This is the C-terminal rubredoxin metal binding domain found in Interest in lipopolysaccharide (LPS) assembly protein B (LapB) . Rubredoxin proteins form small non-heme iron binding sites that use four cysteine residues to coordinate a single metal ion in a tetrahedral environment. Rubredoxins are most commonly found in bacterial systems, but have also been found in eukaryotes. The key features of these rubredoxin-like domains are the extended loops or 'knuckles' and the tetracysteine mode of iron binding. Structural analysis of LapB from Escherichia coli show that the rubredoxin metal binding domain is intimately bound to the TPR motifs and that this association to the TPR motifs is essential to LPS regulation and growth in vivo [1]. Other family members include RadA proteins which play a role in DNA damage repair. In E. coli, a protein known as RadA (or Sms) participates in the recombinational repair of radiation-damaged DNA in a process that uses an undamaged DNA strand in one DNA duplex to fill a DNA strand gap in a homologous sister DNA duplex. RadA carries a zinc finger at the N-terminal domain [2].

1: An Unexpected Duo: Rubredoxin Binds Nine TPR Motifs to Form LapB, an Essential Regulator of Lipopolysaccharide Synthesis. Prince C, Jia Z; Structure. 2015;23:1500-1506. PMID:26190574

2: Fine Epitope Mapping of Monoclonal Antibodies to the DNA Repair Protein, RadA. Stuart MK, Hudman DA, Nachtrab SN, Hiatt JL, Seo J, Pullen SJ, Sargentini NJ; Monoclon Antib Immunodiagn Immunother. 2017;36:83-94. PMID:28581365