Targeting bacteria via iminoboronate chemistry of amine-presenting lipids

Abstract

Synthetic molecules that target specific lipids serve as powerful tools for understanding membrane biology and may also enable new applications in biotechnology and medicine. For example, selective recognition of bacterial lipids may give rise to novel antibiotics, as well as diagnostic methods for bacterial infection. Currently known lipid-binding molecules primarily rely on noncovalent interactions to achieve lipid selectivity. Here we show that targeted recognition of lipids can be realized by selectively modifying the lipid of interest via covalent bond formation. Specifically, we report an unnatural amino acid that preferentially labels amine-presenting lipids via iminoboronate formation under physiological conditions. By targeting phosphatidylethanolamine and lysylphosphatidylglycerol, the two lipids enriched on bacterial cell surfaces, the iminoboronate chemistry allows potent labeling of Gram-positive bacteria even in presence of 10% serum, while bypassing mammalian cells and Gram-negative bacteria. The covalent strategy for lipid recognition should be extendable to other important membrane lipids.

Iminoboronate-Based Peptide Cyclization That Responds to pH, Oxidation, and Small Molecule Modulators

“…Recent publications from several groups including our own have shown that intermolecular iminoboronate formation is rapidly reversible under physiologic conditions with dissociation constants in the low mM range. 18–22 We postulated that intramolecular iminoboronate formation should allow spontaneous and highly efficient cyclization of peptides. Importantly, cyclic peptides with iminoboronate linkages should be able to linearize in response to physiologic stimuli, therefore allowing facile control of their functions.…”

“…Similarly, no cyclization was observed when an AB1 residue was placed adjacent to a lysine in peptide sequences. 22 Finally, the negative control peptide P11 (Fig. S15, SI), which presents a deborylated residue (AB4, Fig.…”

Iminoboronate Formation Leads to Fast and Reversible Conjugation Chemistry of α‐Nucleophiles at Neutral pH

“…We [3] and others [4] have shown that, in comparison to simple imines, [5] iminoboronates display much improved thermodynamic stability and allows labeling of biological amines at low millimolar concentrations (Scheme 1a, b). In this contribution, we extend our investigation of the iminoboronate chemistry to α-nucleophiles (Scheme 1c).…”

“…The binding affinity of 2-APBA to acethydrazide was assessed by using UV-vis (Figure S2) and 1 H-NMR spectroscopy (Figure 1b), which yielded comparable dissociation constants in the sub-millimolar range ( K d : ~0.6 mM). In comparison to primary amines, which typically conjugate with 2-APBA at low millimolar concentrations, [3] acethydrazide displays a higher propensity for conjugation with 2-APBA. Similar behavior was observed for benzhydrazide, for which a K d value of 0.5 mM was obtained (Figure S3).…”

“…The synthesis of AB1 was recently reported by our group in the application of iminoboronate chemistry for bacterial imaging. [3] A short peptide CGAB1 with the sequence of Ac-C*G(AB1)-NH 2 was synthesized, where C* denotes a cysteine labeled with Alexa Fluor 488 (AF488, Figure 2a). The conjugation reactions, with 0.2 µM peptide and Phzn over a range of concentrations, were analyzed by using LC-MS. With 1 µM Phzn, CGAB1 was over 90% labeled (Figure S6), demonstrating the high propensity of 2-APBA to conjugate with Phzn to form hydrazones.…”