Katragadda Madan, Magotti Paola, Sfyroera Georgia, Lambris John D
Protein Chemistry Laboratory, Department of Pathology & Laboratory Medicine, School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Med Chem. 2006 Jul 27;49(15):4616-22. doi: 10.1021/jm0603419.
Tryptophans at positions 4 and 7 of compstatin, a peptide complement inhibitor, are crucial for its interaction with C3. However, the nature of their involvement has not been studied to date. Here we investigate the molecular forces involved in the C3-compstatin interactions, mediated by aromatic residues, by incorporating in these two positions various tryptophan analogues (5-methyltryptophan, 5-fluorotryptophan, 1-methyltryptophan, and 2-naphthylalanine) and assessing the resulting peptides for activity by enzyme-linked immunosorbent assay (ELISA) and binding by isothermal titration calorimetry (ITC). Of all the compstatin analogues, peptides containing 1-methyltryptophan at position 4 exhibited the highest binding affinity (Kd = 15 nM) and activity (IC50 = 0.205 microM), followed by a peptide containing 5-fluorotryptophan at position 7. Our observations suggest that hydrophobic interactions involving residues at position 4 and the hydrogen bond initiated by the indole nitrogen are primarily responsible and crucial for the increase in activity. These findings have important implications for the design of clinically useful complement inhibitors.
一种肽补体抑制剂——补体抑制素，其4位和7位的色氨酸对于它与C3的相互作用至关重要。然而，它们所涉及的具体性质至今尚未得到研究。在此，我们通过在这两个位置引入各种色氨酸类似物（5-甲基色氨酸、5-氟色氨酸、1-甲基色氨酸和2-萘丙氨酸），并通过酶联免疫吸附测定（ELISA）评估所得肽的活性以及通过等温滴定量热法（ITC）测定其结合情况，来研究由芳香族残基介导的C3 - 补体抑制素相互作用中涉及的分子力。在所有补体抑制素类似物中，4位含有1-甲基色氨酸的肽表现出最高的结合亲和力（Kd = 15 nM）和活性（IC50 = 0.205 microM），其次是7位含有5-氟色氨酸的肽。我们的观察结果表明，涉及4位残基的疏水相互作用以及由吲哚氮引发的氢键对活性的增加起主要作用且至关重要。这些发现对于设计临床上有用的补体抑制剂具有重要意义。
