Activates the five peptidyl carrier protein (PCP) domains of gramicidin synthase GrsAB, by transferring the 4'-phosphopantetheinyl moiety of coenzyme A (CoA) to a serine residue. Required for gramicidin S production. apo-[peptidyl-carrier protein] + CoA = adenosine 3',5'-bisphosphate + H(+) + holo-[peptidyl-carrier protein] Belongs to the P-Pant transferase superfamily. Gsp/Sfp/HetI/AcpT family.