Alabaster, AL 35007
1-800-227-0651 or 205-663-2494
Fax 1-800-229-1004 or 205-663-0756
Orders:
Technical Questions:
General Information:
|
Synthetic Products
|
|
| Magnetic Alignment |
|
(DMPE DTPA)
|
|
1,2-Dimyristoyl-sn-Glycero-3-PhosphoEthanolamineDiethyleneTriaminePentaAcetate
|
| Blue, green, and red stylized molecules represent DMPC, DMPG, and DMPEDTPA, respectively. Yellow represents the Yb3+ ion. DHPC, which is believed to be sequestered in curvature defect regions, is not shown in this figure. We thank Biophysical Journal for permission to use this graphic. |
||||||||||||||||||||||
| Magnetic Alignment of Biological Membranes | ||||||||||||||||||||||
| A phospholipid chelate complexed with ytterbium (DMPEDTPA:Yb3+) is shown to be readily incorporated into a model membrane system, which may then be aligned in a magnetic field such that the average bilayer normal lies along the field. This socalled positively ordered smectic phase, whose lipids consist of less than 1% DMPEDTPA:Yb3+, is ideally suited to structural studies of membrane proteins by solidstate NMR, lowangle diffraction, and spectroscopic techniques that require oriented samples. The chelate, DMPE-DTPA:Yb3+, which strongly binds the lanthanide ions and serves to orient the membrane in a magnetic field, prevents direct lanthanideprotein interactions and significantly reduces paramagnetic shifts and line broadening. The greatest advantage of the positively aligned lanthanide-chelate membranes lies in their application to the study of large immobile membrane proteins. Similar lowspin lanthanide chelates may have applications in fieldordered solution NMR studies of watersoluble proteins and in the design of new magnetically aligned liquid crystalline phases. | ||||||||||||||||||||||
Phospholipids used in Magnetic Alignment of Biological Membranes |
||||||||||||||||||||||
|
||||||||||||||||||||||
| The model membrane consisting of the phospholipids
DMPC and DHPC, in combination with the negatively charged lipid, DMPG,
and a minimal concentration of DMPEDTPA chelate, complexed with equimolar
Yb3+, results in a stable positively aligned bilayer phase
suitable for membrane protein studies. The authors typically use either
a 25% aqueous (w/w) dispersion of DMPC/DHPC/DMPG/DMPEDTPA:Yb3+
in a 2.75/1.00/0.1375/0.0306 mole ratio or a 40% (w/w) aqueous dispersion
of DMPC/DHPC/DMPG/DMPEDTPA:Yb3+ in a 2.75/0.458/0.1375/0.0306
mole ratio; the 25% mixture often results in the best linewidths,
whereas the latter combination yields larger order parameters and
chemical shift offsets. The addition of peptide often necessitates
higher lanthanide concentrations to maintain alignment. In such cases,
the chelate is expected to be essential in sequestering the lanthanides
away from the protein or molecule of interest and minimizing paramagnetic
broadening. Both 31P and 13C NMR spectra reveal
that the DMPEDTPA chelate, in combination with minimal concentrations
of Yb3+, significantly reduces paramagnetic shifts and
broadening in both lipid and peptide spectra. The minimal Yb3+
concentration for positive alignment in the presence of equimolar
chelate is observed to be ~25% smaller (i.e., Yb3+/DMPC = 0.008 with
chelate versus Yb3+/DMPC = 0.010 without chelate). Furthermore,
the use of negatively charged lipid and chelate stabilizes the liquid
crystalline phase as a function of temperature and seems to prevent
longterm sample degradation. The use of negatively charged lipid in
combination with the chelate is essential.
Reference.
|
||||||||||||||||||||||
