A unique leucine-valine adhesive motif supports structure and function of protein disulfide isomerase P5 via dimerization

Abstract

Highlights d P5 dimerizes via a unique leucine-valine adhesive motif in the first Trx-like domain d The adhesive motif is radically different from conventional coiled-coil motifs d The dimeric structure serves to promote P5-mediated inactivation of IRE1a d Ca 2+ -binding regions and Ca 2+ -dependent functional regulation were clarified for P5

Ca2+ Regulates ERp57-Calnexin Complex Formation

“…Therefore, we believe that Ca 2+ -dependent ERp57-CNX complex formation is physiologically relevant and capable of responding to fluctuations in Ca 2+ concentration. In line with this, previous studies demonstrated that the chaperoning functions of PDI and P5 are negatively suppressed by Ca 2+ [10,23], implicating Ca 2+ as a functional regulator of ER-resident chaperones.…”

“…Thermal-induced aggregation of luciferase was observed by monitoring the increase in absorbance at 350 nm (Figure 4). Addition of ERp57 (Figure 4, red) yielded the same rate as spontaneous aggregation (black), suggesting that ERp57 has lower chaperone activity against amorphous aggregation than PDI and P5 [10,29]. Notably, only CNX or ERp57/CNX complex inhibited aggregation even more effectively than ERp57.…”

“…Regarding the client recruiting mechanism, cutting-edge technology in the form of time-resolved single-molecule observations by highspeed atomic force microscopy demonstrated that PDI displays striking redox-dependent conformational dynamics, and consequently assembles to form a face-to-face dimer with a central hydrophobic cavity during the early folding pathway of clients, resulting in an efficient protein folding apparatus with an increased catalytic rate [7]. Unlike the substrate recognition mechanism of PDI, several solvent-exposed redox active sites of ERp46 and P5 are dedicated to rapid but promiscuous disulfide introduction [8][9][10]. Clients with multiple disulfide bonds are likely to have complicated oxidative folding pathways, hence differences in client recognition mechanisms by PDIs might be indispensable for dealing with various conformers and folding states [11].…”

“…In addition to enzymatic functions, several ER-resident proteins including PDI [23], P5 [10], and CNX bind to Ca 2+ [24], which is stored at high concentration (~1 mM) in the ER [25]. The chaperoning functions of PDI and P5 are negatively regulated by Ca 2+ , although the impact of Ca 2+ on ERp57 is still unclear.…”

Functional Interplay between P5 and PDI/ERp72 to Drive Protein Folding

“…Like PDI, P5 (also known as ERp5 or PDIA6) is one of PDIs involved in ER protein quality control that assists oxidative folding [ 13 , 14 , 36 , 37 , 38 ], inhibits protein aggregation [ 36 , 37 ], and regulates the ER stress response [ 16 , 36 , 39 , 40 , 41 ]. P5 consists of three thioredoxin (Trx)-like domains ( Figure 1 a) [ 11 , 16 ] and dimerizes via a unique leucine-valine adhesive motif contained in the N-terminal Trx-like domain [ 36 ]. This motif is involved in the regulation of its chaperone activity and the regulation of intermolecular disulfide bonds in the ER stress sensor IRE1 [ 36 ].…”