Biology subjects

Zelinskaya, N.

Publications and source records attributed to Zelinskaya, N..

5 recordsLinked to original sources

bioRxiv2026

E. coli RsmF activity depends on prior modification of 16S rRNA helix 44

Bacterial ribosomal RNA (rRNA) methylations are important for accurate translation. Four distinct methylations incorporated by RsmE, RsmF, and RsmH/ RsmI form a cluster of three modified 16S rRNA nucleotides (m3U1498, m5C1407, and m4Cm1402) surrounding the decoding center of the 30S subunit. Given their common substrate requirement of a late-stage intermediate 30S subunit, these enzymes likely act contemporaneously during subunit biogenesis, but whether there exists a required modification order is unknown. Here, using hypomethylated 30S subunits obtained from a collection of rsmH/I/E/F-deleted Escherichia coli strains, we identify RsmF activity to be highly dependent on prior modification of h44 both in vitro and in E. coli. RsmF activity on hypomethylated 30S subunits could be partially rescued by prior in vitro methylation using RsmE and RsmH, indicating that incorporation of these methyl groups directly shapes h44 for recognition by RsmF. RNA structure probing using SHAPE-MaP and molecular dynamics simulations reveal specific alterations in 16S rRNA structure and dynamics in the absence of the m4C1402 (RsmH) and m3U1498 (RsmE) modifications that likely restrict RsmF action. These studies thus uncover a previously unappreciated "order of operations" for 16S rRNA modification during ribosome biogenesis with important implications for studies on the collective functions of these modifications. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=57 SRC="FIGDIR/small/736617v1_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@f843cborg.highwire.dtl.DTLVardef@12acb13org.highwire.dtl.DTLVardef@7a8d9eorg.highwire.dtl.DTLVardef@1e7aa5f_HPS_FORMAT_FIGEXP M_FIG C_FIG Key PointsO_LI16S rRNA C1407 modification by RsmF depends on the prior action of RsmE and RsmH in E. coli C_LIO_LIm5C1402/ m3U1498 alter 16S rRNA nucleotide dynamics creating a 30S substrate suitable for RsmF C_LIO_LIAn order of operations exists for h44 modifying enzymes acting at the 30S subunit decoding center C_LI

biochemistry↗

bioRxiv2025

Mechanism of 30S subunit recognition and modification by the conserved bacterial ribosomal RNA methyltransferase RsmI

Ribosomal RNA (rRNA) modifications are important for ribosome function and can influence bacterial susceptibility to ribosome-targeting antibiotics. The universally conserved 16S rRNA nucleotide C1402, for example, is the only 2-O-methylated nucleotide in the bacterial small (30S) ribosomal subunit and this modification fine tunes the shape and structure of the peptidyl tRNA binding site. The Cm1402 modification is incorporated by the conserved bacterial 16S rRNA methyltransferase RsmI, but it is unclear how RsmI is able to recognize its 30S substrate and specifically modify its buried target nucleotide. We determined a 2.42 [A] resolution cryo-EM structure of the RsmI-30S complex and, with accompanying functional analyses, show that RsmI anchors itself to the 30S subunit through multiple contacts with a conserved 16S rRNA surface previously only seen in the assembled subunit. This positions RsmI to induce an extensive h44 distortion to access C1402 that is unprecedented among 16S rRNA methyltransferases characterized to date. These analyses also reveal an essential contribution to 30S subunit interaction made by the previously structurally uncharacterized RsmI C-terminal domain, RsmI-induced RNA-RNA interactions with C1402, and an unappreciated dependence on a divalent metal ion for activity that suggests RsmI may be first of a distinct class of metal- and SAM-dependent RNA O-methyltransferases. This study significantly expands our mechanistic understanding of how intrinsic bacterial methyltransferases like RsmI modify their rRNA targets. Further, recognition of distant ribosome features and extensive unfolding of a critical rRNA functional center point to a potential role in accurate 30S subunit biogenesis.

biochemistry↗

bioRxiv2023

30S subunit recognition and G1405 modification by the aminoglycoside-resistance 16S ribosomal RNA methyltransferase RmtC

Acquired ribosomal RNA (rRNA) methylation has emerged as a significant mechanism of aminoglycoside resistance in pathogenic bacterial infections. Modification of a single nucleotide in the ribosome decoding center by the aminoglycoside-resistance 16S rRNA (m7G1405) methyltransferases effectively blocks the action of all 4,6-deoxystreptamine ring-containing aminoglycosides, including the latest generation of drugs. To define the molecular basis of 30S subunit recognition and G1405 modification by these enzymes, we used a S-adenosyl-L-methionine (SAM) analog to trap the complex in a post-catalytic state to enable determination of an overall 3.0 [A] cryo-electron microscopy structure of the m7G1405 methyltransferase RmtC bound to the mature Escherichia coli 30S ribosomal subunit. This structure, together with functional analyses of RmtC variants, identifies the RmtC N-terminal domain as critical for recognition and docking of the enzyme on a conserved 16S rRNA tertiary surface adjacent to G1405 in 16S rRNA helix 44 (h44). To access the G1405 N7 position for modification, a collection of residues across one surface of RmtC, including a loop that undergoes a disorder to order transition upon 30S subunit binding, induces significant distortion of h44. This distortion flips G1405 into the enzyme active site where it is positioned for modification by two almost universally conserved RmtC residues. These studies expand our understanding of ribosome recognition by rRNA modification enzymes and present a more complete structural basis for future development of strategies to inhibit m7G1405 modification to re-sensitize bacterial pathogens to aminoglycosides. SignificanceIncreasing prevalence of bacterial antibiotic resistance threatens our ability to treat bacterial infections and with it, many other facets of modern healthcare. For the ribosome-targeting aminoglycoside antibiotics, diverse pathogenic bacteria have acquired ribosomal RNA (rRNA) methyltransferase enzymes that confer exceptionally high-level resistance through site-specific modification of the drug binding site. Here, we define the molecular basis for ribosomal substrate recognition and modification by an enzyme (RmtC) representing the most clinically prevalent methyltransferase family. Specifically, RmtC exploits a conserved rRNA surface for binding and induces significant disruption of the rRNA structure to capture the target nucleotide for modification via a "base flipping" mechanism. These insights also present a platform for methyltransferase inhibitor development to extend usefulness of aminoglycoside antibiotics.

biochemistry↗

bioRxiv2021

50S subunit recognition and modification by the Mycobacterium tuberculosis ribosomal RNA methyltransferase TlyA

Changes in bacterial ribosomal RNA methylation status can alter the activity of diverse groups of ribosome-targeting antibiotics. These modifications are typically incorporated by a single methyltransferase that acts on one nucleotide target and rRNA methylation directly prevents drug binding, thereby conferring drug resistance. Loss of intrinsic methylation can also result in antibiotic resistance. For example, Mycobacterium tuberculosis becomes sensitized to tuberactinomycin antibiotics, such as capreomycin and viomycin, due to the action of the intrinsic methyltransferase TlyA. TlyA is unique among antibiotic resistance-associated methyltransferases as it has dual 16S and 23S rRNA substrate specificity and can incorporate cytidine-2-O-methylations within two structurally distinct contexts. Here, we report the structure of a mycobacterial 50S subunit-TlyA complex trapped in a post-catalytic state with a S-adenosyl-L-methionine analog using single-particle cryogenic electron microscopy. Together with complementary functional analyses, this structure reveals critical roles in 23S rRNA substrate recognition for conserved residues across an interaction surface that spans both TlyA domains. These interactions position the TlyA active site over the target nucleotide C2144 which is flipped from 23S Helix 69 in a process stabilized by stacking of TlyA residue Phe157 on the adjacent A2143. Base flipping may thus be a common strategy among rRNA methyltransferase enzymes even in cases where the target site is accessible without such structural reorganization. Finally, functional studies with 30S subunit suggest that the same TlyA interaction surface is employed to recognize this second substrate, but with distinct dependencies on essential conserved residues. Significance StatementThe bacterial ribosome is an important target for antibiotics used to treat infection. However, resistance to these essential drugs can arise through changes in ribosomal RNA (rRNA) modification patterns through the action of intrinsic or acquired rRNA methyltransferase enzymes. How these antibiotic resistance-associated enzymes recognize their ribosomal targets for site-specific modification is currently not well defined. Here, we uncover the molecular basis for large ribosomal (50S) subunit substrate recognition and modification by the Mycobacterium tuberculosis methyltransferase TlyA, necessary for optimal activity of the antitubercular drug capreomycin. From this work, recognition of complex rRNA structures distant from the site of modification and "flipping" of the target nucleotide base both emerge as general themes in ribosome recognition for bacterial rRNA modifying enzymes.

biochemistry↗

bioRxiv2019

Critical residues in the aminoglycoside-resistance 16S rRNA (m7G1405) methyltransferase RmtC play distinct roles in 30S substrate recognition

Methylation of the small ribosome subunit rRNA in the ribosomal decoding center results in exceptionally high-level aminoglycoside resistance in bacteria. Enzymes that methylate 16S rRNA on N7 of nucleotide G1405 (m7G1405) have been identified in both aminoglycoside-producing and clinically drug-resistant pathogenic bacteria. Using a fluorescence polarization 30S-binding assay and a new crystal structure of the methyltransferase RmtC at 3.14 [A] resolution, here we report a structure-guided functional study of 30S substrate recognition by the aminoglycoside resistance-associated 16S rRNA (m7G1405) methyltransferases. We found that the binding site for these enzymes in the 30S subunit directly overlaps with that of a second family of aminoglycoside resistance-associated 16S rRNA (m1A1408) methyltransferases, suggesting both groups of enzymes may exploit the same conserved rRNA tertiary surface for docking to the 30S. Within RmtC, we defined an N-terminal domain surface, comprising basic residues from both the N1 and N2 subdomains, that directly contributes to 30S-binding affinity. In contrast, additional residues lining a contiguous adjacent surface on the C-terminal domain were critical for 16S rRNA modification, but did not directly contribute to the binding affinity. The results from our experiments define the critical features of m7G1405 methyltransferase-substrate recognition and distinguish at least two distinct, functionally critical contributions of the tested enzyme residues: 30S-binding affinity and stabilizing a binding-induced 16S rRNA conformation necessary for G1405 modification. Our study sets the scene for future high-resolution structural studies of the 30S-methyltransferase complex and for potential exploitation of unique aspects of substrate recognition in future therapeutic strategies.

biochemistry↗