Structural and physiologic characterization of the mid-region secretory species of parathyroid hormone-related protein

Parathyroid hormone-related protein (PTHrP) is initially translated as a preprohormone which is posttranslationally processed to yield a family of mature secretory forms. Most attention has focused on the amino-terminal portion of the molecule which is homologous to parathyroid hormone. It is clear, however, that a mid-region species of PTHrP is posttranslationally cleaved from the highly conserved mid-region of PTHrP, and that the amine terminus of this peptide is Ala³⁸. The purposes of the current study were three: 1) to confirm that Arg³⁷ immediately preceding Ala³⁸ serves as a posttranslational processing site in the PTHrP precursor, 2) to determine the carboxyl terminus of the mid-region secretory species of PTHrP, and 3) to synthesize this authentic mid-region secretory form of PTHrP and determine whether it is biologically active. The results indicate that: 1) Arg³⁷ is indeed a processing site in the PTHrP precursor; 2) three distinct mid- region PTHrP species are generated by posttranslational processing, PTHrP(38- 94)amide, PTHrP(38-95), and most likely, PTHrP(38-101); and 3) synthetic mid- region PTHrP(3894)amide is active in four different biological systems. These studies confirm the finding that PTHrP is a prohormone. More importantly, they define a novel, biologically active highly conserved mid-region secretory form of PTHrP.