Table 1.

Summary of three commonly used structural determination methods.

Method	Sample Requirement	Advantages	Limitations
NMR	Samples must be in solution	(1) Moelcules are studied in solution (2) Protein folding studies can be done by monitoring NMR spectra (3) Efficient in mapping interactions with other molecules	(1) The upper weight limit for NMR structure determination is ~30 kDa (2) Requires a protein sample be soluble in a high-concentrated solution (3) Overlapped spectrum
X-ray	Samples must be crystallized in a lattice structure	(1) Provides high-resolution information (2) Does not requie a protein be soluble in a high-concentrated solution (3) Applied to proteins or macromolecules in a wide molecular weight range	(1) Requires a protein crystal (2) Crystal contacts can distort protein structure (3) Not suitable with fairly flexible molecules
Cryo-EM	Sample is frozen in its native state	(1) High enough resolution (2) Does not require a protein crystal (3) Does not requie a protein be soluble in a high-concentrated solution	(1) Complex measurements and data analysis (2) Difficult to use for proteins with MW below 300 kDa (3) The technology still needs to be thoroughly tested by the scientific community