Monday, May 3, 2010

Unconventional protein secretion

               Soluble proteins destined for secretion contain N-terminal or internal signal peptide and they enter co- or post translationally into ER lumen, ultimately travelling trough golgi to plasma membrane. Interestingly many proteins like Fibroblast growth factor 2 (FCF-2), cytokine IL-1β are secreted independent of ER-golgi route. There are many pathways by which this feat can be achieved. The recently discovered pathway for secretion of Acb1 is surprising since it involves peroxisomal components.
                Two articles in JCB shed light upon unconventional secretion of protein Acb1 (acyl CoA-binding protein). First article by Duran et al. explores the participation of autophagosome mediated exocytosis whereas second article by Manjithaya et al. establishes the critical role of peroxisomal components in this process.
                Pex11 is essential for transport of MCFA to peroxisomes. Faa2 is a PTS1 containing acyl-CoA synthetase which is transported to peroxisomal matrix by PTS1 receptor Pex5. Faa2 couples CoA to MCFA to generate MCFA-CoA. Acb1 MCFA-CoA complex travels to plasma membrane through autophagosomes bypassing the vacuoles. The authors also observed that peroxisomal fatty acid β-oxidation as well as PTS2 import pathway is not involved in Acb1 secretion
                This discovery of novel route of secretion is also discussed in Research Highlight in April 2010 issue of Nature Reviews Molecular Cell Biology. Link

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