Vesicular tubular clusters between the ER and Golgi mediate concentration of soluble secretory proteins by exclusion from COPI-coated vesicles.
We have determined the concentrations of the secretory proteins amylase and chymotrypsinogen and the membrane proteins KDELr and rBet1 in COPII- and COPI-coated pre-Golgi compartments of pancreatic cells by quantitative immunoelectron microscopy. COPII was confined to ER membrane buds and adjacent vesicles. COPI occurred on vesicular tubular clusters (VTCs), Golgi cisternae, the trans-Golgi network, and immature secretory granules. Both secretory proteins exhibited a first, significant concentration step in noncoated segments of VTC tubules and were excluded from COPI-coated tips. By contrast, KDELr and rBet1 showed a first, significant concentration in COPII-coated ER buds and vesicles and were prominently present in COPI-coated tips of VTC tubules. These data suggest an important role of VTCs in soluble cargo concentration by exclusion from COPI-coated domains.
Department of Cell Biology, University Medical Center and Institute of Biomembranes, Utrecht University, The Netherlands.
J A
JA
Martínez-Menárguez
H J
HJ
Geuze
J W
JW
Slot
J
J
Klumperman
D000681:Amylases / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D002919:Chymotrypsinogen / Q000378:metabolism*; D003034:Coated Pits, Cell-Membrane / Q000378:metabolism* / Q000648:ultrastructure; D020756:Coatomer Protein; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D010179:Pancreas / Q000502:physiology* / Q000648:ultrastructure; D010750:Phosphoproteins / Q000378:metabolism; D050767:Qc-SNARE Proteins; D051381:Rats; D017208:Rats, Wistar; D018000:Receptors, Peptide / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins
C098783:BET1 protein, rat; D002352:Carrier Proteins; D020756:Coatomer Protein; C064459:KDEL receptor; D008565:Membrane Proteins; D010750:Phosphoproteins; D050767:Qc-SNARE Proteins; D018000:Receptors, Peptide; C106113:SEC31 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D002919:Chymotrypsinogen; D000681:Amylases