The biological potency of a series of analogues of human calcitonin correlates with their interactions with phospholipids

Abstract

The conformational and lipid binding properties of several calcitonin analogs were compared. These analogs were designed to have the central amphipathic helical region of salmon calcitonin and N- and C-terminal segments similar to human calcitonin. The various analogs differed from one another either by removal of Leu19 from this hybrid analog, replacement of Leu19 with Gly19 or having a carboxyl terminus more closely related to salmon calcitonin. It had been found that replacement of Leu19 with Gly19 caused a marked reduction in the hypocalemic activity of the analog. The ability of the analogs to form helical structures in the presence of dimyristoylphosphatidylglycerol as well as their ability to lower the enthalpy of the calorimetric phase transition of this phospholipid correlates well with the hypocalcemic potency of the peptide.

Structural Determinants of Salmon Calcitonin Bioactivity

“…We first studied the solution conformation, the receptor binding affinity, and the hypocalcemic potency for Leu 23 ,Ala 24 -sCT (mutant 19), which was expected to take up a helix longer than sCT. Our results indicated that sCT and Leu 23 ,Ala 24 -sCT both form an amphiphatic ␣-helix, but whereas in Leu 23 ,Ala 24 -sCT it covers almost the whole sequence (Leu 4 -Gly 28 ), in the native hormone a shorter region (Thr 6 -Phe 22 ) is involved, with the region Leu 9 -Leu 19 constantly found in helical conformation (12). Significantly, no helix-tail interaction was observed for Leu 23 ,Ala 24 -sCT.…”

“…The ␣-helical central region of CT peptides has been reported to interact directly with the receptor N terminus (20), and a short segment of the hCTRa close to the transmembrane domain 1 is proximal to amino acid 19 of helix (21). Furthermore, a strict relationship between the binding receptor affinity and the helicity of the hormone has been observed, with a correlation between amphipathicity and potency (16,22).…”

Chemical modification of Class II G protein-coupled receptor ligands: Frontiers in the development of peptide analogs as neuroendocrine pharmacological therapies

“…Thus, combining the ideal helix of salmon calcitonin with the remainder of the human peptide has the potential to produce an analog with more biological potency than the native human hormone. Several analogs have been manufactured using the amphipathic helical region of the salmon calcitonin and the carboxyl and amino termini of the human calcitonin (Epand et al, 2004). It has been shown that by replacing leucine with glycine at position 19 within the peptide, which creates a carboxyl terminus more similar to salmon calcitonin, there is significantly reduced hypocalcemic activity.…”

“…C) N-terminal modification of GLP-1-(1-18) at Ala 2 produces the analog [D-Ala 2 ]GLP-1-(1-18) (Xiao et al, 2001). D) Chimera formation of the CT derivative sCT-(9-23)-hCT-(1-8, 24-31) occurs by joining segments of hCT and sCT (Epand et al, 2004). …”

“…Abbreviations used: GLP-1, glucagon-like peptide-1; mPEG, mono-poly(ethylene glycol); GIP, glucose-dependent insulinotropic polypeptide; I-SA, 131 I radioactively-labeled, tyrosine-substituted secretin analog; Mpr14-rADM, mercaptoproprionic acid (14) -substituted analog of rat adrenomedullin; dAla 2 , D-alanine (2) ; sCT, salmon calcitonin; hCT, human calcitonin; Pro-pro-hPTH (1-34) , proline-proline-human parathyroid hormone (1-34) . Subscripted numbers in parentheses indicate the positions of amino acid residues of interest within the native peptide. a Feinglos et al, 2005 b Lee et al, 2005 c Gault et al, 2008 d Banks et al, 2002 e Champion et al, 1996 f Xiao et al, 2001 g Epand et al, 2004 h Chunxiao et al, 2007 …”