Conformational analysis of cyclo(2,9)-Ac-QCRSVEGSCG-OH from the C-terminal loop of human growth hormone (original) (raw)
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Conformational analysis of human growth hormone [6-13] peptide analogues
International Journal of Peptide and Protein Research, 1996
The conformational analysis of a series of ten hGH[6-131 peptide analogues is reported. As part of our earlier studies, the r-aminosuccinimide modified fragment Asu1'-hGH[6-l 31 has previously been identified as a potentiator of insulin activity in intravenous insulin tolerance tests, and various analogues have been subsequently designed, synthesised and employed to acquire structure-activity data. These studies have lead to the conclusion that the conformational characteristics at the C-terminus of each of the active peptide analogues is important to the biological activity. In the present investigation, molecular dynamics and simulated annealing techniques have been used to examine the accessible conformational states of the C-terminal region of ten different hGH[6-13] peptide analogues. Of these six are active peptide analogues while the other four show no biological activity. Examination of the conformer groups identified using this molecular dynamics approach showed a common conformational motif for each of the active peptides. Q Munksgaard 1996.
Intra-molecular Conformational Stability in Human Growth Hormone
Journal of Nepal Physical Society, 2020
Human growth hormone (hGH) is synthesized, stored and secreted by somatotropic cells within the lateral wings of the anterior lobe of pituitary glands; and is transported to other organs of human body. Study of intra-molecular structure and its binding mechanisms within the molecule gives more insight of structural stability of the molecule and is also essential in drug designing. In this article, we have investigated the various bonded and non-bonded interactions that contribute for the conformation of entire structure of the hGH molecule using molecular dynamics (MD) simulation. The MD outcomes show that the molecule is hydrophobic in nature. In its conformation, several types of interactions exist, such as disulphide bridges (bonded) and nonbonded: hydrogen bond, hydrophobic, aromatic-aromatic, ionic, aromatic-sulphur, cation-pi.
Journal of Molecular Biology, 2002
N NMR relaxation parameters and amide 1 H/ 2 H-exchange rates have been used to characterize the structural flexibility of human growth hormone (rhGH) at neutral and acidic pH. Our results show that the rigidity of the molecule is strongly affected by the solution conditions. At pH 7.0 the backbone dynamics parameters of rhGH are uniform along the polypeptide chain and their values are similar to those of other folded proteins. In contrast, at pH 2.7 the overall backbone flexibility increases substantially compared to neutral pH and the average order parameter approaches the lower limit expected for a folded protein. However, a significant variation of the backbone dynamics through the molecule indicates that under acidic conditions the mobility of the residues becomes more dependent on their location within the secondary structure units. In particular, the order parameters of certain loop regions decrease dramatically and become comparable to those found in unfolded proteins. Furthermore, the HN-exchange rates at low pH reveal that the residues most protected from exchange are clustered at one end of the helical bundle, forming a stable nucleus. We suggest that this nucleus maintains the overall fold of the protein under destabilizing conditions. We therefore conclude that the acid state of rhGH consists of a structurally conserved, but dynamically more flexible helical core surrounded by an aura of highly mobile, unstructured loops. However, in spite of its prominent flexibility the acid state of rhGH cannot be considered a "molten globule" state because of its high stability. It appears from our work that under certain conditions, a protein can tolerate a considerable increase in flexibility of its backbone, along with an increased penetration of water into its core, while still maintaining a stable folded conformation.
Biochemistry, 1994
In this study we have demonstrated that the C-terminus of helix 1 of porcine G H (pGH) is a receptor-interactive region, thus extending the current binding site model of GH. This was achieved by introducing charge reversal mutations into this region of pGH, which influenced receptor affinity and Ca2+ dependence of binding. The first mutant (R34E pGH, conversion of Arg 34 to Glu) introduced a putative Ca2+ binding site which is present in human G H (hGH) [Barnard et al. (1989) J. Theor. Biol. 140, and sits opposite E220 of receptor subunit 1. This mutant exhibited increased Ca2+ dependence of receptor binding but even at optimal Ca2+ did not display higher than wild-type affinity. Introduction of a second Ca2+ binding site adjacent to the first by a second charge reversal (K30E R34E pGH) further increased Ca2+ dependence of binding and also increased affinity for the rabbit G H receptor (2.4 f 0.4)-fold relative to wild-type pGH at optimal Ca2+. Equilibrium dialysis and Scatchard analysis of binding of 45Ca2+ to pGH and K30E R34E pGH revealed two Ca2+ binding sites on wild-type pGH and an additional two Ca2+ binding sites on the K30E R34E pGH mutant ( K d 0.5-0.8 mM), as predicted. A third partial charge reversal mutant in the fourth helix (H170D) also led to enhanced Ca2+ dependence of binding, supporting our proposal that E34 and D170 are responsible for the Ca2+ dependence of hGH binding to the rabbit G H receptor. Examination of the crystal structure shows that E34 and D170 are in close proximity and would interact repulsively with a cluster of acidic residues on the receptor consisting of E126, E127, and E220 unless neutralized by Ca2+ or an introduced basic residue. Accordingly, charge reversal at the adjacent pGH residue E33 (E33K pGH) led to a Ca2+ independent (3.0 f 0.4)-fold increase in affinity of binding. As well as extending the binding site model of GH, these studies provide a mechanistic explanation for the unique Ca2+ dependence of hGH binding to the rabbit G H receptor. They also indicate that charge reversal can be used to design higher affinity G H analogues and could assist in the mapping of interactive regions in ligand-receptor complexes generally.
The Molecular Properties of Human Growth Hormone
Journal of Biological Chemistry, 1972
The stability of human growth hormone to acid, alkali, and urea has been evaluated by fluorescence, absorption, and circular dichroism spectroscopy. In accord with previous studies on other growth hormones and prolactins, similar molecular transitions were observed although small shifts in parameters were found among the different proteins. It is of interest to find such a resemblance in properties between human growth hormone and ovine prolactin since the number of residues occupying identical positions is less than 20% and the longest identical sequ.ence is a tripeptide. It is clear from recent studies on the amino acid sequences of the growth aud lactogenic hormones of several animal species (human, bovine, and ovine) that they have arisen from a common ancestor by gene duplication (1-11). The growth and lactogenic hormoues have numerous molecular properties in common (size, shape, helical content, solubility) which presumably result from their sequence homology (12m-19). Although there are major differences in their hormonal potencies there is some overlap in both hormonal and biochemical activities (20-24). Consequently, either structural or sequence differences are responsible for the important differences in biological response. There is extensive sequence homology among HGH', BGH, and HCS but only limited homology between these hormones and ovine prolactin (9, 11). It is of interest to compare the effects of these variations in their sequences on the structural parameters of these proteins. Since their '%tatic" properties resemble each other rather closely, it is more useful to look at their behavior under stress, i.e. conditions which tend to produce configurational modifications. The resistance to molecular transitions should be a function of all the interactions which constrain the protein to its native structure. Consequently, various transitions of HGH have been evaluat,ed under conditions which are known to affect the structure of the other hormones. Changes in secondary structure can be ascertained from the circular dichroic activity of the peptide bond (25) whereas those
Chemical Biology & Drug Design, 2010
Incorporation of amino lactams into biologically active peptides restricts conformational mobility and may enhance selectivity and increase potency. a-and b-amino c-lactams (Agl and Bgl), in both S and R configurations, were introduced into the growth hormone secretagogue GHRP-6 using a Fmoc-compatible solid-phase protocol relying on N-alkylation with five-and six-membered cyclic sulfamidates, followed by lactam annulation under microwave heating. Using this protocol in conjunction with IRORI Kan TM techniques furnished eleven new GHRP-6 analogs, and their binding affinity IC 50 values on both the growth hormone secretagogue receptor 1a (GHS-R1a) and CD36 receptors are herein reported. The results indicate that selectivity towards one receptor or the other can be modulated by lactam substitution, typically at the Ala 3 and the D-Phe 5 positions.