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. 2013 Apr 16;8(4):e61596.
doi: 10.1371/journal.pone.0061596. Print 2013.

The asymmetrical structure of Golgi apparatus membranes revealed by in situ atomic force microscope

Haijiao Xu  1 , Weiheng Su, Mingjun Cai, Junguang Jiang, Xianlu Zeng, Hongda Wang
Affiliations

The asymmetrical structure of Golgi apparatus membranes revealed by in situ atomic force microscope

Haijiao Xu et al. PLoS One. .

Abstract

The Golgi apparatus has attracted intense attentions due to its fascinating morphology and vital role as the pivot of cellular secretory pathway since its discovery. However, its complex structure at the molecular level remains elusive due to limited approaches. In this study, the structure of Golgi apparatus, including the Golgi stack, cisternal structure, relevant tubules and vesicles, were directly visualized by high-resolution atomic force microscope. We imaged both sides of Golgi apparatus membranes and revealed that the outer leaflet of Golgi membranes is relatively smooth while the inner membrane leaflet is rough and covered by dense proteins. With the treatment of methyl-β-cyclodextrin and Triton X-100, we confirmed the existence of lipid rafts in Golgi apparatus membrane, which are mostly in the size of 20 nm -200 nm and appear irregular in shape. Our results may be of significance to reveal the structure-function relationship of the Golgi complex and pave the way for visualizing the endomembrane system in mammalian cells at the molecular level.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. AFM images of Golgi apparatus.
(A) AFM image of a stack of membranous cisternae. Scale bar is 1 µm. (B) Magnification of the green square area in (A). (C) Cross-section analysis along the green line drawn in (B). (D) AFM image of tubule network of Golgi apparatus. Scale bar is 1 µm. (E) Magnification of the green square area in (D). (F) Cross-section analysis along the green line drawn in (E). (G) AFM image of vesicles of Golgi apparatus. Scale bar is 1 µm. (H) Magnification of the green square area in (G). (I) Cross-section analysis along the green line drawn in (H).
Figure 2
Figure 2. AFM image of individual Golgi cisternae.
(A) AFM Image of a globular membranous cisterna. Scale bar is 400 nm. (B) Magnification of the cisterna in (A). Scale bar is 200 nm. (C) Higher magnification of the blue boxed area in (B). Scale bar is 100 nm. (D, E, F) Cross section analysis along the green line drawn in (A) (B) and (C). (G) AFM image of a flat membranous cisterna. Blue arrows point to protein particles underneath the cisterna. Scale bar is 500 nm. (H) AFM image of an oval-shaped membranous cisterna with peripheral vesicles. Scale bar is 500 nm. (I and J) Cross section analysis along the green line drawn in images (G) and (H). Green arrows in Fig. 2 point to buds or interconnected vesicles around the cisterna.
Figure 3
Figure 3. AFM image of the inner leaflet of Golgi membrane.
(A) Image of an opened cisterna. Blue and green arrows point to the inner and outer leaflet membranes, respectively. Scale bar is 500 nm. (B) Magnification of the inner membrane leaflet membrane in (A). Scale bar is 100 nm. (C) The inner membrane leaflet of the Golgi cisterna membrane. Scale bar is 500 nm. (D–F) Cross-section analysis along the lines in images (A–C), respectively. (G) Height distribution of proteins in the inner leaflet membrane in (A). (H) Width distribution of proteins in the inner membrane leaflet in (B). (I) Width distribution of proteins in the inner leaflet membrane in (C).
Figure 4
Figure 4. Real-time images of Golgi membrane treated with MβCD.
(A,B,E,F) Series of images after the treatment with MβCD for 0 min (A), 3 min (B), 14 min (E), 22 min (F). Blue arrows in (F) point to the regions of the Golgi membrane eroded by MβCD. Cross-section analyses of images (A, B, E, F) are shown in (C, D, G, H), respectively. (I) Size distribution of the regions of the Golgi membrane eroded by MβCD in Fig. 4F. Scale bar in (A) is 200 nm.
Figure 5
Figure 5. Real-time images of the Golgi inner leaflet membrane treated by Triton X-100.
The images show the different stage after the addition of Triton X-100 for 0 min (A), 15 min (B), 20 min (E), and 48 min (F). Blue arrows in (A) point to the free lipid bilayer. Cross-section analysis along the green lines in images (A, B, E, F) are shown in (C, D, G, H), respectively. (I, J) Height and size distribution of the DRMs in the inner membrane obtained by Triton X-100 treatment. Scale bar in (A) is 200 nm.
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