  We introduce a model for stochastic transport on a one-dimensional substrate
with particles assuming different conformations during their stepping cycles.
These conformations correspond to different footprints on the substrate: in
order to advance, particles are subject to successive contraction and expansion
steps with different characteristic rates. We thus extend the paradigmatic
exclusion process, provide predictions for all regimes of these rates that are
in excellent agreement with simulations, and show that the current-density
relation may be affected considerably. Symmetries are discussed, and exploited.
We discuss our results in the context of molecular motors, confronting a
hand-over-hand and an inchworm stepping mechanism, as well as for ribosomes.
