title: Observation of individual microtubule motor steps in living cells with endocytosed quantum dots.
abstract: We report the observation of individual steps taken by motor proteins in living cells by following movements of endocytic vesicles that contain quantum dots (QDs) with a fast camera. The brightness and photostability of quantum dots allow us to record motor displacement traces with 300 micros time resolution and 1.5 nm spatial precision. We observed individual 8 nm steps in active transport toward both the microtubule plus- and minus-ends, the directions of kinesin and dynein movements, respectively. In addition, we clearly resolved abrupt 16 nm steps in the plus-end direction and often consecutive 16 nm and occasional 24 nm steps in minus-end directed movements. This work demonstrates the ability of the QD assay to probe the operation of motor proteins at the molecular level in living cells under physiological conditions.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Xiaolin
authors.initials: X
authors.lastname: Nan
authors.forename: Peter A
authors.initials: PA
authors.lastname: Sims
authors.forename: Peng
authors.initials: P
authors.lastname: Chen
authors.forename: X Sunney
authors.initials: XS
authors.lastname: Xie
mesh_terms: D045744:Cell Line, Tumor; D003593:Cytoplasm / Q000502:physiology / Q000648:ultrastructure; D004705:Endocytosis / Q000502:physiology*; D006801:Humans; D008870:Microtubules / Q000502:physiology* / Q000648:ultrastructure; D020409:Molecular Motor Proteins / Q000502:physiology* / Q000648:ultrastructure; D045663:Quantum Dots; D022161:Transport Vesicles / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D020409:Molecular Motor Proteins