Jois S D, Tibbetts S A, Chan M A, Benedict S H, Siahaan T J
Department of Pharmaceutical Chemistry, The University of Kansas, Lawrence 66047, USA.
J Pept Res. 1999 Jan;53(1):18-29. doi: 10.1111/j.1399-3011.1999.tb01613.x.
The objective of this work is to study the conformation of cyclic peptide (1), cyclo (1, 12) Pen1-Gly2-Val3-Asp4-Val5-Asp6-Gln7-+ ++Asp8-Gly9-Glu10-Thr11-Cys12, in the presence and absence of calcium. Cyclic peptide 1 is derived from the divalent cation binding sequence of the alpha-subunit of LFA-1. This peptide has been shown to inhibit ICAM-1-LFA-1 mediated T-cell adhesion. In order to understand the structural requirements for this biologically active peptide, its solution structure was studied by nuclear magnetic resonance (NMR), circular dichroism (CD) and molecular dynamics simulations. This cyclic peptide exhibits two types of possible conformations in solution. Structure I is a loop-turn-loop type of structure, which is suitable to bind cations such as EF hand proteins. Structure II is a more extended structure with beta-hairpin bend at Asp4-Val5-Asp6-Gln7. There is evidence that alterations in the conformation of LFA-1 upon binding to divalent cations cause LFA-1 to bind to ICAM-1. To understand this mechanism, the cation-binding properties of the peptide were studied by CD and NMR. CD studies indicated that the peptide binds to calcium and forms a 1 : 1 (peptide: calcium) complex at low calcium concentrations and multiple types of complexes at higher cation concentrations. NMR studies indicated that the conformation of the peptide is not significantly altered upon binding to calcium. The peptide can inhibit T-cell adhesion by directly binding to ICAM-1 or by disrupting the interaction of the alpha and beta-subunits of LFA-1 protein. This study will help us to understand the mechanism(s) of action of this peptide and will improve our ability to design a better inhibitor of T-cell adhesion.
这项工作的目的是研究环肽（1），即环（1,12）Pen1-Gly2-Val3-Asp4-Val5-Asp6-Gln7-+++Asp8-Gly9-Glu10-Thr11-Cys12，在有钙和无钙情况下的构象。环肽1源自LFA-1α亚基的二价阳离子结合序列。已证明该肽可抑制ICAM-1-LFA-1介导的T细胞黏附。为了了解这种生物活性肽的结构要求，通过核磁共振（NMR）、圆二色性（CD）和分子动力学模拟研究了其溶液结构。这种环肽在溶液中呈现两种可能的构象。结构I是一种环-转角-环类型的结构，适合结合诸如EF手型蛋白的阳离子。结构II是一种更伸展的结构，在Asp4-Val5-Asp6-Gln处有β-发夹弯。有证据表明，LFA-1与二价阳离子结合后构象的改变会导致LFA-1与ICAM-1结合。为了理解这一机制，通过CD和NMR研究了该肽的阳离子结合特性。CD研究表明，该肽在低钙浓度下与钙结合形成1:1（肽:钙）复合物，在较高阳离子浓度下形成多种类型的复合物。NMR研究表明，该肽与钙结合后构象没有明显改变。该肽可通过直接结合ICAM-1或破坏LFA-1蛋白α和β亚基之间的相互作用来抑制T细胞黏附。这项研究将有助于我们理解该肽的作用机制，并提高我们设计更好的T细胞黏附抑制剂的能力。
