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Single-molecule study of molecular mobility in the cytoplasm of Escherichia coli

Yoriko Lill, Wallace A. Kaserer, Salete M. Newton, Markus Lill, Phillip E. Klebba, and Ken Ritchie
Phys. Rev. E 86, 021907 – Published 9 August 2012
Physics logo See Synopsis: Tracking the Movement of Single Molecules in Cells

Abstract

The cytoplasm of bacterial cells is filled with individual molecules and molecular complexes that rely on diffusion to bring them together for interaction. The mobility of molecules in the cytoplasm has been characterized by several techniques mainly using fluorescent probes and ensemble methods. In order to probe the microenvrionment inside the cytoplasm as viewed by an individual molecule, we have studied single green fluorescent proteins (GFPs) diffusing in the cytoplasm of Escherichia coli cells at observation at rates ranging from 60 to 1000 Hz. Over long times the diffusion shows confinement due to the geometry of the cells themselves. A simulation in model cells using the actual distribution of cell sizes found in the experiments describes accurately the experimental results as well as reveals a short time diffusion coefficient that agrees well with that determined by ensemble methods. Higher short time diffusion coefficients can be obtained by filling the simulated cell with small spheres modeling cytoplasmic molecules and, depending on the density of particles included in the modeled cytoplasm, can approach the diffusion coefficient of GFPs found in water. Thus, single-molecule tracking combined with analysis using simple simulation of Brownian motion is able to reveal the main contributors to the GFP mobility in the cytoplasm of E. coli.

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  • Received 18 November 2011

DOI:https://doi.org/10.1103/PhysRevE.86.021907

©2012 American Physical Society

Synopsis

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Tracking the Movement of Single Molecules in Cells

Published 9 August 2012

Fluorescence imaging of single molecules combined with computer simulations suggest that a crowded cytoplasm may reduce the measured protein mobility in cells.

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Authors & Affiliations

Yoriko Lill1, Wallace A. Kaserer2, Salete M. Newton2, Markus Lill3, Phillip E. Klebba2, and Ken Ritchie1,*

  • 1Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA
  • 2Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA
  • 3Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana 47907, USA

  • *kpritchie@purdue.edu

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Issue

Vol. 86, Iss. 2 — August 2012

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