All Publications

  • Structural and mechanistic analysis of Ca2+-dependent regulation of transglutaminase 2 activity using a Ca2+-bound intermediate state. Proceedings of the National Academy of Sciences of the United States of America Sewa, A. S., Besser, H. A., Mathews, I. I., Khosla, C. 2024; 121 (28): e2407066121

    Abstract

    Mammalian transglutaminases, a family of Ca2+-dependent proteins, are implicated in a variety of diseases. For example, celiac disease (CeD) is an autoimmune disorder whose pathogenesis requires transglutaminase 2 (TG2) to deamidate select glutamine residues in diet-derived gluten peptides. Deamidation involves the formation of transient gamma-glutamyl thioester intermediates. Recent studies have revealed that in addition to the deamidated gluten peptides themselves, their corresponding thioester intermediates are also pathogenically relevant. A mechanistic understanding of this relevance is hindered by the absence of any structure of Ca2+-bound TG2. We report the X-ray crystallographic structure of human TG2 bound to an inhibitory gluten peptidomimetic and two Ca2+ ions in sites previously designated as S1 and S3. Together with additional structure-guided experiments, this structure provides a mechanistic explanation for how S1 regulates formation of an inhibitory disulfide bond in TG2, while also establishing that S3 is essential for gamma-glutamyl thioester formation. Furthermore, our crystallographic findings and associated analyses have revealed that i) two interacting residues, H305 and E363, play a critical role in resolving the thioester intermediate into an isopeptide bond (transamidation) but not in thioester hydrolysis (deamidation); and ii) residues N333 and K176 stabilize preferred TG2 substrates and inhibitors via hydrogen bonding to nonreactive backbone atoms. Overall, the intermediate-state conformer of TG2 reported here represents a superior model to previously characterized conformers for both transition states of the TG2-catalyzed reaction.

    View details for DOI 10.1073/pnas.2407066121

    View details for PubMedID 38959038

  • Enterocyte-derived and catalytically active transglutaminase 2 in the gut lumen of mice: Implications for celiac disease. Gastroenterology Meling, M. T., Kleppa, L., Besser, H. A., Khosla, C., du Pré, M. F., Sollid, L. M. 2024

    View details for DOI 10.1053/j.gastro.2024.05.029

    View details for PubMedID 38825048

  • Celiac disease: mechanisms and emerging therapeutics. Trends in pharmacological sciences Besser, H. A., Khosla, C. 2023

    Abstract

    Celiac disease (CeD) is a widespread, gluten-induced, autoimmune disorder that lacks any medicinal therapy. Towards the goal of developing non-dietary treatments for CeD, research has focused on elucidating its molecular and cellular etiology. A model of pathogenesis has emerged centered on interactions between three molecular families: specific class II MHC proteins on antigen-presenting cells (APCs), deamidated gluten-derived peptides, and T cell receptors (TCRs) on inflammatory CD4+ T cells. Growing evidence suggests that this pathogenic axis can be pharmacologically targeted to protect patients from some of the adverse effects of dietary gluten. Further studies have revealed the existence of additional host and environmental contributors to disease initiation and tissue damage. This review summarizes our current understanding of CeD pathogenesis and how it is being harnessed for therapeutic design and development.

    View details for DOI 10.1016/j.tips.2023.09.006

    View details for PubMedID 37839914

  • Targeted Lysosomal Degradation of Secreted and Cell Surface Proteins through the LRP-1 Pathway. Journal of the American Chemical Society Loppinet, E., Besser, H. A., Lee, C. E., Zhang, W., Cui, B., Khosla, C. 2023

    Abstract

    Protein dysregulation has been characterized as the cause of pathogenesis in many different diseases. For proteins lacking easily druggable pockets or catalytically active sites, targeted protein degradation is an attractive therapeutic approach. While several methods for targeted protein degradation have been developed, there remains a demand for lower molecular weight molecules that promote efficient degradation of their targets. In this work, we describe the synthesis and validation of a series of heterobifunctional molecules that bind a protein of interest through a small molecule ligand while targeting them to the lysosome using a short gluten peptide that leverages the TG2/LRP-1 pathway. We demonstrate that this approach can be used to effectively endocytose and degrade representative secreted, cell surface, and transmembrane proteins, notably streptavidin, the vitamin B12 receptor, cubilin, and integrin αvβ5. Optimization of these prototypical molecules could generate pharmacologically relevant LYTAC agents.

    View details for DOI 10.1021/jacs.3c05109

    View details for PubMedID 37590164

  • LRP-1 links post-translational modifications to efficient presentation of celiac disease-specific Tcell antigens. Cell chemical biology Loppinet, E., Besser, H. A., Sewa, A. S., Yang, F., Jabri, B., Khosla, C. 2022

    Abstract

    Celiac disease (CeD) is an autoimmune disorder in which gluten-derived antigens trigger inflammation. Antigenic peptides must undergo site-specific deamidation to be presentable to CD4+ Tcells in an HLA-DQ2 or -DQ8 restricted manner. While the biochemical basis for this post-translational modification is understood, its localization in the patient's intestine remains unknown. Here, we describe a mechanism by which gluten peptides undergo deamidation and concentration in the lysosomes of antigen-presenting cells, explaining how the concentration of gluten peptides necessary to elicit an inflammatory response in CeD patients is achieved. A ternary complex forms between a gluten peptide, transglutaminase-2 (TG2), and ubiquitous plasma protein alpha2-macroglobulin, and is endocytosed by LRP-1. The covalent TG2-peptide adduct undergoes endolysosomal decoupling, yielding the expected deamidated epitope. Our findings invoke a pathogenic role for dendritic cells and/or macrophages in CeD and implicate TG2 in the lysosomal clearance of unwanted self and foreign extracellular proteins.

    View details for DOI 10.1016/j.chembiol.2022.12.002

    View details for PubMedID 36608691

https://orcid.org/0000-0001-9361-7496