Binding of SGTA to Rpn13 selectively modulates protein quality control

Leznicki, Pawel; Korac-Prlic, Jelena; Kliza, Katarzyna; Husnjak, Koraljka; Nyathi, Yvonne; Dikic, Ivan; High, Stephen

The capacity of both SGTA and the Bag6 subunit of the heterotrimeric BAG6 complex to bind hydrophobic polypeptides (Hessa et al., 2011; Leznicki et al., 2013, 2011; Minami et al., 2010; Wunderley et al., 2014; Xu et al., 2012), and the proteasome (this study; Kikukawa et al., 2005), raised the possibility that these components modulate the fate of MLPs at the proteasome. To address this question, SGTA and Bag6 were transiently overexpressed in HEK293Rpn11-HTBH cells together with OP91, an N-terminal fragment of the polytopic membrane protein opsin that acts as an MLP (Wunderley et al., 2014). SGTA co-expression led to a marked increase in steady-state OP91 in both HEK293Rpn11-HTBH cells (Fig. 3A, OP91 panel, cf. lanes 4 and 6) and the parental line (supplementary material Fig. S2A), consistent with previous studies (Leznicki and High, 2012; Wunderley et al., 2014). Interestingly, overexpression of the Bag6 protein had a similar effect on the level of OP91 (Fig. 3A, OP91 panel, lanes 4 and 5), in agreement with the previously reported dominant-negative effect exogenous Bag6 expression has on the degradation of aberrant membrane proteins (Payapilly and High, 2014).