Systematic Structure-Activity Analysis of Microcin J25

Abstract

Microcins are a class of small (Ͻ10 kDa) ribosomally synthesized peptide antibiotics produced by Enterobacteriaceae (1). Some microcins undergo dramatic post-translational modifications by dedicated maturation machinery (2). Post-translationally modified microcins have unusual structures and target important cellular enzymes. The object of this study, microcin J25 (MccJ25), 3 is a 21-amino acid peptide that inhibits the activity of Gram-negative bacterial RNA polymerase (RNAP) and that inhibits growth of Gram-negative bacteria (primarily or exclusively Gram-negative enterics) (3, 4). MccJ25 has an unusual lariat-protoknot ("threaded lasso") structure, consisting of an eight-amino acid cycle with backbone-side chain lactam bond between the ␣-amino group of Gly 1 and the ␥-carboxyl group of Glu 8 , followed by a 13-amino acid tail that loops back and threads through the cycle (5-7). The threaded tail is trapped within the cycle by the aromatic side chains of MccJ25 residues Phe 19 and Tyr 20 , which straddle the cycle (5-8). The unusual lariat-protoknot structure of MccJ25 results in exceptionally high thermal stability and exceptionally high resistance to denaturation by chaotropes and organic solvents (4,8).MccJ25 is produced by bacteria containing a plasmid-borne mcjABCD biosynthetic gene cluster (9). Mature MccJ25 is produced from a 58-amino acid ribosomally synthesized precursor, McjA, the product of the mcjA gene (9). Amino acid residues that become part of Mutations that confer resistance to MccJ25 in nonproducing cells map to the rpoB and rpoC genes (12, 13), which encode the RNAP ␤ and ␤Ј subunits, respectively. RNAP purified from such rpoB or rpoC mutant cells is resistant to MccJ25 in vitro, establishing that RNAP is the functional cellular target of the drug (12). Amino acid substitutions in RNAP that lead to MccJ25 resistance involve residues located in the RNAP secondary channel, which mediates entry of transcription substrates, NTPs, to the RNAP active center. It has been proposed that MccJ25 inhibits transcription, at least in part, by binding within and obstructing the RNAP secondary channel, interfering with entry of . This proposal has received support from biochemical, kinetic, and single-molecule analyses as well as from structural modeling (13,14).The fact that MccJ25 is produced from a ribosomally synthesized precursor enables one to exploit the power of genetic engineering in order to produce a library of MccJ25 mutants that can be screened for desired biological properties. Here, we report the results of such an effort. We present an essentially complete collection of point mutations in the MccJ25 coding portion of the mcjA gene, and we determine the effects of amino acid substitutions resulting from these point mutations on production of MccJ25 (comprising synthesis of MccJ25 precursor, processing of MccJ25 precursor, export of mature MccJ25, and * This work was supported, in whole or in part, by National Institutes of Health Grants GM41376 (to R. H. E.) and GM64530 (to K. S.) and by a NI...

Dual substrate‐controlled kinase activity leads to polyphosphorylated lasso peptides

“…3A), in agreement with previous assays of ThcoK with PadeA (13-23) [34]. When ThcoK was incubated with ATP and either PadeA (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) or deletion variant S-PadeA(13-23) DD22, only a singly phosphorylated peptide was significantly produced (Fig. 3B).…”

“…Plasmids were transformed into E. coli BL21(DE3) cells for expression and subsequent purification of Trx fusion proteins, followed by cleavage with TEV protease and further purification as described above for S-ThcoA and S-SyanA. PadeA (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23) and PadeA(13-23)-PO 2À 3 were purchased from Biomatik (Cambridge, Ontario, Canada) (> 95% purity).…”

“…3A, ThcoK transferred up to three phosphate groups onto S-ThcoA (12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22) when ATP served as the phosphate donor; however, a singly phosphorylated peptide appeared as the main product. Conversely, when ATP was replaced with GTP, singly and doubly phosphorylated peptides were produced in nearly equal amounts.…”

“…Lasso peptides are members of an intriguing family of RiPPs that possess an unusual lariat knot-like structure [6][7][8][9][10][11][12][13][14]: the N terminus of the peptide is covalently cyclized with an acidic side chain to form a 7-, 8-, or 9-residue macrolactam ring; the C terminus is threaded through this ring and trapped by bulky side chains, thus stabilizing the entropically disfavored conformation (Fig. 1A) [9][10][11]13,[15][16][17][18][19][20][21][22][23][24].…”

Topoisomer Differentiation of Molecular Knots by FTICR MS: Lessons from Class II Lasso Peptides

“…In both peptides, the steric entrapping of the C-terminal tail in the macrolactam ring relies on the presence of a bulky amino acid located below the ring: Y20 for MccJ25 [20] and R15 for capistruin [21]. In addition, both peptides contain a bulky amino acid located above the ring: F19 for MccJ25 and R11 for capistruin.…”