Bi-directional trafficking in the early protein secretary protein pathway is a universal phenomenon within eukaryotic cells. In yeast, the retrograde trafficking based on COPI coated vesicles from Golgi back to ER has essential functions in recycling vesicle components and retrieving escaped ER resident proteins. This retrograde trafficking involves several steps, in which some mechanisms and molecules are still elusive. In previous researches, v-SNARE Sec22p was found mislocalized into vacuole in sec26^PNEE mutant strain. And the Sec26p is one subunit of COPI coatomer complex, which demonstrates a possible interaction between Sec22p and coatomer complex. Also considering the sorting Sec22p into COPI is still elusive, the coatomer complex is suspected to be sorting receptor f...[ Read more ]

Bi-directional trafficking in the early protein secretary protein pathway is a universal phenomenon within eukaryotic cells. In yeast, the retrograde trafficking based on COPI coated vesicles from Golgi back to ER has essential functions in recycling vesicle components and retrieving escaped ER resident proteins. This retrograde trafficking involves several steps, in which some mechanisms and molecules are still elusive. In previous researches, v-SNARE Sec22p was found mislocalized into vacuole in sec26^PNEE mutant strain. And the Sec26p is one subunit of COPI coatomer complex, which demonstrates a possible interaction between Sec22p and coatomer complex. Also considering the sorting Sec22p into COPI is still elusive, the coatomer complex is suspected to be sorting receptor for Sec22p. However, the SNAREs have little binding affinity to coatomer in bio-chemical experiments. So some other molecules might function as sorting receptors, linking Sec22p and coatomer. On the other hand, our lab’s previous researches found that sly1^T81I is synthetic lethal with sec26^PNEE, indicating the possible link between Sly1p and coatomer. SLY1 belongs to the SM protein family, cycling between ER and Golgi and is involved in bi-directional trafficking and able to bind to free SNAREs such as Sed5p and Bet1p. So a hypothetical model is offered that Sly1p may function as a linker for Sec22p and/or other SNAREs and coatomer. The potential role of Sly1p in interaction between Sec22p and coatomer is the major target to look for. In my study, Sly1p is found to bind to Sec22p in vitro and reduced binding between Sly1p and sec22p mutants that are mislocalized into vacuole is found.

Overexpression of Sly1p in vivo seems like to have specific effect in shifting Sec22p to ER while no effect to those sec22p mutants. On the other hand, Sly1p might bind to only two subunits of coatomer: Ret1p and Ret2p, rather than the whole coatomer complex in vitro. The interaction between Sly1p and the two subunits of coatomer cannot be affected by pre-treating Sly1p with t-SNARE Sed5p. So the hypothetical binding model is modified into that Sly1p might function as linker for binding to Sec22p and two subunits of coatomer, which may involves other elusive mechanisms.