The Effect of Shear on the Structural Conformation of rhGH and IgG1 in Free Solution

The effect of hydrodynamic forces on proteins in free solution, also referred to as shear stress in multiple drug substance and drug product processing steps, was investigated by means of in situ and inline biophysical measurements. The use of a quartz Couette cell in combination with a circular dichroism spectrometer allowed simultaneously the creation of simple shear flow and direct measurements of the proteins' secondary and tertiary structure. Recombinant human growth hormone and an IgG1 mAb were chosen as model proteins. Under the exclusion of interfacial effects by the addition of a surfactant, no unfolding was observed due to shearing for 30 min up to the highest possible shear rate under laminar flow (3840 s−1). In another experiment, guanidine hydrochloride was added to a surfactant-protected and sheared sample to lower the thermodynamic and mechanical stability of the proteins. However, even under these destabilizing conditions, the proteins showed no change in their secondary and tertiary structure. We conclude that shear stress in terms of velocity gradients is unlikely to unfold the investigated proteins in free solution up to shear rates of at least 104 s−1.