Microviscosity in E. coli Cells from Time-Resolved Linear Dichroism Measurements.

Area of Science:

• Biophysics
• Cell Biology
• Spectroscopy

Background:

• Protein function is influenced by cellular microviscosity, the viscosity relevant to molecular motion.
• Macromolecular crowding in cells creates a complex viscous environment.
• Time-resolved linear dichroism (TRLD) spectroscopy is a sensitive method for measuring microviscosity.

Purpose of the Study:

• To measure the microviscosity experienced by myoglobin within the heterogeneous cytoplasm of E. coli.
• To assess the utility of TRLD spectroscopy for probing intracellular viscosity.
• To gain insights into the nature of the cellular environment through protein mobility.

Main Methods:

• Utilized quasi-null, ultrasensitive time-resolved linear dichroism (TRLD) spectroscopy.
• Measured rotational diffusion times of photolyzed deoxyhemoglobin (deoxyMb) ensembles in E. coli cytoplasm.
• Compared in vivo TRLD measurements with previous in vitro studies.

Main Results:

• The rotational diffusion of deoxyMb ensembles in E. coli cytoplasm occurred with a lifetime of 34 ± 6 ns.
• This diffusion time corresponds to an intracellular microviscosity of 2.82 ± 0.42 centipoise (cP).
• The measured microviscosity is consistent with previously reported values for E. coli cytoplasmic viscosity.

Conclusions:

• TRLD spectroscopy successfully measured myoglobin mobility and intracellular microviscosity in E. coli.
• The findings provide valuable data on the cytoplasmic environment and protein mobility within living cells.
• TRLD spectroscopy is demonstrated as a feasible technique for probing intracellular viscosity.