Need a reason to switch from Digitonin to GDN?
How about a whole grid box full?

Extracted from the foxglove plant, Digitalis purpurea, Digitonin has been widely used for the solubilization and purification of membrane proteins. In recent years, Digitonin has been used in the Cryo-EM structure determination of membrane proteins, being used in the determination of 6 of the 33 unique membrane protein structures determined by this method. Being a natural product, there are several drawbacks to Digitonin, including batch to batch variability, low solubility, high toxicity, and price.

For years, we’ve been praising the use of glyco-diosgenin (GDN) as a synthetic drop-in substitute for Digitonin ^{(1, 2)}, and we’ve been witnessing its popularity grow substantially. First characterized in 2012, GDN contains a steroid-based hydrophobic group linked to a di-maltose head group (Fig. 1) ⁽³⁾. Both GDN and Digitonin have similar formula weights; however GDN has a much smaller CMC (18 µM) compared to Digitonin (0.5 mM). Being a synthetic compound, there is no batch-to-batch variability, and you don't have to worry about harmful toxic byproducts commonly found in Digitonin such as digitoxin, digoxin, and other cardiac and steroidal glycosides. Add to that a solubility that is >10% in water, and a price that is much lower than Digitonin, and GDN becomes your efficient and cost effective drop-in substitute for Digitonin.

Figure 1: Structure of GDN

In 2017, there were at least three new Cryo-EM structures of membrane proteins which utilized GDN, further supporting the use of GDN as a replacement for Digitonin:

• In June of 2017, the Kobilka and Skiniotis labs at Stanford, ConfometRx, and the University of Michigan published the structure of the activated GLP-1 receptor – G protein complex (PDB: 5VAI)⁽⁴⁾. This complex was solubilized and purified using a mixture of DDM, CHAPS, and CHS, and then exchanged into a mixture of GDN, LMNG, POPG, and Cholesterol for Cryo-EM structure determination.
• In November of 2017, the lab of John Rubinstein at the University of Toronto published the structure of the dimeric Fo region of mitochondrial ATP synthase (PDB: 6B2Z)⁽⁵⁾. For this structure, GDN allowed for the extraction of the dimeric form of ATP synthase from mitochondrial membranes, which is also observed when Digitonin is used. For structure determination by Cryo-EM, 0.02% GDN was used.
• Lastly, in December of 2017, the lab of Andrew Ward at The Scripps Institute published the structure of the mechanically activated ion channel Piezo1 (PDB: 6BPZ)⁽⁶⁾. To prepare this protein for Cryo-EM, membranes were solubilized using CHAPS, soy phosphatidylcholine, and C₁₂E₉. During purification, the detergent was exchanged into 100 µm GDN, concentrated, and spotted onto grids.

 
To build on the excitement from these new structures, we are happy to offer a new 25 gram pack size of GDN, which offers significant savings over our smaller pack sizes. Additionally we’re offering a 5% discount on any purchase of 100 GM of GDN. Contact customer service to find out how to take advantage of this offer and find out how GDN can replace Digitonin in your workflow.

Have a GDN success story to share?  Let us know and we'll be happy to feature your work in an upcoming newsletter!