Catalyzes the decarboxylation of the cysteine moiety of 4-phosphopantothenoylcysteine to form 4'-phosphopantotheine and this reaction forms part of the biosynthesis of coenzyme A. H(+) + N-[(R)-4-phosphopantothenoyl]-L-cysteine = (R)-4'-phosphopantetheine + CO2 Binds 1 FMN per subunit. Cofactor biosynthesis; coenzyme A biosynthesis; CoA from (R)-pantothenate: step 3/5. Homotrimer. The Met-1 codon is associated with a polymorphism (dbSNP:rs2304899) that replaces the initiation ATG codon by an ATA codon. Belongs to the HFCD (homooligomeric flavin containing Cys decarboxylase) superfamily.