This entry represents a putative redox-active protein of about 140 residues, with four perfectly conserved Cys residues. It includes a CGAXXG motif. Most members are found within one or two loci of transporter or oxidoreductase genes. A member from Geobacter sulfurreducens, located in a molybdenum transporter operon, has a TAT (twin-arginine translocation) signal sequence for Sec-independent transport across the plasma membrane, a hallmark of bound prosthetic groups such as FeS clusters.