Molecular motors convert energy into unidirectional mechanical motion. Most biomolecular motors in cells use adenosine triphosphate (ATP) as a chemical energy source. Recently, however, Serratia marcescens chitinase A (SmChiA) has been rediscovered as a molecular motor working in extracellular environments without using ATP. Similar to a monorail car (Fig. 1), SmChiA has cleft-like polysaccharide binding sites and processively hydrolyzes recalcitrant crystalline chitin, a major biomass source, into a water-soluble disaccharide chitobiose. As a tool of biomass conversion to useful chemicals, SmChiA has been extensively studied.