipoprotein A-I structure using a cysteine-specific fluorescence probe.
Two new Cys mutants of proapolipoprotein A-I, D9C and A232C, were created and expressed in Escherichia coli systems. Specific labeling with the thiol-reactive fluorescence probe, 6-acryloyl-2-dimethylaminonaphthalene (acrylodan), was used to study the structural organization and dynamic properties of the extreme regions of human apolipoprotein A-I (apoA-I) in lipid-free and lipid-bound states. Spectroscopic approaches, including circular dichroism and various fluorescence methods, were used to examine the properties of the mutant proteins and of their covalent adducts with the fluorescence probe. The mutations themselves had no effect on the structure and stability of apoA-I in the lipid-free state and in reconstituted HDL (rHDL) complexes. Furthermore, covalent modification with acrylodan did not alter the properties of the apoA-I variants in the lipid-bound state nor in the lipid-free A232C mutant, but it affected the structure and local stability of the lipid-free protein in the D9C mutant. Fluorescence results using the acrylodan probe confirmed a well-organized structure in the N-terminal region of apoA-I. Also, they suggested a three-dimensional structure in the C-terminal region, stabilized by protein-protein contacts. When Trp residues and acrylodan were used as donor-acceptor pairs for fluorescence resonance energy transfer (FRET), average distances could be measured. Both intensity and lifetime changes of the Trp emission indicated a protein folding in solution that brings the C-terminus of the protein near the Trp residues in the N-terminal half of the sequence. Also, the N- and C-terminal domains of apoA-I appeared to be near each other in rHDL having two apoA-I per particle.
Tricerri
M A
MA
Department of Biochemistry and Laboratory for Fluorescence Dynamics, University of Illinois at Urbana-Champaign Urbana, Illinois 61801, USA.
Behling Agree
A K
AK
Sanchez
S A
SA
Jonas
A
A
D015081:2-Naphthylamine / Q000031:analogs & derivatives* / Q000378:metabolism; D016632:Apolipoprotein A-I / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D001054:Apolipoproteins A / Q000737:chemistry / Q000235:genetics; D003545:Cysteine / Q000235:genetics / Q000378:metabolism*; D004735:Energy Transfer; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes / Q000378:metabolism*; D006801:Humans; D050356:Lipid Metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000737:chemistry; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics; D017434:Protein Structure, Tertiary / Q000235:genetics; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D005456:Fluorescent Dyes; D008075:Lipoproteins, HDL; D010446:Peptide Fragments; D020033:Protein Isoforms; D011498:Protein Precursors; D011994:Recombinant Proteins; C038518:acrylodan; D015081:2-Naphthylamine; D003545:Cysteine