This is a Plants and Prokaryotes Conserved (PPC) domain found in proteins that contain AT-hook motifs Pfam:PF02178 which strongly suggests a DNA-binding function for the proteins as a whole. Proteins with PPC domains are found in Bacteria, Archaea and the plant kingdom [1, 2].The PPC domain has a single alpha-helix packed against an antiparallel beta-sheet, which is formed by five beta-strands. There are three highly conserved histidine residues, eg at 117, 119 and 133 in Swiss:Q46QL5 which appear to form a zinc-binding site, and the domain has been observed to form homotrimers. The domain co-occurs with a thioredoxin-like domain in uncharacterized cyanobacterial proteins [2].

1: Identification of a novel plant MAR DNA binding protein localized on chromosomal surfaces. Fujimoto S, Matsunaga S, Yonemura M, Uchiyama S, Azuma T, Fukui K; Plant Mol Biol. 2004;56:225-239. PMID:15604740

2: Crystal structure of Pyrococcus horikoshii PPC protein at 1.60 A resolution. Lin L, Nakano H, Nakamura S, Uchiyama S, Fujimoto S, Matsunaga S, Kobayashi Y, Ohkubo T, Fukui K; Proteins. 2007;67:505-507. PMID:17295322