由鈣依賴性抗生素衍生之硼依賴性抗生素

Abstract

抗生素抗藥性對公共衛生構成的威脅日益嚴重。為應對這一挑戰，開發新型抗生素勢在必行。鈣離子依賴性抗生素(Calcium-dependent antibiotic, CDA)是一類非核糖體合成的環狀脂肽。因其獨特的作用機制，使它們在未來的抗生藥物開發上受期待。CDA 藉由與鈣離子結合引發構型變化，從而抑制革蘭氏陽性菌生長，其生物活性高度依賴鈣離子的存在。然而，在人體內環境中，鈣離子的濃度不足以活化大部分的CDA。 在我們先前的研究中，合成了Laspartomycin C (LspC) 的衍生物，其環外第1 個與在環內的第7個胺基酸皆被替換成絲胺酸(serine, Ser)。此衍生物可被苯硼酸(phenylboronic acid, PBA)活化，不再須要鈣離子，使其轉變為一種硼依賴性抗生素(boron-dependent antibiotic, BDA)。在本研究中，我們將相同的Ser取代策略延伸至其他CDA，以評估PBA 是否同樣能活化它們的抗菌潛力。 我們挑選了三種CDA: 達托黴素(Daptomycin, DAP)、弗留利黴素Friulimicin B (FruB) 與CDAx。它們在結構上皆與LspC存在特定差異。我們利用固相胜肽合成法合成了Ser取代的衍生物與其對應的原始序列胜肽衍生物作為對照組，並以最低抑菌濃度試驗來評估其抗菌活性。 研究結果顯示，CDAx的 Ser 取代衍生物可被 PBA 活化，進而抑制細菌的生長；相對地，修改後的 FruB與DAP衍生物則未表現出可偵測的活性。這些結果揭示了將 CDA 轉化為BDA的 Ser 替換策略不具有普遍適用性。這種差異化的反應表明，儘管所有 CDA 皆透過鈣離子依賴性活化，但它們在CDA家族中的機制細節和結構要求存在異質性。

The rise of antibiotic resistance poses a growing threat to public health. To respond to this challenge, new antimicrobial agents are needed. Calcium-dependent antibiotics (CDA) are a class of non-ribosomally synthesized cyclic lipopeptides. CDAs inhibit Gram-positive bacteria by undergoing a conformational change upon binding calcium ion(s) (Ca(II)). Due to their unique mechanism of action, CDAs have shown potential as candidates for future antibiotic development. However, a major limitation to their clinical application is that the Ca(II) concentration in the human physiological environment is often insufficient to fully activate most CDA members. In our previous study, we synthesized a LspC analogue, in which the first exocyclic and the seventh amino acids in the macrocycle were replaced with serine (Ser). This engineered derivative, unlike its native counterpart, could be activated by phenylboronic acid (PBA) and no longer required Ca(II), effectively transforming it into a boron-dependent antibiotic (BDA). In this work, we applied the same Ser-substitution strategy to three other structurally diverse CDAs: daptomycin (DAP), friulimicin B (FruB), and CDAx. Peptides were synthesized using solid-phase peptide synthesis, and their antibacterial activity was evaluated through minimum inhibitory concentration assays. Our results showed that only the Ser-substituted CDAx analogue exhibited PBA-dependent activation, while the Ser-analogues of FruB and DAP were inactive. These findings suggest that the Ser-substitution strategy to create BDAs from CDAs is not a generalizable strategy. This differential response indicates that despite sharing Ca(II)-dependent activation, the mechanistic details and structural requirements across the CDA family are likely different.