This is helix turn helix domain found in polyketide synthases (PKSs) in fungi. They are multidomain enzymes that biosynthesize a wide range of natural products. Family members include citrinin polyketide synthases which contain a C-methyltransferase (CMeT) domain Pfam:PF08242 that adds one or more S-adenosylmethionine (SAM)-derived methyl groups to the carbon framework [1].

1: Functional and Structural Analysis of Programmed C-Methylation in the Biosynthesis of the Fungal Polyketide Citrinin. Storm PA, Herbst DA, Maier T, Townsend CA; Cell Chem Biol. 2017;24:316-325. PMID:28238725

2: Domain Organization and Active Site Architecture of a Polyketide Synthase C-methyltransferase. Skiba MA, Sikkema AP, Fiers WD, Gerwick WH, Sherman DH, Aldrich CC, Smith JL; ACS Chem Biol. 2016;11:3319-3327. PMID:27723289

3: Biosynthesis of t-Butyl in Apratoxin A: Functional Analysis and Architecture of a PKS Loading Module. Skiba MA, Sikkema AP, Moss NA, Lowell AN, Su M, Sturgis RM, Gerwick L, Gerwick WH, Sherman DH, Smith JL; ACS Chem Biol. 2018;13:1640-1650. PMID:29701944