Biophysics of Single Motor Proteins

Stepping of Motor Proteins along Microtubules

(Processive) microtubule motors are characterised by their speed, their run length and their directionality. We are interested in studying the structural determinants for these motor properties as well as the influence of the environment on the stepping process. In particular, we use 2D and 3D nanometer imaging (employing fluorescent markers such as fluorescent proteins and quantum dots as well as scattering gold nano-particles) to investigate (i) the detailed path of motors on the microtubule surface, i.e. if they follow - or switch between - single protofilaments (Nitzsche 2008, Bormuth 2012), (ii) the influence of post-translational tubulin modifications (Walter 2012), (iii) the impact of molecular crowding (Leduc 2012), as well as (iv) the behaviour of the motors upon encountering roadblocks/obstacles (Korten 2008, Schneider 2015). Movie: In vitro stepping motility of a single GFP-labeled kinesin-1 motor (green) stepping along a rhodamine-labeled microtubule (red). (See also Helenius 2006, Varga 2009, Gell 2010, Korten 2011.)

Diffusion of Motor Proteins and Crosslinkers on Microtubules

Besides directed movement, motor proteins and other microtubule-associated proteins (MAPs) can perform diffusive motion along microtubules. For example, the mitotic centromere associated kinesin (MCAK) uses one-dimensional diffusion along the microtubule lattice to efficiently target the microtubule ends where it acts as depolymerase (Helenius 2006). Other motors (e.g. kinesin-14) and passive crosslinkers (e.g. Ase1) use diffusive binding sites to bundle microtubules (Fink 2009, Braun 2011). We are interested to study the diffusion constants (and the related friction coefficients) of these proteins under varying buffer and crowding conditions. Movie: In vitro diffusive motility of single GFP-labeled kinesin-14 motor tails (green) stepping along a rhodamine-labeled microtubule (red).