Sunday, July 24, 2011

New player in ER-Peroxisome field

Peroxisomes proliferate by growth and division as well as they can arise de novo from Endoplasmic reticulum. In yeast, it was recently shown that most PMPs transit to peroxisomes via ER. In mammalian cells, Pex16 and Pex3 are known to target peroxisomes via ER. But the key players involved in this ER-peroxisome transport are still poorly known.

The new study published in PNAS identifies Sec16B as factor essential for Pex16 export from ER to peroxisomes. 
Yonekawa et al, Online published before print on 18 july 2011, PNAS

Sec16B(Sec16S) is a vertebrate specific isoform which is less extensively studied than the Sec61A(Sec16L). Comparing the sizes, Sec16B is almost half the size that of Sec16A and these proteins are able to form heteromeric complexes too.

This study found that, overexpression of Sec16B results in reduced number of peroxisomes and ER localization of Pex16 and Pex3. On the other hand, siRNA mediated knockdown of Sec16B results in tubulated peroxisomes, ER localization of pex16 and degradation of Pex3 by Ubiquitin proteasomal system. Authors also characterized different regions of Sec16B and found that C-terminal of Sec16B which differs from Sec16A, is required for its function in peroxisome biogenesis. Peroxisome vesicle formation from ER is known to be independent of COPII vesicle budding. Sec16A as well as Sec16B are involved formation of COPII vesicles and are targeted to ERES(ER Exit Sites). Authors meticulously shown that, stretch of Sec16B  responsible for its recruitment to ERES is not required for its peroxisome related function.

Further reading

PNAS, May 2011

PNAS, December 2011

BBA Mol Cell Research, in press

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