Reversible interruption of Giardia lamblia cyst wall protein transport in a novel regulated secretory pathway

To survive in the environment and infect a new host, Giardia lamblia secretes an extracellular cyst wall using a poorly understood pathway. The two cyst wall proteins (CWPs) form disulphide‐bonded heterodimers and are exported via novel encystation‐specific secretory vesicles (ESVs). Exposure of eukaryotic cells to dithiothreitol (DTT) blocks the formation of disulphide bonds in nascent proteins that accumulate in the endoplasmic reticulum (ER) and induces an unfolded protein response (UPR). Proteins that have exited the ER are not susceptible. Exposure to DTT inhibits ESV formation by > 85%. Addition of DTT to encysting cells causes rapid (t1/2