This is the dimerisation element domain found in bacterial modular polyketide synthase ketoreductases [1]. The dimerization element (DE) domain is N-terminal to the KR domain Pfam:PF08659. DE domain is necessary for KR function, presumably because the dimeric DE orients the KR domains for optimal activity within a module [2].

1: The missing linker: a dimerization motif located within polyketide synthase modules. Zheng J, Fage CD, Demeler B, Hoffman DW, Keatinge-Clay AT; ACS Chem Biol. 2013;8:1263-1270. PMID:23489133

2: Structural studies of an A2-type modular polyketide synthase ketoreductase reveal features controlling alpha-substituent stereochemistry. Zheng J, Piasecki SK, Keatinge-Clay AT; ACS Chem Biol. 2013;8:1964-1971. PMID:23755878