Thiamine pyrophosphate (TPP family), pyrimidine (PYR) binding domain of pyruvate oxidase (POX) subfamily. The PYR domain is found in many key metabolic enzymes which use TPP (also known as thiamine diphosphate) as a cofactor. TPP binds in the cleft formed by a PYR domain and a PP domain. The PYR domain, binds the aminopyrimidine ring of TPP, the PP domain binds the diphosphate residue. The PYR and PP domains have a common fold, but do not share strong sequence conservation. The PP domain is not included in this sub-family. Most TPP-dependent enzymes have the PYR and PP domains on the same subunit although these domains can be alternatively arranged in the primary structure. TPP-dependent enzymes are multisubunit proteins, the smallest catalytic unit being a dimer-of-active sites. Lactobacillus plantarum POX is a homotetramer (dimer-of-homodimers), having two active sites per homodimer lying between PYR and PP domains of different subunits. POX decarboxylates pyruvate, producing hydrogen peroxide and the energy-storage metabolite acetylphosphate.