The thioredoxin-like and one glutaredoxin domain are required to rescue the iron-starvation phenotype of HeLa GLRX3 knock out cells.

Glutaredoxin 3 (Grx3) is a multidomain protein (Trx-GrxA-GrxB) with a Trx-like domain and two Grx domains containing a CGFS motif for binding Fe2S2 clusters. To study the function of these domains, HeLa cells with GLRX3 knockout were generated via CRISPR/Cas. The knockout activated iron-regulatory protein 1, indicating iron starvation due to impaired iron metabolism. Transfection with constructs encoding wild-type or individual domains showed that only the Trx-GrxA construct could rescue the phenotype, matching the effect of full-length Grx3. The specific role of the second Grx domain in human Grx3, absent in simpler eukaryotes such as yeast, remains unclear. While the individual domains are insufficient to rescue the knockout of full-length Grx3, the Trx-GrxA module is functionally critical. Impact statement Glutaredoxin 3 (Grx3) contains a Trx-like domain and two Grx domains. The importance of the domains in higher eukaryotes has not previously been addressed in physiological or cellular contexts. Here, we report GLRX3 knockout results in activation of iron regulatory protein 1, and a Trx-GrxA construct could rescue the phenotype.