‘Come into the fold’: A comparative analysis of bacterial redox enzyme maturation protein members of the NarJ subfamily

Redox enzyme maturation proteins (REMPs) are system-specific chaperones required for the maturation of complex iron sulfur molybdoenzymes that are important for anaerobic respiration in bacteria. Although they perform similar biological roles, REMPs are strikingly different in terms of sequence, structure, systems biology, and type of terminal electron acceptor that it supports for growth. Here we critically dissect current knowledge pertaining to REMPs of the nitrate reductase delta superfamily, specifically recognized in Escherichia coli to include NarJ, NarW, TorD, DmsD, and YcdY, also referred to as the NarJ REMP subfamily. We show that NarJ subfamily members share sequence homology and similar structural features as revealed by alignments performed on structurally characterized REMPs. We include an updated phylogenetic analysis of subfamily members, justifying their classification in this subfamily. The structural and functional roles of each member are presented herein and these discussions suggest that although NarJ subfamily members are related in sequence and structure, each member demonstrates remarkable uniqueness, validating the concept of system-specific chaperones.