Figure 1.

TNF-α’s monomerization and re-trimerization kinetics. TNF-α-DNA conjugates were immobilized by hybridization to surface-tethered complementary DNA strands, monomerized by buffer flow and subsequently re-trimerized (A). By measurement of the hydrodynamic diameter, the size of immobilized TNF-α (t0), monomerized complexes (t1), and complexes subjected to free TNF-α in nanomolar concentrations (tEND) was determined (B). In the initial state, size determination of immobilized TNF-α yields a hydrodynamic diameter of 5.6 ± 0.1 nm, whereas after 2000 s of buffer flow a smaller size, corresponding to monomeric TNF-α of 3.9 ± 0.1 nm is determined. Injection of higher nanomolar concentrations of free TNF-α induced efficient trimer formation, rendering the transition a reversible process. A single exponential fit of the monomerization kinetics yields a monomerization rate of 1.66 ± 0.25 E-3 s-1(C, solid orange line, t0 to t1). High nanomolar concentrations of free TNF-α led to fast re-trimerization within less than 600 s (C, t1 to tEND).