Table 1.

Expression systems available for the production of membrane proteins for NMR spectroscopy

Host organisms	Advantages		Disadvantages
Prokaryotes
Esherichia coli (Gram −)	Rapid. Easy. Scaleable. Cheap. inducible.	Excellent isotope labeling schemes, including for perdeuteration. Various vectors and strains.	Lacking post- translational modifications of higher organisms. Different codon usage.	Prone to inclusion body formation Nonfunctional expression.
Lactoccccus lactis (Gram +)		Increased functional expression. Single membrane.		Isotopic labeling schemes need to be explored. Limited numbers of vectors and strains.
Eukaryotes
Yeast	Functional expression.		Limited post-translational modification available.
Pichia pastoris	Limited post-translational modification.		Potential proteolysis of target proteins.
	Cheap, scalable, inducible.
	Uniform isotopic enrichment methods, including perdeuteration, are available.
Insect cells			Moderately low yields.
Sf9	Compatible post-translational modifications, targeting, insertion and folding.		Post-translational modifications differ from higher organisms. Limited isotope labeling schemes.
S21	High functional expression.		Relatively expensive.
Mammalian cells	Compatible post-translational modifications, targeting, insertion and folding.		Low expression yields.
HEK293			Very limited isotope labeling schemes.
CHO	High functional expression.		Relatively expensive.
	Rapid, easy to control.
	No toxicity.		Expensive.
Cell-free	Versatile labeling incorporation. Scalable.		Limited post-translational modifications unless mammalian microsomes used.