DOGS-NTA-Ni is a synthetic diacyl lipid with a His-tag binding head group. In my opinion, the easier way to incorporate it into liposomes is at the start when everything is dissolved together. The resulting liposomes should have the DOGS-NTA-Ni evenly distributed. One problem with adding it to preformed liposomes is that it will have to be dissolved in either detergent or organic solvent, so that your final product will have residual detergent or solvent. If you want to remove it, you will have to add another step to the preparation. Another problem is that some or all of the DOGS-NTA-Ni you add may not incorporate and may just precipitate. It definitely will not covalently bind to the other lipids in the liposome without some sort of deliberate chemical crosslinking procedure.

DOGS-NTA-Ni is a synthetic diacyl lipid with a His-tag binding head group. In my opinion, the easier way to incorporate it into liposomes is at the start when everything is dissolved together. The resulting liposomes should have the DOGS-NTA-Ni evenly distributed. One problem with adding it to preformed liposomes is that it will have to be dissolved in either detergent or organic solvent, so that your final product will have residual detergent or solvent. If you want to remove it, you will have to add another step to the preparation. Another problem is that some or all of the DOGS-NTA-Ni you add may not incorporate and may just precipitate. It definitely will not covalently bind to the other lipids in the liposome without some sort of deliberate chemical crosslinking procedure.

Thank you for your response, Dr. Shapiro. 

You mentioned in your answer that DOGS-NTA-Ni should not be directly added to a pre-formed liposome. Is this because the bond is not strong enough, so the DOGS-NTA-Ni will just precipitate? Additionally, I was wondering, based on your statement, if there was any other way to attach DOGS-NTA-Ni to a liposome without having to mix it in the beginning. For example, is there another substance that can strongly attach the preformed liposome with the DOGS-NTA-Ni? If not, what is the best way to bond his-tagged proteins (such as E-selectin) to a liposome? I was using DOGS-NTA-Ni to achieve this, but is there any other method?

To add to what Adam well stated: If you want to prepare good liposomes with your desired lipid composition, you need to include DOGS-NTA-Ni with your lipids from the beginning - mix all of your compounds in an organic solvent, evaporate the solvent and add your buffer/water and adjust the DOGS-NTA-Ni containing liposomes to a desired size by freeze-thawing, extrusion and/or sonication. Strictly speaking, there is no "binding" of any kind going on, rather the "DOGS" becomes part of the liposome via the hydrophobic effect, just like cholesterol and the hydrocarbon tails of your phospholipids, since it essentially acts like a lipid. The "NTA-Ni" then again acts similarly to a polar lipid headgroup and resides on the inner and outer surface of your liposome. If you want to add the DOGS-NTA-Ni to preformed liposomes it will probably not work or will be an unpractically slow process. Using detergents might help, but as Adam already mentioned, you won't be able to remove all of your detergent after the process. I take it that you would like to prepare liposomes with DOGS-NTA-Ni only on the outer liposome layer?

Cheers,

Arne

May I know what could be an ideal lipid composition to make liposomes incorporated with DOGS-NTA-Ni. I want to attach my his tag proteins on to it for enzyme assay. TIA Roy Ghosh Adam B Shapiro Arne Raasakka

Hi Dhanaraju,

essentially anything with dioleoyl tails as DOGS contain the same tails. DOPE and DOPC as neutral zwitterionic lipids and DOPS or DOPG as negatively charged ones. The ratio of these depend a lot on the biological compartment you want to mimic. Remember that Ni2+ and other divalent cations (Ca2+ and Mg2+ notably) and/or your protein might have (un)specific affinity for the negative charged ones. Otherwise these lipid types tend to behave quite nice as liposomes when made smaller by extrusion or sonication. You can also include a moderate amount of cholesterol (10-30 m-%) if you wish without major problems.

Hope this helps and happy holidays,

Arne

Thanks @ArneRaasakka