Dissecting the\npH Sensitivity of Kinesin-Driven Transport

Kinesin-1 is a crucial motor protein that drives the\nmicrotubule-based\nmovement of organelles, vital for cellular function and health. Mostly\nstudied at pH 6.9, it moves at approximately 800 nm/s, covers about\n1 μm before detaching, and hydrolyzes one ATP per 8 nm step.\nGiven that cellular pH is dynamic and alterations in pH have significant\nimplications for disease, understanding how kinesin-1 functions across\ndifferent pH levels is crucial. To explore this, we executed single-molecule\nmotility assays paired with precise optical trapping techniques over\na pH range of 5.5–9.8. Our results show a consistent positive\nrelationship between increasing pH and the enhanced detachment (off\nrate) and speed of kinesin-1. Measurements of the nucleotide-dependent\noff rate show that kinesin-1 exhibits the highest rate of ATPase activity\nat alkaline pH, while it demonstrates the optimal number of ATP turnover\nand cargo translocation efficiency at the acidic pH. Physiological\npH of 6.9 optimally balances the biophysical activity of kinesin-1,\npotentially allowing it to function effectively across a range of\npH levels. These insights emphasize the crucial role of pH homeostasis\nin cellular function, highlighting its importance for the precise\nregulation of motor proteins and efficient intracellular transport.