Biology subjects

Dorward, M.

Publications and source records attributed to Dorward, M..

5 recordsLinked to original sources

bioRxiv2025

LRRC58 defines an E3 ubiquitin ligase complex sensitive to cysteine abundance

Adaptation to fluctuating nutrient supply is essential for organismal survival, but how cells sense and respond to changes in the abundance of many critical nutrients remains undefined. One such example is the amino acid cysteine, whose reactive thiol group is exploited for diverse cellular functions. Here, by characterizing the machinery required for the conditional degradation of cysteine dioxygenase type I (CDO1), the critical enzyme responsible for cysteine catabolism, we identify a Cul2 E3 ligase complex containing the uncharacterized substrate adaptor LRRC58 that is sensitive to cysteine abundance. When cysteine is replete, LRRC58 activity is restrained through auto-ubiquitination and proteasomal degradation; upon cysteine deprivation, LRRC58 is stabilized to permit CDO1 degradation. Through saturation mutagenesis stability profiling, we systematically validate a structural model of the CDO1-LRRC58 interaction and identify residues at the LRRC58 C-terminus required for cysteine-dependent instability. The LRRC58-mediated degradation of CDO1 is essential to prevent ferroptotic cell death under conditions of cysteine scarcity, and mutations in CDO1 which cause neurodevelopmental defects in humans encode dominant-active proteins refractory to LRRC58 recognition. Altogether, these data reveal the CDO1-LRRC58 axis as a critical regulator of cysteine homeostasis that safeguards neural development.

molecular biology↗

bioRxiv2025

BromoCatch: a self-labelling tag platform for protein analysis and live cell imaging

Visualizing and manipulating proteins in live cells is crucial for studying complex biological processes. Self-labelling protein (SLP) tags such as HaloTag and SNAP-tag can be fused to genes of interest to allow protein labelling in cells. Limitations including size of the tag and suboptimal fitness of reactivity motivate development of improved tools to enable rapid, specific and stable protein labelling. We present BromoCatch, a novel SLP platform based on a small [~]13 kDa bromodomain (BD) engineered with a nucleophilic cysteine for covalent ligand engagement. A structure-based designed library of 16 "bumped" binders bearing diverse electrophilic warheads was screened against two different cysteine mutants using differential scanning fluorimetry and intact protein mass spectrometry to monitor covalent complex formation. The para-acrylamide bumped derivative MR116 and the Brd4-BD2 double mutant L387A,E438C formed the most potent and stable adduct, and its binding mode through covalent modification was confirmed by an X-ray cocrystal structure solved to 1.3 [A] of resolution. BromoCatch exhibited potent and irreversible target engagement in cells through nanoBRET and residence time assays. Practicality and scope are further demonstrated through the design and proof-of-concept application of a biotinylated conjugate, PROTAC tag degraders, and fluorescent probes of both full-on and switch-on types for ex-cellulo and live-cell imaging. Together, we qualify BromoCatch as a novel, versatile and efficient protein labelling tool and technology platform. Its advantageous design features and kinetic fitness, and its modular design enabling diverse functionalities, are anticipated to usher a range of future applications and witness broad utility.

biochemistry↗

bioRxiv2024

NRBP1 pseudokinase binds to and activates the WNK pathway in response to osmotic stress

WNK family kinases are regulated by osmotic stress and control ion homeostasis by activating SPAK and OXSR1 kinases. Using a proximity ligation approach, we found that osmotic stress promotes the association of WNK1 with the NRBP1 pseudokinase and TSC22D2/4 adaptor proteins, results that are confirmed by immunoprecipitation and mass spectrometry and immunoblotting studies. NRBP1 pseudokinase is closely related to WNK isoforms and contains a R{Phi}-motif binding conserved C-terminal (CCT) domain, similar to the CCT domains in WNKs, SPAK and OXSR1. Knockdown or knock-out of NRBP1 markedly inhibited sorbitol-induced activation of WNK1 and downstream components. We demonstrate recombinant NRBP1 can directly induce the activation of WNK4 in vitro. AlphaFold-3 modelling predicts that WNK1, SPAK, NRBP1, and TSC22D4 form a complex, in which two TSC22D4 R{Phi}-motifs interact with the CCTL1 domain of WNK1 and the CCT domain of NRBP1. Our data indicates NRBP1 functions as an upstream activator of the WNK pathway. TeaserNRBP1 functions as a scaffolding component regulating the assembly of a multi-subunit complex, required for the activation of the WNK Lysine Deficient Protein Kinase family in response to osmotic stress. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/628181v2_ufig1.gif" ALT="Figure 1"> View larger version (24K): org.highwire.dtl.DTLVardef@5b37eborg.highwire.dtl.DTLVardef@b4661corg.highwire.dtl.DTLVardef@19bc3e9org.highwire.dtl.DTLVardef@15b052e_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2020

Deciphering the LRRK code: LRRK1 and LRRK2 phosphorylate distinct Rab proteins and are regulated by diverse mechanisms

Much attention has focused on LRRK2, as autosomal dominant missense mutations that enhance its kinase activity cause inherited Parkinsons disease. LRRK2 regulates biology by phosphorylating a subset of Rab GTPases including Rab8A and Rab10 within its effector binding motif. In this study we explore whether LRRK1, a less studied homologue of LRRK2 that regulates growth factor receptor trafficking and osteoclast biology might also phosphorylate Rab proteins. Using mass spectrometry, we found that the endogenous Rab7A protein, phosphorylated at Ser72 was most impacted by LRRK1 knock-out. This residue is not phosphorylated by LRRK2 but lies at the equivalent site targeted by LRRK2 on Rab8A and Rab10. Accordingly, recombinant LRRK1 efficiently phosphorylated Rab7A at Ser72, but not Rab8A or Rab10. Employing a novel phospho-specific antibody, we found that phorbol ester stimulation of mouse embryonic fibroblasts markedly enhanced phosphorylation of Rab7A at Ser72 via LRRK1. We identify two LRRK1 mutations (K746G and I1412T), equivalent to the LRRK2 R1441G and I2020T Parkinsons mutations, that enhance LRRK1 mediated phosphorylation of Rab7A. We demonstrate that two regulators of LRRK2 namely Rab29 and VPS35[D620N], do not influence LRRK1. Widely used LRRK2 inhibitors do not inhibit LRRK1, but we identify a promiscuous Type-2 tyrosine kinase inhibitor termed GZD-824 that inhibits both LRRK1 and LRRK2. Finally, we show that interaction of Rab7A with its effector RILP is not affected by high stoichiometry LRRK1 phosphorylation. Altogether, these finding reinforce the idea that the LRRK enzymes have evolved as major regulators of Rab biology.

biochemistry↗

bioRxiv2019

PPM1H phosphatase counteracts LRRK2 signaling by selectively dephosphorylating Rab proteins

Mutations that activate LRRK2 protein kinase cause Parkinsons disease. LRRK2 phosphorylates a subset of Rab GTPases within their Switch-II motif controlling interaction with effectors. An siRNA screen of all protein phosphatases revealed that a poorly studied protein phosphatase, PPM1H, counteracts LRRK2 signaling by specifically dephosphorylating Rab proteins. PPM1H knock out increased endogenous Rab phosphorylation and inhibited Rab dephosphorylation. Overexpression of PPM1H suppressed LRRK2-mediated Rab phosphorylation. PPM1H also efficiently and directly dephosphorylated Rab8A in biochemical studies. A \"substrate-trapping\" PPM1H mutant (Asp288Ala) binds with high affinity to endogenous, LRRK2-phosphorylated Rab proteins, thereby blocking dephosphorylation seen upon addition of LRRK2 inhibitors. PPM1H is localized to the Golgi and its knockdown suppresses primary cilia formation, similar to pathogenic LRRK2. Thus, PPM1H acts as a key modulator of LRRK2 signaling by controlling dephosphorylation of Rab proteins. PPM1H activity enhancers could offer a new therapeutic approach to prevent or treat Parkinsons disease.

biochemistry↗