Volkman B F, Wemmer D E
Department of Chemistry, University of California, Berkeley, California, USA.
Biopolymers. 1997 Apr 5;41(4):451-60. doi: 10.1002/(SICI)1097-0282(19970405)41:4<451::AID-BIP9>3.0.CO;2-L.
The solution conformations of a hybrid sequence peptide related to the bee venom peptide apamin have been determined using two-dimensional 1H-nmr. Apamin is an 18 amino acid peptide containing a C-terminal helix that is stabilized by two disulfide bonds. The deletion of one residue (K4) of the N-terminal "scaffold" region of the apamin sequence results in a helical peptide, but with a change in the pairing of cysteines to form the disulfide cross links. The new disulfide arrangement is analogous to that of the vasoconstrictor peptide endothelin. Two sets of nmr resonances were observed for the apamin-deletion (AD) peptide, due to cistrans isomerism at the A4-P5 peptide bond. The cis isomer of the AD peptide contains a tight turn in residues 3-6, which is required for formation of the alpha-helix in residues 7-15. Nuclear Overhauser effects observed for the trans AD peptide are not consistent with any single unique fold, indicating the presence of conformational averaging when the peptide adopts the trans form. Distance geometry calculations on the cis AD peptide reveal an alpha-helical structure that appears to be more like that of apamin than the crystal structure of human endothelin, despite the reversal of the disulfide pattern in the AD peptide from that of apamin to that of endothelin.
利用二维¹H-核磁共振技术确定了一种与蜂毒肽蜂毒明肽相关的杂合序列肽的溶液构象。蜂毒明肽是一种由18个氨基酸组成的肽，含有一个由两个二硫键稳定的C端螺旋。蜂毒明肽序列N端“支架”区域的一个残基（K4）缺失后会产生一种螺旋肽，但形成二硫交联的半胱氨酸配对发生了变化。新的二硫键排列与血管收缩肽内皮素的类似。由于A4-P5肽键处的顺反异构现象，观察到蜂毒明肽缺失（AD）肽有两组核磁共振共振信号。AD肽的顺式异构体在残基3-6处含有一个紧密转角，这是残基7-15中α-螺旋形成所必需的。观察到的反式AD肽的核Overhauser效应与任何单一独特构象均不一致，表明该肽采用反式构象时存在构象平均化现象。对顺式AD肽进行的距离几何计算揭示了一种α-螺旋结构，尽管AD肽中二硫键模式从蜂毒明肽的模式转变为内皮素的模式，但该结构似乎比人内皮素的晶体结构更类似于蜂毒明肽的结构。
