The structure of GDF9 protein. GDF9 protein model (A) Red, helix; cyan, sheet; gray, coil. Components of the GDF9 protein (B) Red, signal peptide; gray, propeptide; green, mature GDF9. Natural variations of GDF9 (C). Protein processing by glycosylation, disulfide bonds, and post-translational modification by creatine kinase phosphorylation as shown in Golgi (D).