New BODIPY lipid probes for fluorescence studies of membranes.
Many fluorescent lipid probes tend to loop back to the membrane interface when attached to a lipid acyl chain rather than embedding deeply into the bilayer. To achieve maximum embedding of BODIPY (4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) fluorophore into the bilayer apolar region, a series of sn-2 acyl-labeled phosphatidylcholines was synthesized bearing 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indacene-8-yl (Me(4)-BODIPY-8) at the end of C(3)-, C(5)-, C(7)-, or C(9)-acyl. A strategy was used of symmetrically dispersing the methyl groups at BODIPY ring positions 1, 3, 5, and 7 to decrease fluorophore polarity. Iodide quenching of the phosphatidylcholine probes in bilayer vesicles confirmed that the Me(4)-BODIPY-8 fluorophore was embedded in the bilayer. Parallax analysis of Me(4)-BODIPY-8 fluorescence quenching by phosphatidylcholines containing iodide at different positions along the sn-2 acyl chain indicated that the penetration depth of Me(4)-BODIPY-8 into the bilayer was determined by the length of the linking acyl chain. Evaluation using monolayers showed minimal perturbation of <10 mol% probe in fluid-phase and cholesterol-enriched phosphatidylcholine. Spectral characterization in monolayers and bilayers confirmed the retention of many features of other BODIPY derivatives (i.e., absorption and emission wavelength maxima near 498 nm and approximately 506-515 nm) but also showed the absence of the 620-630 nm peak associated with BODIPY dimer fluorescence and the presence of a 570 nm emission shoulder at high Me(4)-BODIPY-8 surface concentrations. We conclude that the new probes should have versatile utility in membrane studies, especially when precise location of the reporter group is needed.
Boldyrev
Ivan A
IA
Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997 Russia.
Zhai
Xiuhong
X
Hormel Institute, University of Minnesota, Austin, MN 55912.
Momsen
Maureen M
MM
Hormel Institute, University of Minnesota, Austin, MN 55912.
Brockman
Howard L
HL
Hormel Institute, University of Minnesota, Austin, MN 55912.
Brown
Rhoderick E
RE
Hormel Institute, University of Minnesota, Austin, MN 55912.
Molotkovsky
Julian G
JG
Shemyakin and Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, 117997 Russia.
D001896:Boron Compounds; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D005456:Fluorescent Dyes; D008051:Lipid Bilayers / Q000737:chemistry*; D008563:Membrane Lipids / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D053835:Unilamellar Liposomes / Q000737:chemistry
C095489:4,4-difluoro-4-bora-3a,4a-diaza-s-indacene; D001896:Boron Compounds; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D008563:Membrane Lipids; D010713:Phosphatidylcholines; D053835:Unilamellar Liposomes