The pearl jubilee of microcin J25: thirty years of research on an exceptional lasso peptide

Covering: 1992 up to 2023Since their discovery, lasso peptides went from peculiarities to be recognized as a major family of ribosomally synthesized and post-translationally modified peptide (RiPP) natural products that were shown to be spread throughout the bacterial kingdom. Microcin J25 was first described in 1992, making it one of the earliest known lasso peptides. No other lasso peptide has since then been studied to such an extent as microcin J25, yet, previous review articles merely skimmed over all the research done on this exceptional lasso peptide. Therefore, to commemorate the 30th anniversary of its first report, we give a comprehensive overview of all literature related to microcin J25. This review article spans the early work towards the discovery of microcin J25, its biosynthetic gene cluster, and the elucidation of its three-dimensional, threaded lasso structure. Furthermore, the current knowledge about the biosynthesis of microcin J25 and lasso peptides in general is summarized and a detailed overview is given on the biological activities associated with microcin J25, including means of self-immunity, uptake into target bacteria, inhibition of the Gram-negative RNA polymerase, and the effects of microcin J25 on mitochondria. The in vitro and in vivo models used to study the potential utility of microcin J25 in a (veterinary) medicine context are discussed and the efforts that went into employing the microcin J25 scaffold in bioengineering contexts are summed up.

Combined thermal and carboxypeptidase Y stability assays for probing the threaded fold of lasso peptides

Lasso peptides are natural products belonging to the superfamily of ribosomally synthesized and post-translationally modified peptides (RiPPs). The defining characteristic of lasso peptides is their threaded structure, which is reminiscent of a lariat knot. When working with lasso peptides, it is therefore of major importance to understand and evidence their threaded folds. While the full elucidation of their three-dimensional structures via NMR spectroscopy or crystallization remains the gold standard, these methods are time-consuming, require large quantities of highly pure lasso peptides, and therefore might not always be applicable. Instead, the unique properties of lasso peptides in context of their behavior at elevated temperatures and toward carboxypeptidase Y treatment can be leveraged as a tool to investigate and evidence the threaded lasso fold using only minute amounts of compound that does not need to be purified first. This chapter will provide insights into the thermal stability properties of lasso peptides and their behavior when treated with carboxypeptidase Y in comparison to a branched-cyclic peptide with the same amino acid sequence. Furthermore, it will be described in detail how to set up a combined thermal and carboxypeptidase Y stability assay and how to analyze its outcomes.

Exploring structural signatures of the lanthipeptide prochlorosin 2.8 using tandem mass spectrometry and trapped ion mobility-mass spectrometry

Lanthipeptides are a family of ribosomally synthesized and post-translationally modified peptides (RiPPs) characterized by intramolecular thioether cross-links formed between a dehydrated serine/threonine (dSer/dThr) and a cysteine residue. Prochlorosin 2.8 (Pcn2.8) is a class II lanthipeptide that exhibits a non-overlapping thioether ring pattern, for which no biological activity has been reported yet. The variant Pcn2.8[16RGD] has been shown to bind tightly to the αvβ3 integrin receptor. In the present work, tandem mass spectrometry, using collision-induced dissociation (CID) and electron capture dissociation (ECD), and trapped ion mobility spectrometry-mass spectrometry (TIMS-MS) were used to investigate structural signatures for the non-overlapping thioether ring pattern of Pcn2.8. CID experiments on Pcn2.8 yielded b_i and y_j fragments between the thioether cross-links, evidencing the presence of a non-overlapping thioether ring pattern. ECD experiments of Pcn2.8 showed a significant increase of hydrogen migration events near the residues involved in the thioether rings with a more pronounced effect at the dehydrated residues as compared to the cysteine residues. The high-resolution mobility analysis, aided by site-directed mutagenesis ([P8A], [P11A], [P12A], [P8A/P11A], [P8A/P12A], [P11A/P12A], and [P8A/P11A/P12A] variants), demonstrated that Pcn2.8 adopts cis/trans-conformations at Pro8, Pro11, and Pro12 residues. These observations were complementary to recent NMR findings, for which only the Pro8 residue was evidenced to adopt cis/trans-orientations. This study highlights the analytical power of the TIMS-MS/MS workflow for the structural characterization of lanthipeptides and could be a useful tool in our understanding of the biologically important structural elements that drive the thioether cyclization process.

Exploring the Conformational Landscape of a Lanthipeptide Synthetase Using Native Mass Spectrometry

Lanthipeptides are ribosomally synthesized and post-translationally modified peptide (RiPP) natural products. These genetically encoded peptides are biosynthesized by multifunctional enzymes (lanthipeptide synthetases) that possess relaxed substrate specificity and catalyze iterative rounds of post-translational modification. Recent evidence has suggested that some lanthipeptide synthetases are structurally dynamic enzymes that are allosterically activated by precursor peptide binding and that conformational sampling of the enzyme-peptide complex may play an important role in defining the efficiency and sequence of biosynthetic events. These "biophysical" processes, while critical for defining the activity and function of the synthetase, remain very challenging to study with existing methodologies. Herein, we show that native mass spectrometry coupled to ion mobility (native IM-MS) provides a powerful and sensitive means for investigating the conformational landscapes and intermolecular interactions of lanthipeptide synthetases. Namely, we demonstrate that the class II lanthipeptide synthetase (HalM2) and its noncovalent complex with the cognate HalA2 precursor peptide can be delivered into the gas phase in a manner that preserves native structures and intermolecular enzyme-peptide contacts. Moreover, gas phase ion mobility studies of the natively folded ions demonstrate that peptide binding and mutations to dynamic structural elements of HalM2 alter the conformational landscape of the enzyme. Cumulatively, these data support previous claims that lanthipeptide synthetases are structurally dynamic enzymes that undergo functionally relevant conformational changes in response to precursor peptide binding. This work establishes native IM-MS as a versatile approach for characterizing intermolecular interactions and for unraveling the relationships between protein structure and biochemical function in RiPP biosynthetic systems.

Potential allergenicity assessment after bovine apo-α-lactalbumin binding to calcium ion

Bovine α-lactalbumin (α-LA) is recognized as a major milk allergen. Generally, α-LA in the natural state combines with a calcium ion, however, some studies have shown that calcium ions can binding the other metal binding sites in α-LA as well. In our study, the optimal condition of calcium ion binding to α-LA and the change of structure and allergenicity were explored. By optimizing the conditions, the maximum calcium binding amounts of apo-α-LA were obtained in a ratio of 1:4. The structure of α-LA after removal of calcium obviously changed by the spectroscopic detection. For the digestive stability, there was no obvious change in three forms of α-LA. While the allergenic properties were characterized by IgG/IgE inhibition ELISA and the human basophil KU812 degranulation assay. The results showed that IgG and IgE binding decreased, and the degranulation capacity of basophils weakened. Based on these results, calcium binding to apo-α-LA can reduce the potential allergenic properties. PRACTICAL APPLICATIONS: By optimizing the conditions, bovine apo-α-LA can obtain the most calcium binding amount. And calcium binding to apo-α-LA can reduce the potential allergenic properties. Compared with α-LA in the natural state, calcium binding to α-LA not only can reduce the allergenic properties, but also play a role in calcium supplementation. It might be used to guide the development of hypoallergenic α-LA and provide a method to reduce the potential allergenic properties of α-LA.

Evidence of Cis/Trans-Isomerization at Pro7/Pro16 in the Lasso Peptide Microcin J25

Microcin J25 is a ribosomal synthesized and post-translationally modified peptide (RiPP) characterized by a mechanically interlocked topology called the lasso fold. This structure provides microcin J25 a potent antimicrobial activity resulting from internalization via the siderophore receptor FhuA and further inhibition of the RNA polymerase. In the present work, nuclear magnetic resonance (NMR) and trapped ion mobility spectrometry-mass spectrometry (TIMS-MS) were used to investigate the lasso structure of microcin J25. NMR experiments showed that the lasso peptide microcin J25 can adopt conformational states where Pro16 can be found in the cis- and trans-orientations. The high-resolution mobility analysis, aided by site-directed mutagenesis ([P7A], [P16A], and [P7A/P16A] variants), demonstrated that microcin J25 can adopt cis/cis-, cis/trans-, trans/cis-, and trans/trans-conformations at the Pro7 and Pro16 peptide bonds. It was also shown that interconversion between the conformers can occur as a function of the starting solvent conditions and ion heating (collision-induced activation, CIA) despite the lasso topology. Complementary to NMR findings, the cis-conformations at Pro7 were assigned using TIMS-MS. This study highlights the analytical power of TIMS-MS and site-directed mutagenesis for the study of biological systems with large micro-heterogeneity as a way to further increase our understanding of the receptor-binding dynamics and biological activity.