Estimated upper limit for size of cytoplasmic components that are not affected by metabolism-dependent motion

Range 30 - 40 nm
Organism Bacteria Caulobacter crescentus
Reference Parry BR et al. (2014) The bacterial cytoplasm has glass-like properties and is fluidized by metabolic activity. Cell 156: 183–94. doi: 10.1016/j.cell.2013.11.028. p.187 right column 2nd paragraphPubMed ID24361104
Method (Abstract): "Through single-particle tracking of protein filaments, plasmids, storage granules, and foreign particles of different sizes, [researchers] find that the bacterial cytoplasm displays properties that are characteristic of glass-forming liquids and changes from liquid-like to solid-like in a component size-dependent fashion."
Comments "Of equal interest, the ratio {R[g](untreated)-R[g](+DNP)}/R[g](+DNP) decreased toward 0 as size decreased (Figure 3E), with an estimated intercept near 30–40 nm assuming a linear relationship. This finding suggests that cytoplasmic components smaller than this estimated size are not affected by metabolism-dependent motion...[researchers] show that, above a certain size scale (~30 nm), the bacterial cytoplasm behaves differently from a simple (viscous) fluid. Instead, it displays striking features (such as non-Gaussian distributions of displacements with long tails, nonergodicity, caging, and dynamic heterogeneity Figures 4B, 4E, 5A, and 6) that are characteristic of colloidal glasses (Cipelletti and Ramos, 2005 Hunter and Weeks, 2012)...Based on [researchers'] rough critical size estimation, [they] expect that cytoplasmic constituents =30nm will be subject to metabolism-dependent motion. This implies that proteins, which typically have a size <10 nm, will not be affected, consistent with the minimal effect of DNP on the apparent diffusion of free GFP in C. crescentus (Montero Llopis et al., 2012)." R[g]=radius of gyration. (DNP+)=DNP (2,4-dinitrophenol) treated condition=energy depleted
Entered by Uri M
ID 110499