Improved anti-IgG and HSA affinity ligands: clinical application of VHH antibody technology.

Large scale, highly specific purification of valuable proteins from blood and removal of undesirable components promise to have wide therapeutic applications. Moreover, depletion of bulk proteins from blood is a prerequisite for clinical proteomics. Here we describe the development of specific, high affinity Camelid antibody fragments (VHH) derived from immune libraries for purification and depletion of the bulk protein HSA and IgG from human serum and plasma for therapeutic and research purposes. The anti-IgG VHH substantially improved depletion of IgGs from blood over the classical method based on protein A. To demonstrate the improved performance of VHH based IgG depletion, we analyzed the presence of auto-antibodies in human plasma before and after depletion from two groups of patients with auto-immune disease: Goodpasture syndrome (GP) and systemic lupus erythematosus (SLE). VHHs can be produced efficiently and cost effectively in Saccharomyces cerevisiae, a genetically regarded as safe (GRAS) microorganism. A good manufacturing process (GMP) for purification of these VHHs has also been developed. Moreover, as VHHs are single protein chains, they can be coupled relatively easily to solid matrices. These three factors are important for developing affinity purification medication.

Quaternary ammonium compounds as water channel blockers. Specificity, potency, and site of action.

Excessive water uptake through Aquaporins (AQP) can be life-threatening and reversible AQP inhibitors are needed. Here, we determined the specificity, potency, and binding site of tetraethylammonium (TEA) to block Aquaporin water permeability. Using oocytes, externally applied TEA blocked AQP1/AQP2/AQP4 with IC50 values of 1.4, 6.2, and 9.8 microM, respectively. Related tetraammonium compounds yielded some (propyl) or no (methyl, butyl, or pentyl) inhibition. TEA inhibition was lost upon a Tyr to Phe amino acid switch in the external water pore of AQP1/AQP2/AQP4, whereas the water permeability of AQP3 and AQP5, which lack a corresponding Tyr, was not blocked by TEA. Consistent with experimental data, multi-nanosecond molecular dynamics simulations showed one stable binding site for TEA, but not tetramethyl (TMA), in AQP1, resulting in a nearly 50% water permeability inhibition, which was reduced in AQP1-Y186F due to effects on the TEA inhibitory binding region. Moreover, in the simulation TEA interacted with charged residues in the C (Asp128) and E (Asp185) loop, and the A(Tyr37-Asn42-Thr44) loop of the neighboring monomer, but not directly with Tyr186. The loss of TEA inhibition in oocytes expressing properly folded AQP1-N42A or -T44A is in line with the computationally predicted binding mode. Our data reveal that the molecular interaction of TEA with AQP1 differs and is about 1000-fold more effective on AQPs than on potassium channels. Moreover, the observed experimental and simulated similarities open the way for rational design and virtual screening for AQP-specific inhibitors, with quaternary ammonium compounds in general, and TEA in particular as a lead compound.