Ryu K S, Choi B S, Chi S W, Kim S H, Kim H
Department of Biological Sciences, Korea Advanced Institute of Science and Technology, Taejon, South Korea.
J Biochem. 2000 Apr;127(4):687-94. doi: 10.1093/oxfordjournals.jbchem.a022658.
The corticotropin-releasing factor (CRF) is a 41-amino acid peptide-amide hormone, which mediates a general stress-response. It has been reported that the substitution of His-32 in the ovine CRF (oCRF) with Ala brings about a 4.5-fold increase in activity [Kornreich et al. (1992) J. Med. Chem. 35, 1870-76]. Here, we have determined the secondary structure of this Ala-substituted ovine CRF ([Ala32]oCRF) and compare it with that of oCRF using circular dichroism (CD) and NMR techniques in trifluoroethanol (TFE) solution, which is known to stabilize the alpha-helix formation. In contrast to an earlier report, it was observed the alpha-helical structure extends to the C-terminus of oCRF. By analyzing the CalphaH and NH chemical shifts, the properties of local structures of oCRF were elucidated. The oCRF and [Ala32]oCRF have stable alpha-helical structures in the middle region, regardless of pH and temperature, and the alpha-helix initiation regions of these peptides are stabilized as the pH is decreased. However, the [Ala32]oCRF has a more stable alpha-helical structure than oCRF in the vicinity of the substitution region, and it is thought that this is the cause of the increased activity of [Ala32]oCRF.
促肾上腺皮质激素释放因子（CRF）是一种由41个氨基酸组成的肽酰胺激素，介导一般应激反应。据报道，用丙氨酸替代绵羊CRF（oCRF）中的组氨酸-32会使活性提高4.5倍[科恩赖希等人（1992年）《药物化学杂志》35卷，1870 - 1876页]。在此，我们测定了这种丙氨酸取代的绵羊CRF（[Ala32]oCRF）的二级结构，并在已知能稳定α螺旋形成的三氟乙醇（TFE）溶液中，使用圆二色性（CD）和核磁共振（NMR）技术将其与oCRF的二级结构进行比较。与早期报告不同的是，观察到oCRF的α螺旋结构延伸至C末端。通过分析α碳原子的氢（CαH）和氮氢（NH）化学位移，阐明了oCRF局部结构的性质。无论pH值和温度如何，oCRF和[Ala32]oCRF在中间区域都具有稳定的α螺旋结构，并且随着pH值降低，这些肽的α螺旋起始区域会更加稳定。然而，在取代区域附近，[Ala32]oCRF比oCRF具有更稳定的α螺旋结构，据认为这就是[Ala32]oCRF活性增加的原因。
