Fig. 1.

The C-terminal half of coil 2 (Vim2B) shows different folding and unfolding behaviors when unzipped from two different directions. (A) Three-dimensional structural model of a vimentin dimer, save the head and tail domains, provided by A. Chernyatina and S. Strelkov, Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, Katholieke Universiteit Leuven, Leuven, Belgium (7). (Inset) Structural characteristics of the vimentin coil 2B, in which the stutter is highlighted in purple and the conserved region is marked in orange. (B) Schematic of the experimental setup using the Vim2B-N construct as an example. (C) Representative stretch-and-relax cycle recorded at 500 nm/s for Vim2B-N. Black arrows indicate the two major transitions. (D) Traces recorded in passive mode show equilibrium fluctuations between an intermediate and the unfolded state of Vim2B-N at varying force bias. The CC fluctuates between states mostly residing in the lower unfolded state at higher force bias (Top) and more in the upper partly folded state for decreasing force bias (Middle and Bottom). Full-bandwidth traces (100 kHz) are gray and low-pass filtered traces are colored in red. (E) A representative force-extension trace for Vim2B-C shows a clear three-state behavior (intermediate marked by an arrow). (F) Fluctuations between all three states of the Vim2B-C coil may be monitored in passive mode at a force bias of about 9.1 pN. (Inset) Transition between the folded and intermediate states (intermediate states are marked by an arrow). Full-bandwidth traces (100 kHz) are gray, whereas low-pass filtered traces are colored in green.