Unconventional protein secretion of Helja, an apoptotic lectin

Abstract

Proteins following unconventional protein secretion (UPS) bypass the RE-Golgi system to reach theapoplast. They use vesicular and no vesicular routes for their transport. Vesicular UPS can encompassdifferent pathways not fully characterized. In these work we analyze the route of Helja secretion, asunflower lectin lacking signal peptide but immunodetected extracellularly. Transient expression ofrecombinant Green fluorescent Helja (GFP-Helja) in Nicotiana Benthamiana leaves allow its apoplasticobservation verified by partial co-localization (Pearson r Value= 0.65) with the specific marker sec-RFP.Florescent intracellular punctate and mobile structures were also visualized. They did not co-localizewith the Golgi marker Sialyltransferase -RFP and their distribution was not affected by Brefeldin A, theinhibitor of RE-Golgi transport.Additionally, GFP-Helja neither co-localize with the multivesicular bodies marker Rha-RFP nor with theendocytic marker FM4-64. Our results support the UPS secretion of HELJA to the apoplast by a yetunidentified vesicular pathway.