The ER is the sorting core facility in the Golgi ‐lacking protozoan Giardia lamblia

ABSTRACT Our understanding of protein and lipid trafficking in eukaryotic cells has been challenged by the finding of different forms of compartmentalization and cargo processing in protozoan parasites. Here, we show that, in the absence of a Golgi compartment in Giardia, proteins destined for secretion are directly sorted and packaged at specialized ER regions enriched in COPII coatomer complexes and ceramide. We also demonstrated that ER‐resident proteins are retained at the ER by the action of a KDEL receptor, which, in contrast to other eukaryotic KDEL receptors, showed no interorganellar dynamic but instead acts specifically at the limit of the ER membrane. Our study suggests that the ER‐exit sites and the perinuclear ER‐membranes are capable of performing protein sorting functions. In our view, the description presented here suggests that Giardia adaptation represents an extreme example of reductive evolution without loss of function. Synopsis Regulated protein trafficking in the protozoa Giardia lamblia shows some singularities. (1) After performing its chaperone function, BiP is retained at the ER lumen by the KDELR for further cycles of protein folding. (2) CWP (Cyst Wall Protein) 1–3 are folded and recruited to form the nascent ESVs (Encystation Specific Vesicles). (3) The COPII‐subunits, Sec23 and Sec24, cycle between forming the complex in the ceramide‐enriched ERES membrane to its dissociation after vesicle formation. (4) Nascent ESVs go throug...
Source: Traffic - Category: Research Authors: Tags: ORIGINAL ARTICLE Source Type: research