Rapid Diffusion of Green Fluorescent Protein in the Mitochondrial Matrix
TL;DR: The rapid and unrestricted diffusion of solutes in the mitochondrial matrix suggests that metabolite channeling may not be required to overcome diffusive barriers, and it is proposed that the clustering of matrix enzymes in membrane-associated complexes might serve to establish a relatively uncrowded aqueous space in which solutes can freely diffuse.
Abstract: It is thought that the high protein density in the mitochondrial matrix results in severely restricted solute diffusion and metabolite channeling from one enzyme to another without free aqueous-phase diffusion. To test this hypothesis, we measured the diffusion of green fluorescent protein (GFP) expressed in the mitochondrial matrix of fibroblast, liver, skeletal muscle, and epithelial cell lines. Spot photobleaching of GFP with a 100x objective (0.8-micron spot diam) gave half-times for fluorescence recovery of 15-19 ms with >90% of the GFP mobile. As predicted for aqueous-phase diffusion in a confined compartment, fluorescence recovery was slowed or abolished by increased laser spot size or bleach time, and by paraformaldehyde fixation. Quantitative analysis of bleach data using a mathematical model of matrix diffusion gave GFP diffusion coefficients of 2-3 x 10(-7) cm2/s, only three to fourfold less than that for GFP diffusion in water. In contrast, little recovery was found for bleaching of GFP in fusion with subunits of the fatty acid beta-oxidation multienzyme complex that are normally present in the matrix. Measurement of the rotation of unconjugated GFP by time-resolved anisotropy gave a rotational correlation time of 23.3 +/- 1 ns, similar to that of 20 ns for GFP rotation in water. A rapid rotational correlation time of 325 ps was also found for a small fluorescent probe (BCECF, approximately 0.5 kD) in the matrix of isolated liver mitochondria. The rapid and unrestricted diffusion of solutes in the mitochondrial matrix suggests that metabolite channeling may not be required to overcome diffusive barriers. We propose that the clustering of matrix enzymes in membrane-associated complexes might serve to establish a relatively uncrowded aqueous space in which solutes can freely diffuse.
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TL;DR: It is demonstrated that transient binding can account for an apparent violation of the GSE relation and it is shown that, for high protein concentrations, the diffusion of small molecules such as dioxane or water is not generally a suitable probe for the viscosity experienced by the diffusing proteins.
Abstract: The effect of high concentration, also referred to as crowding conditions, on Brownian motion is of central relevance for the understanding of the physical, chemical and biological properties of proteins in their native environment. Specifically, the simple inverse relationship between the translational diffusion coefficient and the macroscopic solution viscosity as predicted by the generalized Stokes–Einstein (GSE) relation has been the subject of many studies, yet a consensus on its applicability has not been reached. Here, we use isotope-filtered pulsed-field gradient NMR to separately assess the μm-scale diffusivity of two proteins, BSA and an SH3 domain, in mixtures as well as single-protein solutions, and demonstrate that transient binding can account for an apparent violation of the GSE relation. Whereas GSE behavior applies for the single-protein solutions, it does not hold for the protein mixtures. Transient binding behavior in the concentrated mixtures is evidenced by calorimetric experiments and by a significantly increased apparent activation energy of diffusion. In contrast, the temperature dependence of the viscosity, as well as of the diffusivity in single-component solutions, is always dominated by the flow activation energy of pure water. As a practically relevant second result, we further show that, for high protein concentrations, the diffusion of small molecules such as dioxane or water is not generally a suitable probe for the viscosity experienced by the diffusing proteins.
26 citations
01 Jan 2001
TL;DR: This chapter starts with a general discussion on diffusive particle motion in cells and highlights the controversy that is associated with this topic, and introduces nonlinear microscopy, a very powerful noninvasive technique for examining dynamical processes in living cells.
Abstract: Diffusion of molecular compounds through the intracellular space is an extremely important biophysical process that lies at the heart of cellular functioning. Yet, due to the complexity of the cellular interior, the understanding of molecular diffusion in living cells is far from complete. Experimental interrogation of intracellular molecular motions is hampered by the stringent physiological conditions as imposed by the living cell, the indefinite composition of the sample and the microscopic spatial scale that is characteristic of cellular life. This chapter starts with a general discussion on diffusive particle motion in cells and highlights the controversy that is associated with this topic. We next zoom in on a very powerful noninvasive technique for examining dynamical processes in living cells: optical microscopy. Next to a brief overview of conventional microscopy methods the concept of nonlinear microscopy is introduced. It is emphasized that nonlinear microscopic techniques provide new ways of probing biological samples. As explained in the last part of this introductory chapter, a few of these novel techniques will be put into service to investigate molecular mobility in living cells.
25 citations
TL;DR: Overexpression of the pro-apoptotic protein appoptosin impairs interaction of the mitochondrial fusion proteins MFN1 and MFN2, and reduces mitochondrial fusion activity, leading to mitochondrial fragmentation.
Abstract: Mitochondrial morphology is regulated by fusion and fission machinery. Impaired mitochondria dynamics cause various diseases, including Alzheimer's disease. Appoptosin (encoded by SLC25A38) is a mitochondrial carrier protein that is located in the mitochondrial inner membrane. Appoptosin overexpression causes overproduction of reactive oxygen species (ROS) and caspase-dependent apoptosis, whereas appoptosin downregulation abolishes β-amyloid-induced mitochondrial fragmentation and neuronal death during Alzheimer's disease. Herein, we found that overexpression of appoptosin resulted in mitochondrial fragmentation in a manner independent of its carrier function, ROS production or caspase activation. Although appoptosin did not affect levels of mitochondrial outer-membrane fusion (MFN1 and MFN2), inner-membrane fusion (OPA1) and fission [DRP1 (also known as DNM1L) and FIS1] proteins, appoptosin interacted with MFN1 and MFN2, as well as with the mitochondrial ubiquitin ligase MITOL (also known as MARCH5) but not OPA1, FIS1 or DRP1. Appoptosin overexpression impaired the interaction between MFN1 and MFN2, and mitochondrial fusion. By contrast, co-expression of MFN1, MITOL and a dominant-negative form of DRP1, DRP1(K38A), partially rescued appoptosin-induced mitochondrial fragmentation and apoptosis, whereas co-expression of FIS1 aggravated appoptosin-induced apoptosis. Together, our results demonstrate that appoptosin can interact with mitochondrial outer-membrane fusion proteins and regulates mitochondrial morphology.
25 citations
Cites methods from "Rapid Diffusion of Green Fluorescen..."
...mtGFP and mtRFP were generated by fusing GFP or RFP to mitochondria-localized COX8, following the previously reported procedure (Partikian et al., 1998)....
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...MFN1, MFN2, DRP1, FIS1, MITOL and DRP1K38A plasmids were constructed using pCMV-HA, pCMV-Myc or pEGFP-C1 as backbones. mtGFP and mtRFP were generated by fusing GFP or RFP to mitochondria-localized COX8, following the previously reported procedure (Partikian et al., 1998)....
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TL;DR: In this article, the physicochemical properties of the crowding molecules govern and determine kinetics, equilibria and mechanism of action of biochemical and biological reactions, processes and functions.
25 citations
TL;DR: The results demonstrate that FAST is well-suited for single-molecule localization microscopy (SMLM), and the small size and the availability of spectrally distinct fluorogens present unique advantages of the FAST system as a potential orthogonal labeling strategy.
Abstract: We develop and employ the Fluorescence-Activating and absorption-Shifting Tag (FAST) system for super-resolution (SR) imaging and single-molecule tracking based on single-molecule localizations. The fast off rate of fluorogen binding, combined with its spatially well-separated labeling of the densely expressed FAST fusion proteins, allowed single-molecule measurements to be performed in both living and fixed cells. The well-separated fluorescence localization density was achieved by either reversibly controlling the fluorogen concentration or by irreversibly photobleaching the FAST-fluorogen complex. The experimentally determined resolution of 28 nm allowed us to resolve Ensconsin-labeled microtubules and to track single molecules in mitochondria. Our results demonstrate that FAST is well-suited for single-molecule localization microscopy (SMLM). The small size and the availability of spectrally distinct fluorogens present unique advantages of the FAST system as a potential orthogonal labeling strategy th...
25 citations
References
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TL;DR: The theoretical basis and some practical guidelines for simple, rigorous analysis of FPR experiments are presented and some model experiments on aqueous solutions of rhodamine 6G are described.
2,594 citations
"Rapid Diffusion of Green Fluorescen..." refers background in this paper
...As discussed by Axelrod et al. (1976) for conventional two-dimensional spot photobleaching, this approximation is reasonably valid for practical laser/lens systems; the same considerations would apply for bleaching of long thin mitochondria where bleach profile is nearly constant across the thin…...
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TL;DR: The green fluorescent protein (GFP) from the Pacific Northwest jellyfish Aequorea victoria has generated intense interest as a marker for gene expression and localization of gene products.
Abstract: The green fluorescent protein (GFP) from the Pacific Northwest jellyfish Aequorea victoria has generated intense interest as a marker for gene expression and localization of gene products. The chromophore, resulting from the spontaneous cyclization and oxidation of the sequence -Ser65 (or Thr65)-Tyr66-Gly67-, requires the native protein fold for both formation and fluorescence emission. The structure of Thr65 GFP has been determined at 1.9 angstrom resolution. The protein fold consists of an 11-stranded beta barrel with a coaxial helix, with the chromophore forming from the central helix. Directed mutagenesis of one residue adjacent to the chromophore, Thr203, to Tyr or His results in significantly red-shifted excitation and emission maxima.
2,232 citations
TL;DR: The crystal structure of recombinant wild-type green fluorescent protein (GFP) has been solved to a resolution of 1.9 Å by multiwavelength anomalous dispersion phasing methods and the identification of the dimer contacts may allow mutagenic control of the state of assembly of the protein.
Abstract: The crystal structure of recombinant wild-type green fluorescent protein (GFP) has been solved to a resolution of 1.9 A by multiwavelength anomalous dispersion phasing methods. The protein is in the shape of a cylinder, comprising 11 strands of s-sheet with an α-helix inside and short helical segments on the ends of the cylinder. This motif, with s-structure on the outside and α-helix on the inside, represents a new protein fold, which we have named the s-can. Two protomers pack closely together to form a dimer in the crystal. The fluorophores are protected inside the cylinders, and their structures are consistent with the formation of aromatic systems made up of Tyr86 with reduction of its Cα-Cs bond coupled with cyclization of the neighboring glycine and serine residues. The environment inside the cylinder explains the effects of many existing mutants of GFP and suggests specific side chains that could be modified to change the spectral properties of GFP. Furthermore, the identification of the dimer contacts may allow mutagenic control of the state of assembly of the protein.
1,502 citations
"Rapid Diffusion of Green Fluorescen..." refers background in this paper
...The three–amino acid chromophore in GFP is fixed rigidly within a barrel structure (Yang et al., 1996; Örmo et al., 1996)....
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1,070 citations
TL;DR: This minireview has attempted to provide some overall perspective on the question of how various forms of diffusion in reduced dimensions, or diffusion within a nonspecifically bound state, can speed biological interactions beyond the limits normally set by three-dimensional diffusion processes.
1,017 citations