Structural Motif Descriptors as a Way To Elucidate the Agonistic or Antagonistic Activity of Growth Hormone–Releasing Hormone Peptide Analogues

The synthesis of analogues of hypothalamic neuropeptide growth hormone-releasing hormone (GHRH) is an efficient strategy for designing new therapeutic agents. Several promising synthetic agonist and antagonist analogues of GHRH have been developed based on amino acid mutations of the GHRH (1-29) sequence. Because structural information on the activity of the GHRH agonists or antagonists is limited, there is a need for more effective analytical workflows capable of correlating the peptide sequence with biological activity. In the present work, three GHRH agonists-MR-356, MR-406, and MR-409-and three GHRH antagonists-MIA-602, MIA-606, and MIA-690-were investigated to assess the role of substitutions in the amino acid sequence on structural motifs and receptor binding affinities. The use of high resolution trapped ion mobility spectrometry coupled to mass spectrometry allowed the observation of a large number of peptide-specific mobility bands (or structural motif descriptors) as a function of the amino acid sequence and the starting solution environment. A direct correlation was observed between the amino acid substitutions (i.e., basic residues and d/l-amino acids), the structural motif descriptors, and the biological function (i.e., receptor binding affinities of the GHRH agonists and antagonists). The simplicity, ease, and high throughput of the proposed workflow based on the structural motif descriptors can significantly reduce the cost and time during screening of new synthetic peptide analogues.