Biology subjects

Booker, S.

Publications and source records attributed to Booker, S..

9 recordsLinked to original sources

bioRxiv2026

A Synthetic Archaeal Lipid Analog Enables Quantification of Substrate, Products, and Intermediates in the Tetraether Synthase Reaction

Glycerol dibiphytanyl glycerol tetraether (GDGT) and macrocyclic diether lipids (mAG) are unique membrane lipids predominantly found in archaea. Both lipids are composed of the same structural components: polar headgroups, glycerol backbones, and ether-linked 40-carbon biphytanyl chains. Tes, a member of the radical S-adenosylmethionine enzyme superfamily, synthesizes the biphytanyl chain by catalyzing carbon-carbon (C-C) bond formation between the terminal carbons of two phytanyl chains of the saturated diether lipid substrate. The coupling between the termini of two phytanyl chains on one glycerophospholipid yields mAG, whereas two couplings between the phytanyl termini of two glycerophospholipids yield GDGT. Quantification of the products and presumed intermediates formed during this multistep reaction has been challenging using mass spectrometry due to the lack of appropriate standards for each species. Herein, we designed and synthesized a diether lipid substrate analog containing a fluorescent/UV-visible tag linked to the headgroup, enabling the quantification of each species formed during a Tes reaction. Importantly, under laboratory conditions at 45 degrees C, we report that GDGT and mAG are initially formed in a 1:1.65 ratio, which differs considerably from the previously assumed ratio.

biochemistry↗

bioRxiv2026

Amino Acids in the RSSY Motif of Lipoyl Synthase Control Substrate Binding and Reactivity

The last step in the biosynthesis of the lipoyl cofactor (LipCo) is the addition of two sulfur atoms at C6 and C8 of an n-octanoyl chain attached in an amide linkage to a target lysyl residue of a lipoyl carrier protein. This reaction is catalyzed by lipoyl synthase, a member of the radical S-adenosylmethionine (SAM) superfamily. Lipoyl synthase requires two [4Fe-4S] clusters. One cluster is used to cleave SAM reductively to generate two 5'-deoxyadenosyl 5'-radicals (5'-dA*), which abstract the C6 and C8 hydrogen atoms (H*) of the substrate in two sequential steps. The second cluster, termed the auxiliary cluster, is consumed during turnover to provide the attached sulfur atoms. The auxiliary cluster is ligated by three cysteines in a CX4CX5C motif and one serine residue (Ser308 in Escherichia coli) in a highly conserved R306SS308Y motif in the C-terminal region of the protein. Here, we show that Arg306 and Ser308 are absolutely required for LipCo formation. Substitution of Arg306 with Lys results in an essentially inactive protein due to poor substrate binding and positioning in the active site. Multiple substitutions of Ser308 were engineered. Most notable were the S308C and S308A variants, which greatly diminished LipCo formation. However, the S308C variant resulted in greater production of the 6-mercaptooctanoyl intermediate and the formation of a desaturated product, identified as a 6-octenoyl group. Furthermore, the 3Fe cluster formed during degradation of the auxiliary cluster during C6 sulfur substitution in the wild-type reaction is not observed with the S308C variant. Instead, the auxiliary cluster remains tetranuclear and forms a monothiolated cross-linked species with a high-spin, S = 7/2, configuration that decays to the 6-octenoyl-containing product. Other amino acids in the RSSY motif were not essential for catalysis. TOC Graphic O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=94 SRC="FIGDIR/small/727706v2_ufig2.gif" ALT="Figure 2"> View larger version (36K): org.highwire.dtl.DTLVardef@19e1f29org.highwire.dtl.DTLVardef@ff1e4org.highwire.dtl.DTLVardef@d1cf91org.highwire.dtl.DTLVardef@923d1d_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2026

Evidence for an Organometallic Species Formed in the ArsL Reaction

The radical S-adenosylmethionine (SAM) superfamily comprises over 800,000 unique sequences of enzymes that catalyze more than 100 distinct reactions. Canonical radical SAM (RS) enzymes are composed of a full or partial triose phosphate isomerase fold and contain a highly conserved CX3CX2C motif. The cysteines in the conserved motif ligate an [Fe4S4] cluster used in the reductive cleavage of SAM to yield methionine and a 5'-deoxyadenosyl 5'-radical (5'-dA*). The 5'-dA* is typically used to initiate catalysis by abstracting a hydrogen atom from a bound substrate, yielding 5'-deoxyadenosine and a substrate radical. ArsL, a recently characterized RS enzyme involved in the biosynthesis of the antibiotic arsinothricin (AST), catalyzes a reaction that deviates from the canonical RS reaction, forming methylthioadenosine and a 3-amino-3-carboxypropyl radical (ACP*). The ACP* is used to construct a carbon-arsenic bond to form the organoarsenic compound hydroxyarsinothricin (AST-OH), the penultimate enzymatic step in forming AST. While investigating how ArsL suppresses the formation of the 5'-dA* in favor of the ACP*, we discovered that ArsL forms a unique organometallic species containing a bond between the gamma carbon of ACP and the unique iron of the [Fe4S4] cluster. We propose that ArsL uses this novel species to generate a sufficiently electrophilic carbon that can be attacked by arsenous acid, thereby forming the carbon-arsenic bond.

biochemistry↗

bioRxiv2026

Isolation and In vitro Characterization of BchE, the Cobalamin-Dependent Anaerobic Magnesium Protoporphyrin IX Monomethylester Cyclase Involved in Bacteriochlorophyll Biosynthesis

The radical S-adenosylmethionine (SAM) superfamily comprises more than 800,000 enzymes that use [Fe4S4] clusters to initiate radical chemistry that mediates an exceptionally broad range of chemical transformations. Within this superfamily, cobalamin (Cbl)-dependent radical SAM enzymes constitute a major subclass predominantly associated with methylation reactions. However, several notable members catalyze non-methylase reactions, for which the mechanistic role of Cbl is poorly understood. Bacteriochlorophyll biosynthesis enzyme BchE is a Cbl-dependent radical SAM enzyme that catalyzes a six-electron oxidation of Mg-protoporphyrin IX monomethylester (MPE) to protochlorophyllide (PChlide), installing a ketone and forming the fifth ring of bacteriochlorophyll under anaerobic conditions. Although prior in vivo and in vitro studies have demonstrated a requirement for Cbl, SAM, and a low-potential reductant, detailed mechanistic analysis has been impeded by the inability to obtain soluble, catalytically active enzyme. Here, we report the successful isolation and spectroscopic characterization of BchE, enabling the first in vitro reconstitution of its enzymatic activity. Using both chemical and biological reducing systems, we observe the formation of PChlide along with proposed reaction intermediates and several off-pathway products. These results provide new insight into the oxidative chemistry mediated by Cbl in non-methylase radical SAM enzymes and establish BchE as a tractable model for elucidating how cobalamin is deployed in this understudied subclass. Significance StatementBacteriochlorophyll biosynthesis enzyme BchE is a cobalamin-dependent radical SAM enzyme that catalyzes a six-electron oxidation of Mg-protoporphyrin IX monomethylester (MPE) in the absence of molecular oxygen. This reaction entails the oxidation of carbon 131 from a methylene to a ketone and the formation of a carbon-carbon bond between carbons 132 and 15 to generate bacteriochlorophylls fifth ring. How BchE performs this reaction has remained mysterious since its identification in the early 2000s, largely because it has been refractory to purification and in vitro characterization. This work describes the first purification of BchE, its spectroscopic characterization, and biochemical studies, providing key mechanistic insight and information on the likely state of cobalamin during the reaction.

biochemistry↗

bioRxiv2026

Structural Basis for C8 methylation of 23S ribosomal RNA by Cfr

Cfr methylates C8 of adenosine 2503 (A2503) in 23S ribosomal RNA (rRNA) and will also methylate C2 of A2503 after methylating C8. C8 methylation confers resistance to more than five classes of clinically used antibiotics, highlighting it as a worrisome mechanism of antibiotic resistance. Here, we report the structure of Cfr, determined by cryogenic electron microscopy (Cryo-EM). Despite its small size ([~]36 kDa), we exploit a transient protein-RNA crosslink that forms during catalysis, which requires Cys105 to resolve. Using a Cfr Cys105Ala variant and an 87-nucleotide strand of rRNA, we isolate the crosslinked species and determine its structure to 3.0 [A] resolution. Notably, the 87-mer rRNA adopts an L-shaped conformation characteristic of tRNAs, rather than the conformation it assumes in the ribosome. One Sentence SummaryCryo-EM structure of Cfr, a radical S-adenosylmethionine methylase that confers antibiotic resistance

biochemistry↗

bioRxiv2024

Typical development of synaptic and neuronal properties can proceed without microglia

Brain-resident macrophages, microglia, have been proposed to play an active role in synaptic refinement and maturation, influencing plasticity and circuit-level connectivity. Here we show that a variety of neurodevelopmental processes previously attributed to microglia can proceed without them. Using a genetically modified mouse which lacks microglia (Csf1r{Delta}FIRE/{Delta}FIRE) we find that intrinsic properties, synapse number and synaptic maturation are largely normal in the hippocampal CA1 region and somatosensory cortex at stages where microglia have been implicated. Seizure susceptibility and hippocampal-prefrontal cortex coherence in awake behaving animals, processes disrupted in mice deficient in microglia-enriched genes, are also normal. Similarly, eye-specific segregation of inputs into the lateral geniculate nucleus proceeds normally in the absence of microglia. Single cell/nucleus transcriptomic analyses of neurons and astrocytes did not uncover any substantial perturbation due to microglial absence. Thus, the brain possesses remarkable adaptability to execute developmental synaptic refinement, maturation and connectivity in the absence of microglia.

neuroscience↗

bioRxiv2021

Structural basis for carbapenam C-alkylation by TokK, a B12-dependent radical SAM enzyme

Cobalamin- or B12-dependent radical S-adenosylmethionine (SAM) enzymes acting during carbapenem antibiotic biosynthesis carry out radical-mediated methyl transfers that underlie the therapeutic usefulness of these essential medicines. Here we present x-ray crystal structures of TokK, which are representative of this functional class, containing its two metallocofactors and determined in the presence and absence of carbapenam substrate. The structures give the first visualization of a cobalamin-dependent radical SAM methylase that employs the radical mechanism shared by a vast majority of these enzymes. The structures provide insight into the stereochemistry of initial C6 methylation and suggests that substrate positioning governs the rate of each methylation event. One Sentence SummaryStructural insight into a cobalamin-dependent radical SAM methylase that performs three sequential radical-mediated methylations to install the C6 side chain of a carbapenem antibiotic.

biochemistry↗

bioRxiv2019

LAB-AID (Laboratory Automated Interrogation of Data): an interactive web application for visualization of multi-level data from biological experiments

A key step in understanding the results of biological experiments is visualization of the data. Many laboratory experiments contain a range of measurements that exist within a hierarchy of interdependence. An automated way to visualise and interrogate experimental data would: 1) lead to improved understanding of the results, 2) help to determine which statistical tests should be performed, and 3) easily identify outliers and sources of batch effects. Unfortunately, existing graphing solutions often demand expertise in programming, require considerable effort to import and examine such multi-level data, or are unnecessarily complex for the task at hand. Here we present LAB-AID (Laboratory Automated Interrogation of Data), an interactive tool specifically designed to automatically visualize and query hierarchical data resulting from biological experiments.

bioinformatics↗

bioRxiv2018

Cellular and Synaptic Phenotype Compensations Limit Circuit Disruption in Fmr1-KO Mouse Layer 4 Barrel Cortex but Fail to Prevent Deficits in Information Processing

Sensory hypersensitivity is a common and debilitating feature of neurodevelopmental disorders such as Fragile X Syndrome (FXS). However, how developmental changes in neuronal function ultimately culminate in the network dysfunction that underlies sensory hypersensitivities is not known. To address this, we studied the layer 4 barrel cortex circuit in Fmr1 knockout mice, a critical sensory processing circuit in this mouse model of FXS. By systematically studying cellular and synaptic properties of layer 4 neurons and combining with cellular and network simulations, we explored how the array of phenotypes in Fmr1 knockout produce circuit pathology during development that result in sensory processing dysfunction. We show that many of the cellular and synaptic pathologies in Fmr1 knockout mice are antagonistic, mitigating circuit dysfunction, and hence can be regarded as compensatory to the primary pathology. Despite this compensation, the layer 4 network in the Fmr1 knockout exhibits significant alterations in spike output in response to ascending thalamocortical input that we show results in impaired sensory encoding. We suggest that it is this developmental loss of layer 4 sensory encoding precision that drives subsequent developmental alterations in layer 4 - layer 2/3 connectivity and plasticity observed in the Fmr1 knockout, and is a critical process producing sensory hypersensitivity.

neuroscience↗