Fig. 5.

The chaperone activity of TXNL1 does not require its Cys residues. When Trx1-driven insulin reduction was performed in the presence of TXNL1 variants with or without its Cys residues mutated, the reduced insulin did not precipitate at any appreciable rate (upper part of the figure, red, blue and green absorbance traces; cf. Trx1-only trace in Fig. 3). If Trx1 was omitted from the reaction, no NADPH consumption was seen with the active site mutant (orange) or completely Cys-less variant (brown) that were identical with a control containing all components, except a Trx-fold protein (grey). All reaction mixtures contained 300 μM NADPH, 10 nM TrxR1, and TXNL1 variants or Trx1 each applied at 10 μM concentration. The lower part of the figure shows a photo of the corresponding microtiter plate wells after completion of the assay, illustrating a slight turbidity in the wells containing the Cys-mutated TXNL1 variants together with Trx1. See text for further details. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)