Probable 3-methyl-2-oxobutanoate hydroxymethyltransferase required for pantothenic acid biosynthesis (PubMed:11154694). Acts downstream in the pantothenic acid pathway (PubMed:11154694). (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + 3-methyl-2-oxobutanoate + H2O = (6S)-5,6,7,8-tetrahydrofolate + 2-dehydropantoate Cofactor biosynthesis; (R)-pantothenate biosynthesis; (R)-pantoate from 3-methyl-2-oxobutanoate: step 1/2. Impairs growth on beta-alanine but can still utilize pantothenic acid. Present with 1420 molecules/cell in log phase SD medium. Belongs to the PanB family.