Biology subjects

Khavari, P.

Publications and source records attributed to Khavari, P..

6 recordsLinked to original sources

bioRxiv2025

Thermal proteome profiling identifies glucose binding proteins involved in metabolic disease

Recent work has shown that glucose can directly bind non-enzymatic proteins to modulate their function. We sought to build on this work by adapting thermal proteome profiling screens to uncover novel glucose interactors involved in metabolism. Proteome integral solubility alternation (PISA) profiling nominated 23 proteins with glucose-induced thermal solubility, including two proteins strongly implicated in metabolic disease, TSC22D4 and IGF2BP2. First, we characterized glucose binding of TSC22D4, an intrinsically disordered leucine zipper protein strongly implicated in hepatic steatosis. MST confirmed direct glucose-protein interaction of TSC22D4. UV-crosslinking mass spectrometry identified putative glucose binding at the C-terminal leucine zipper. Mutating isoleucine 322 to tryptophan (I322W) abolishes glucose binding. Crosslinking-MS and chemo-proteomic experiments suggest that glucose increases accessibility of the leucine zipper region, resulting in intra-protein contacts between C-terminal zipper domain and N-terminal intrinsically-disordered domain. TSC22D4 associates with fatty acid metabolism machinery proteins in response to high glucose conditions, suggesting a possible role for TSC22D4 in altering fatty acid metabolism. Next, we characterized glucose-binding in IGF2BP2, an RNA-binding protein essential for beta cell insulin secretion. We first confirmed direct IGF2BP2-glucose interaction and created glucose-binding mutant Y40A based on computational docking predictions. IGF2BP2Y40A exhibited a dominant negative impact on proliferation and insulin secretion in MIN6-6 beta cells. Glucose increased IGF2BP2 binding to client mRNAs Igf2 and Pdx1, which has previously been demonstrated to mediate its impact on insulin secretion. Thus, our data suggests that IGF2BP2 directly binds glucose to enhance insulin secretion.

biochemistry↗

bioRxiv2024

Disease-Linked Regulatory DNA Variants and Homeostatic Transcription Factors in Epidermis

Identifying noncoding single nucleotide variants (SNVs) in regulatory DNA linked to polygenic disease risk, the transcription factors (TFs) they bind, and the target genes they dysregulate is a goal in polygenic disease research. Massively parallel reporter gene analysis (MPRA) of 3,451 SNVs linked to risk for polygenic skin diseases characterized by disrupted epidermal homeostasis identified 355 differentially active SNVs (daSNVs). daSNV target gene analysis, combined with daSNV editing, underscored dysregulated epidermal differentiation as a pathomechanism shared across common polygenic skin diseases. CRISPR knockout screens of 1772 human TFs revealed 108 TFs essential for epidermal progenitor differentiation, uncovering novel roles for ZNF217, CXXC1, FOXJ2, IRX2 and NRF1. Population sampling CUT&RUN of 27 homeostatic TFs identified allele-specific DNA binding (ASB) differences at daSNVs enriched near epidermal homeostasis and monogenic skin disease genes, with notable representation of SP/KLF and AP-1/2 TFs. This resource implicates dysregulated differentiation in risk for diverse polygenic skin diseases.

genetics↗

bioRxiv2024

irCLIP-RNP and Re-CLIP reveal patterns of dynamic protein associations on RNA

RNA binding proteins (RBPs) control varied processes, including RNA splicing, stability, transport, and translation1-3. Dysfunctional RNA-RBP interactions contribute to the pathogenesis of human disease1,4,5, however, characterizing the nature and dynamics of multiprotein assemblies on RNA has been challenging. To address this, non-isotopic ligation-based ultraviolet crosslinking immunoprecipitation6 was combined with mass spectrometry (irCLIP-RNP) to identify RNA-dependent associated proteins (RDAPs) co-bound to RNA with any RBP of interest. irCLIP-RNP defined landscapes of multimeric protein assemblies on RNA, uncovering previously unknown patterns of RBP-RNA associations, including cell-type-selective combinatorial relationships between RDAPs and primary RBPs. irCLIP-RNP also defined dynamic RDAP remodeling in response to epidermal growth factor (EGF), uncovering EGF-induced recruitment of UPF1 adjacent to HNRNPC to effect splicing surveillance of cell proliferation mRNAs. To identify the RNAs simultaneously co-bound by multiple studied RBPs, a sequential immunoprecipitation irCLIP (Re-CLIP) method was also developed. Re-CLIP confirmed binding relationships seen in irCLIP-RNP and detected simultaneous HNRNPC and UPF1 co-binding on RND3 and DDX3X mRNAs. irCLIP-RNP and Re-CLIP provide a framework to identify and characterize dynamic RNA-protein assemblies in living cells.

molecular biology↗

bioRxiv2024

Mitochondrial Raf1 Regulates Glutamine Catabolism

One-Sentence SummaryRaf1 is present within the mitochondrial matrix, where it binds GLS to regulate glutamine catabolism and tumorigenesis. In cancer, Raf1 activation occurs via mechanisms that include mutation of upstream regulators, such as receptor tyrosine kinases and Ras GTPases, as well as by mutations that affect RAF1 itself, including via gene amplification (1-4). Once recruited to the plasma membrane (PM) Raf1 can engage downstream mitogen-activated protein kinase (MAPK) pathway signaling through phosphorylation of the MEK kinases (5). In addition to Raf1, A-Raf and B-Raf can also activate MEK and these other two Raf isoforms can compensate for MAPK activation in the event of Raf1 loss (6, 7). Despite this, Raf1 remains essential for the development and maintenance of some tumors through mechanisms independent of MAPK activity (7, 8). In this regard, Raf1 has well-described interactions outside the canonical MAPK pathway, including several with outer mitochondrial membrane (OMM) proteins (9, 10), although Raf1 has not been previously identified inside mitochondria. Mitochondria comprise a hub for various metabolic processes modulated in cancer cells to accommodate rapid proliferation. One such process is glutaminolysis, which involves the catabolism of glutamine to generate both ATP as well as precursors for the synthesis of fatty acids, nucleotides, and nonessential amino acids (11-13). Glutaminase (GLS) proteins, which catalyze the first and rate-limiting step of this process by converting glutamine to glutamate, are often upregulated in cancer (14-16). GLS activation has been previously associated with tumors driven by Ras, upstream regulators of Raf kinases (13, 17). Here we identify Raf1 protein inside mitochondria where Raf1 associates with GLS in the mitochondrial matrix to enable glutamine catabolism and tumorigenic growth. Raf kinases play vital roles in normal mitogenic signaling and cancer, however, the identities of functionally important Raf-proximal proteins throughout the cell are not fully known. Raf1 proximity proteomics/BioID in Raf1-dependent cancer cells unexpectedly identified Raf1-adjacent proteins known to reside in the mitochondrial matrix. Inner-mitochondrial localization of Raf1 was confirmed by mitochondrial purification and super-resolution microscopy. Inside mitochondria, Raf1 associated with glutaminase (GLS) in diverse human cancers and enabled glutaminolysis, an important source of biosynthetic precursors in cancer. These impacts required Raf1 kinase activity and were independent of canonical MAP kinase pathway signaling. Kinase-dead mitochondrial matrix-localized Raf1 impaired glutaminolysis and tumorigenesis in vivo. These data indicate that Raf1 localizes inside mitochondria where it interacts with GLS to engage glutamine catabolism and support tumorigenesis.

cancer biology↗

bioRxiv2021

The proximal proteome of 17 SARS-CoV-2 proteins links to disrupted antiviral signaling and host translation

Viral proteins localize within subcellular compartments to subvert host machinery and promote pathogenesis. To study SARS-CoV-2 biology, we generated an atlas of 2422 human proteins vicinal to 17 SARS-CoV-2 viral proteins using proximity proteomics. This identified viral proteins at specific intracellular locations, such as association of accessary proteins with intracellular membranes, and projected SARS-CoV-2 impacts on innate immune signaling, ER-Golgi transport, and protein translation. It identified viral protein adjacency to specific host proteins whose regulatory variants are linked to COVID-19 severity, including the TRIM4 interferon signaling regulator which was found proximal to the SARS-CoV-2 M protein. Viral NSP1 protein adjacency to the EIF3 complex was associated with inhibited host protein translation whereas ORF6 localization with MAVS was associated with inhibited RIG-I 2CARD-mediated IFNB1 promoter activation. Quantitative proteomics identified candidate host targets for the NSP5 protease, with specific functional cleavage sequences in host proteins CWC22 and FANCD2. This data resource identifies host factors proximal to viral proteins in living human cells and nominates pathogenic mechanisms employed by SARS-CoV-2. Author SummarySARS-CoV-2 is the latest pathogenic coronavirus to emerge as a public health threat. We create a database of proximal host proteins to 17 SARS-CoV-2 viral proteins. We validate that NSP1 is proximal to the EIF3 translation initiation complex and is a potent inhibitor of translation. We also identify ORF6 antagonism of RNA-mediate innate immune signaling. We produce a database of potential host targets of the viral protease NSP5, and create a fluorescence-based assay to screen cleavage of peptide sequences. We believe that this data will be useful for identifying roles for many of the uncharacterized SARS-CoV-2 proteins and provide insights into the pathogenicity of new or emerging coronaviruses.

microbiology↗

bioRxiv2021

SARS-CoV-2 B.1.1.7 and B.1.351 Spike variants bind human ACE2 with increased affinity

SARS-CoV2 being highly infectious has been particularly effective in causing widespread infection globally and more variants of SARS-CoV2 are constantly being reported with increased genomic surveillance. In particular, the focus is on mutations of Spike protein, which binds human ACE2 protein enabling SARS-CoV2 entry and infection. Here we present a rapid experimental method leveraging the speed and flexibility of Mircoscale Thermopheresis (MST) to characterize the interaction between Spike Receptor Binding Domain (RBD) and human ACE2 protein. The B.1.351 variant harboring three mutations, (E484K, N501Y, and K417N) binds the ACE2 at nearly five-fold greater affinity than the original SARS-COV-2 RBD. We also find that the B.1.1.7 variant, binds two-fold more tightly to ACE2 than the SARS-COV-2 RBD.

pathology↗