Extreme-value analysis of intracellular cargo transport by motor proteins.

Abstract

Extreme-value analysis (EVA) deals with deviations of data from the median of probability distributions. It has been used for various purposes, such as predicting disasters and analyzing sports records. Herein, we extended the use of EVA to investigate nanoscale runners within cells. Motor proteins such as kinesin and dynein run along microtubules, which are protein-containing rails, to deliver cargo (material needed for cells). While the velocity of these runners is markedly affected by large cargos in viscous intracellular environments, the return-level EVA plots showed that the velocity near no-load conditions disclosed the physical difference between the two runners, resulting from their load (force)-velocity relationships. The concave-up force-velocity relationship of dynein hampered the independent and identically distributed conditions for the retrograde velocity dataset and the abnormality of the return-level plot of EVA. Our findings underscore the importance of EVA for assessing the physical properties of proteins in vivo.