Protein sorting in the Golgi complex - PubMed (original) (raw)

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Protein sorting in the Golgi complex

J Füllekrug et al. Biochim Biophys Acta. 1998.

Abstract

Even after one hundred years, the Golgi apparatus remains a major challenge in the field of Cell Biology. This is particularly true in terms of transport and of protein sorting. For example, the question how cargo proteins are transported through this organelle is still a matter of debate. Emphasis has been put on the role of anterograde and retrograde transport vesicles. These have been proposed to carry cargo from cisterna to cisterna and to recycle components needed for further rounds of transport. Alternatively, anterograde movement of cargo takes place in cisternal membranes rather than transport vesicles. These membranes assemble and mature in a cis to trans direction. In this case, retrograde transport vesicles need to recycle all components of the Golgi apparatus and this demands a highly dynamic and efficient sorting machinery. Here we will discuss possible mechanisms for protein sorting in the context of cisternal maturation and propose that a common mechanism is sufficient to explain both transport of cargo and sorting of resident proteins.

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Figures

Fig. 1

Fig. 1

How cisternal maturation would work. Importantly, this drawing depicts not spatial but time resolution. A given population of cargo molecules moves over time t0–t5 through the secretory pathway. t0: Cargo is selected and concentrated at ER exit sites with the help of COP II components. t1: COP II vesicles shed their coat and fuse with retrograde COP I vesicles carrying cis Golgi proteins, forming the first cisterna of the Golgi apparatus. t2: Cargo is modified by cis Golgi proteins, and these enzymes are recycling to fuse with COP II vesicles; at the same time, retrograde vesicles containing medial Golgi enzymes start to join the cargo containing cisterna. t3: Cargo is modified by medial Golgi proteins, and these enzymes are recycling to fuse with cis Golgi cisternae; at the same time, retrograde vesicles containing trans Golgi enzymes start to join the cargo containing cisterna. t4: Cargo is modified by trans Golgi enzymes, and these enzymes are recycling to fuse with medial cisternae; sorting and budding of vesicles result ultimately in the consumption of the trans cisterna. t5: Vesicles move to lysosomes, secretory granules or the plasma membrane. The grey bars at the cytosolic face of the individual cisternae correspond to the intracisternal matrix. If cargo molecules have a certain affinity for retrograde vesicles, they would undergo more than one round of maturation thus explaining different kinetics for transport from ER to plasma membrane. An essential feature of this maturation model is the prediction that Golgi resident proteins are more concentrated in retrograde vesicles than they are in the cisternae of the Golgi apparatus. Furthermore, since new cisternae are only assembled at the ER-Golgi intermediate compartment, every cisterna has to move forward to provide space for newly forming cisternae.

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