The golgin coiled-coil proteins of the Golgi apparatus

Abstract

A number of long coiled-coil proteins are present on the Golgi. Often referred to as "golgins," they are well conserved in evolution and at least five are likely to have been present in the last common ancestor of all eukaryotes. Individual golgins are found in different parts of the Golgi stack, and they are typically anchored to the membrane at their carboxyl termini by a transmembrane domain or by binding a small GTPase. They appear to have roles in membrane traffic and Golgi structure, but their precise function is in most cases unclear. Many have binding sites for Rab family GTPases along their length, and this has led to the suggestion that the golgins act collectively to form a tentacular matrix that surrounds the Golgi to capture Rab-coated membranes in the vicinity of the stack. Such a collective role might explain the lack of cell lethality seen following loss of some of the genes in human familial conditions or mouse models.

Figure 1.

The golgin coiled-coil proteins of humans. Schematic representations of known human golgins. Regions predicted to form coiled-coils are shown in gray, and known domains involved in protein function or subcellular targeting are indicated.

Figure 2.

A speculative model for golgin function. The golgins surround the Golgi in an array of loosely associated tentacles. Golgin-specific interactions anchor the proteins via their carboxyl termini to particular parts of the Golgi, but the different golgins share at least some binding partners. This allows cytosolic proteins such as kinases or cytoskeletal interactors to bind to as much of the Golgi stack as is required. Transport vesicles or adjacent cisternae that display activated Rab G proteins are captured by binding directly to Rab binding motifs shared between subsets of golgins. In addition to the Rabs, other vesicle-associated proteins could also contribute to golgin recognition (Nakamura et al. 1997; Jing et al. 2010; Sohda et al. 2010). If the affinity or Rab specificity of these interactions varied through the stack it might direct vesicle movement from sites with a broad distribution (yellow) to those that are restricted to a particular part of the stack (green).