Structure of the Sgt2 dimerization domain complexed with the Get5 UBL domain involved in the targeting of tail-anchored membrane proteins to the endoplasmic reticulum

Abstract

The insertion of tail-anchored membrane (TA) proteins into the appropriate membrane is a post-translational event that requires stabilization of the transmembrane domain and targeting to the proper destination. Sgt2, a small glutamine-rich tetratricopeptide-repeat protein, is a heat-shock protein cognate (HSC) co-chaperone that preferentially binds endoplasmic reticulum-destined TA proteins and directs them to the GET pathway via Get4 and Get5. The N-terminal domain of Sgt2 seems to exert dual functions. It mediates Get5 interaction and allows substrate delivery to Get3. Following the N-terminus of Get5 is a ubiquitin-like (Ubl) domain that interacts with the N-terminus of Sgt2. Here, the crystal structure of the Sgt2 dimerization domain complexed with the Get5 Ubl domain (Sgt2N-Get5Ubl) is reported. This complex reveals an intimate interaction between one Sgt2 dimer and one Get5 monomer. This research further demonstrates that hydrophobic residues from both Sgt2 and Get5 play an important role in cell survival under heat stress. This study provides detailed molecular insights into the specific binding of this GET-pathway complex.

Solution Structure of the SGTA Dimerisation Domain and Investigation of Its Interactions with the Ubiquitin-Like Domains of BAG6 and UBL4A

“…The very recent past saw a number of simultaneous publications from different research groups providing new insights into SGTA, its relationship with the BAG6 holdase complex and the equivalent yeast system including [10], [18], [22], [24], [25]. As a result of the concurrent timing most of these studies did not have the benefit of knowing about each other during their preparation and hence there is some overlap.…”

“…Our group solved the solution structure of the Sgt2 dimerisation domain (Sgt2_NT) which forms a novel helical fold [18]. Various other Sgt2/SGTA structures have also been added to the literature, namely NMR solution [22] and X-ray crystal [25] structures of partial forms of Sgt2_NT in the context of its complex with Get5, and SGTA_NT [22] encompassing the first two or three out of the four helices in each monomer that we present here. These structures largely agree with each other, differing predominantly in the C-terminal regions remote from the UBL binding interface, apparently as a result of the use of truncated constructs of SGTA and Sgt2 in the latter studies.…”

GdX/UBL4A null mice exhibit mild kyphosis and scoliosis accompanied by dysregulation of osteoblastogenesis and chondrogenesis

“…15,16 The BAG6 complex facilitates the ER-associated degradation of certain aberrant membrane proteins and the ubiquitination and degradation of mislocalized membrane and secretory proteins that fail to reach the ER and remain in the cytosol. 17,18 However, it was also showed that GdX interacted with Arp2/3 in membrane ruffles and lamellipodia and eventually influenced insulin-induced Akt plasma membrane translocation. 10 Interestingly, we previously observed GdX associated with STAT3 to mediate its dephosphorylation.…”

Tah1 helix-swap dimerization prevents mixed Hsp90 co-chaperone complexes

“…Furthermore, the TPR domain of Sgt1 (suppressor of G2 allele SKP1, not to be confused with Sgt2 and SgtA) has also been shown to homodimerize, although structural detail of this is also lacking (Nyarko et al, 2007). In contrast, Sgt2 and SgtA (small glutamine-rich TPR-containing protein) have an N-terminal dimerization domain (Tung et al, 2013;Liou & Wang, 2005;Chartron et al, 2012;Tobaben et al, 2003), as does the orthologue from Caenorhabditis elegans (Worrall et al, 2008), for which structural details of the dimerization have recently been reported (Chartron et al, 2012). These differ from those of Tah1 and suggest that many different mechanisms of dimerization may be employed by TPR domain-containing proteins.…”