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Tic20 and Tic22 are new components of the protein import apparatus at the chloroplast inner envelope membrane.

Kouranov A, Chen X, Fuks B, Schnell DJ - J. Cell Biol. (1998)

Bottom Line: In contrast, Tic22 is a 22-kD protein that is located in the intermembrane space between the outer and inner envelope membranes and is peripherally associated with the outer face of the inner membrane.Preprotein import intermediates quantitatively associate with this outer/inner membrane supercomplex, providing evidence that the complex corresponds to envelope contact sites that mediate direct transport of preproteins from the cytoplasm to the stromal compartment.On the basis of these results, we propose that Tic20 and Tic22 are core components of the protein translocon of the inner envelope membrane of chloroplasts.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Rutgers, The State University of New Jersey, Newark, New Jersey 07102, USA.

ABSTRACT
Two components of the chloroplast envelope, Tic20 and Tic22, were previously identified as candidates for components of the general protein import machinery by their ability to covalently cross-link to nuclear-encoded preproteins trapped at an intermediate stage in import across the envelope (Kouranov, A., and D.J. Schnell. 1997. J. Cell Biol. 139:1677-1685). We have determined the primary structures of Tic20 and Tic22 and investigated their localization and association within the chloroplast envelope. Tic20 is a 20-kD integral membrane component of the inner envelope membrane. In contrast, Tic22 is a 22-kD protein that is located in the intermembrane space between the outer and inner envelope membranes and is peripherally associated with the outer face of the inner membrane. Tic20, Tic22, and a third inner membrane import component, Tic110, associate with import components of the outer envelope membrane. Preprotein import intermediates quantitatively associate with this outer/inner membrane supercomplex, providing evidence that the complex corresponds to envelope contact sites that mediate direct transport of preproteins from the cytoplasm to the stromal compartment. On the basis of these results, we propose that Tic20 and Tic22 are core components of the protein translocon of the inner envelope membrane of chloroplasts.

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Identification of Tic20 and Tic22 as components of the  inner envelope membrane. Samples (50 μg of protein) from stromal extract (stroma), thylakoid membranes (thylakoids), enriched inner envelope membrane vesicles (IM), and outer envelope membrane vesicles (OM) were resolved by SDS-PAGE,  transfered to nitrocellulose, and then immunoblotted with (A)  anti-Tic20, (B) anti-Tic22, (C) a mixture of anti-Tic20 and anti-Tic22 preimmune sera, or (D) a mixture of anti-Tic110 and anti-Toc75 sera.
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Figure 3: Identification of Tic20 and Tic22 as components of the inner envelope membrane. Samples (50 μg of protein) from stromal extract (stroma), thylakoid membranes (thylakoids), enriched inner envelope membrane vesicles (IM), and outer envelope membrane vesicles (OM) were resolved by SDS-PAGE, transfered to nitrocellulose, and then immunoblotted with (A) anti-Tic20, (B) anti-Tic22, (C) a mixture of anti-Tic20 and anti-Tic22 preimmune sera, or (D) a mixture of anti-Tic110 and anti-Toc75 sera.

Mentions: To define the suborganellar localization of Tic20 and Tic22, chloroplast subfractions enriched in outer membranes, inner membranes, thylakoid membranes, and stroma were resolved by SDS-PAGE and immunoblotted with anti-Tic20 and anti-Tic22 sera. The distribution of Tic20 and Tic22 in chloroplast subfractions (Fig. 3, A and B) is similar to that of the inner membrane protein, Tic110 (Fig. 3 D), but distinct from the outer membrane protein, Toc75 (Fig. 3 D). Both proteins were detected only in fractions containing inner membrane proteins consistent with their association with this membrane (Fig. 3, A and B). The preimmune sera of anti-Tic20 and anti-Tic22 showed no reactivity with proteins in the chloroplast extracts (Fig. 3 C).


Tic20 and Tic22 are new components of the protein import apparatus at the chloroplast inner envelope membrane.

Kouranov A, Chen X, Fuks B, Schnell DJ - J. Cell Biol. (1998)

Identification of Tic20 and Tic22 as components of the  inner envelope membrane. Samples (50 μg of protein) from stromal extract (stroma), thylakoid membranes (thylakoids), enriched inner envelope membrane vesicles (IM), and outer envelope membrane vesicles (OM) were resolved by SDS-PAGE,  transfered to nitrocellulose, and then immunoblotted with (A)  anti-Tic20, (B) anti-Tic22, (C) a mixture of anti-Tic20 and anti-Tic22 preimmune sera, or (D) a mixture of anti-Tic110 and anti-Toc75 sera.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132967&req=5

Figure 3: Identification of Tic20 and Tic22 as components of the inner envelope membrane. Samples (50 μg of protein) from stromal extract (stroma), thylakoid membranes (thylakoids), enriched inner envelope membrane vesicles (IM), and outer envelope membrane vesicles (OM) were resolved by SDS-PAGE, transfered to nitrocellulose, and then immunoblotted with (A) anti-Tic20, (B) anti-Tic22, (C) a mixture of anti-Tic20 and anti-Tic22 preimmune sera, or (D) a mixture of anti-Tic110 and anti-Toc75 sera.
Mentions: To define the suborganellar localization of Tic20 and Tic22, chloroplast subfractions enriched in outer membranes, inner membranes, thylakoid membranes, and stroma were resolved by SDS-PAGE and immunoblotted with anti-Tic20 and anti-Tic22 sera. The distribution of Tic20 and Tic22 in chloroplast subfractions (Fig. 3, A and B) is similar to that of the inner membrane protein, Tic110 (Fig. 3 D), but distinct from the outer membrane protein, Toc75 (Fig. 3 D). Both proteins were detected only in fractions containing inner membrane proteins consistent with their association with this membrane (Fig. 3, A and B). The preimmune sera of anti-Tic20 and anti-Tic22 showed no reactivity with proteins in the chloroplast extracts (Fig. 3 C).

Bottom Line: In contrast, Tic22 is a 22-kD protein that is located in the intermembrane space between the outer and inner envelope membranes and is peripherally associated with the outer face of the inner membrane.Preprotein import intermediates quantitatively associate with this outer/inner membrane supercomplex, providing evidence that the complex corresponds to envelope contact sites that mediate direct transport of preproteins from the cytoplasm to the stromal compartment.On the basis of these results, we propose that Tic20 and Tic22 are core components of the protein translocon of the inner envelope membrane of chloroplasts.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Rutgers, The State University of New Jersey, Newark, New Jersey 07102, USA.

ABSTRACT
Two components of the chloroplast envelope, Tic20 and Tic22, were previously identified as candidates for components of the general protein import machinery by their ability to covalently cross-link to nuclear-encoded preproteins trapped at an intermediate stage in import across the envelope (Kouranov, A., and D.J. Schnell. 1997. J. Cell Biol. 139:1677-1685). We have determined the primary structures of Tic20 and Tic22 and investigated their localization and association within the chloroplast envelope. Tic20 is a 20-kD integral membrane component of the inner envelope membrane. In contrast, Tic22 is a 22-kD protein that is located in the intermembrane space between the outer and inner envelope membranes and is peripherally associated with the outer face of the inner membrane. Tic20, Tic22, and a third inner membrane import component, Tic110, associate with import components of the outer envelope membrane. Preprotein import intermediates quantitatively associate with this outer/inner membrane supercomplex, providing evidence that the complex corresponds to envelope contact sites that mediate direct transport of preproteins from the cytoplasm to the stromal compartment. On the basis of these results, we propose that Tic20 and Tic22 are core components of the protein translocon of the inner envelope membrane of chloroplasts.

Show MeSH
Related in: MedlinePlus