Dynactin is an essential co-factor for most cellular functions of the microtubule motor cytoplasmic dynein, but the mechanism by which dynactin activates dynein remains unclear. Here, we use single molecule approaches to investigate dynein activation by the dynactin subunit p150Glued. We investigate the formation and motility of a dynein-p150Glued co-complex using dual-color TIRF microscopy. p150Glued recruits and tethers dynein to the microtubule in a concentration-dependent manner. Single molecule imaging of motility in cell extracts demonstrates that the CAP-Gly domain of p150Glued decreases the detachment rate of the dynein-dynactin complex from the microtubule and also acts as a brake to slow the dynein motor. Consistent with this important role, two neurodegenerative disease-causing mutations in the CAP-Gly domain abrogate these functions in our assays. Together, these observations support a model in which dynactin enhances the initial recruitment of dynein onto microtubules and promotes the sustained engagement of dynein with its cytoskeletal track.

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Drying of active pharmaceutical ingredients (APIs) is an energy-intensive process that is often a manufacturing bottleneck due to the relatively long processing times. A key objective is the ability to determine the drying end point, the time at which all solvent has been evaporated from the solid cake. In this contribution, we describe the development and testing of a novel method for determining the end point of pharmaceutical dryers on the basis of online mass spectrometry. The proposed method offers several advantages over existing spectrometric methods, including the ability to detect when the cake is dry from vapor phase measurements and a very simple implementation that does not require chemometric models. The drying end point for each solvent is determined as the time at which the gas phase solvent concentration measurement from the mass spectrometer converges to a predicted value computed from a solvent mass balance in the oven, assuming zero flow rate from the cake. The method is tested on a laboratory-scale vacuum dryer over a range of temperatures and pressures using glass beads with three different particle sizes. Drying end points are automatically detected for acetone, methanol, and methanol−methyl tert-butyl ether (MtBE) solvents well before the unprocessed gas phase solvent concentration measurements suggest that drying is complete. We find that the drying rate increases and the end point is reached more quickly as the mean bead size increases. The method is validated by performing loss on drying experiments for one combination of pressure, temperature, and bead size. Application of the method to an API with methanol−MtBE solvents produced a substantially reduced drying rate compared to that for the glass beads, most likely due to interactions between the API and solvents. We conclude that the proposed method represents a powerful Quality by Design (QbD) approach for pharmaceutical drying processes.

Vacuum drying of active pharmaceutical ingredients (API) is an energy‐intensive process that is often a manufacturing bottleneck. A multiphase transport model to predict drying performance under the assumption that boiling is the dominant mechanism is developed. Laboratory scale drying experiments were performed over a range of temperatures and pressures using acetone as the solvent and glass beads of three different particle sizes to mimic APIs. A two‐phase transport model with the vapor and solid considered as one phase and the liquid treated as the second phase was capable of qualitatively reproducing the drying dynamics is found. Adjustable model parameters estimated from experimental data collected over a range of operating conditions exhibited trends that provided further insight into drying behavior. Boiling is the dominant mechanism in vacuum drying and our transport model captured the key physics of the process. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3639–3655, 2015

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