Protein-lysine myristoyltransferase that catalyzes myristoylation of the protoxin (RtxA) at two internal lysine residues, thereby converting it to the active toxin. L-lysyl-[protein] + tetradecanoyl-[ACP] = H(+) + holo-[ACP] + N(6)-tetradecanoyl-L-lysyl-[protein] Belongs to the RTX toxin acyltransferase family.