Protein solutions in research and development

Determination of protein structure is a top priority for complete understanding of the role and function of many proteins. One indicator of protein structure is the size of the molecule. Dynamic light scattering (DLS) can rapidly determine the size of a protein and estimate the molecular weight using an accepted calibration technique. A list of a few common examples are:

Protein	Hydrodynamic radius, RH in nm	Molecular Weight from DLS, in kDa	Known MW in kDa
Lysozyme	1.9	15.1	14.7
Chymotrypsinogen	2.4	26.1	25
Human Insulin (pH7)	2.7	34.4	34.2
Ovalbumin	3.0	44	43
Hemoglobin	3.5	63	65
Bovine Serum Albumin	3.6	66	67
Hexokinase	4.3	102	102
Apoferritin	8.2	463	443
Thyroglobulin	10.1	754	669

For a number of proteins this rapid method is a convenient route to obtain an indication of the quaternary structure. For example human insulin with a monomer of 5.7kDa shows a hydrodynamic radius suggesting a molecular weight of 34.4kDa – which is consistent with a hexameric conformation and in agreement with protein crystallography.

Many proteins show profound changes in different solution conditions, with the most extreme structure change being thermal denaturation. When a protein is heated above its melting point, significant unfolding leads to exposed hydrophobic chains and can cause severe, and nonreversible aggregation. Again, dynamic light scattering is ideal for studying the protein melting point phenomenon as the technique is exquisitely sensitive to large scattering objects such as aggregates and thermal denatured protein. Similar structure changes may happen over time, pH, ionic strength and changes in various other solution conditions, and dynamic light scattering again is an ideal tool to quickly assess the condition of the molecule in solution.

	Protein case studies:
	Crystal screening.
	Protein melting point.
	Protein formulation stability.