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1. Biophysical characterization of the CXC chemokine receptor 2 ligands

   https://doi.org/10.1371/journal.pone.0298418  

   Martin, Patrick; Kurth, Emily A; Budean, David; Momplaisir, Nathalie; Qu, Elaine; Simien, Jennifer M; Orellana, Grace E; Brautigam, Chad A; Smrcka, Alan V; Haglund, Ellinor (April 2024, PLOS ONE)

   Jeyaseelan, Samithamby (Ed.)

   The chemokines of the immune system act as first responders by operating as chemoattractants, directing immune cells to specific locations of inflamed tissues. This promiscuous network is comprised of 50 ligands and 18 receptors where the ligands may interact with the receptors in various oligomeric states i.e., monomers, homodimers, and heterodimers. Chemokine receptors are G-protein coupled receptors (GPCRs) present in the membrane of immune cells. The migration of immune cells occurs in response to a concentration gradient of the ligands. Chemotaxis of neutrophils is directed by CXC-ligand (CXCL) activation of the membrane bound CXC chemokine receptor 2 (CXCR2). CXCR2 plays an important role in human health and is linked to disorders such as autoimmune disorders, inflammation, and cancer. Yet, despite their important role, little is known about the biophysical characteristics controlling ligand:ligand and ligand:receptor interaction essential for biological activity. In this work, we study the homodimers of three of the CXCR2 cognate ligands, CXCL1, CXCL5, and CXCL8. The ligands share high structural integrity but a low sequence identity. We show that the sequence diversity has evolved different binding affinities and stabilities for the CXC-ligands resulting in diverse agonist/antagonist behavior. Furthermore, CXC-ligands fold through a three-state mechanism, populating a folded monomeric state before associating into an active dimer. 

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2. Inverting angiogenesis with interstitial flow and chemokine matrix-binding affinity

   https://doi.org/10.1038/s41598-022-08186-0  

   Moure, Adrian; Vilanova, Guillermo; Gomez, Hector (March 2022, Scientific Reports)

   Abstract The molecular signaling pathways that orchestrate angiogenesis have been widely studied, but the role of biophysical cues has received less attention. Interstitial flow is unavoidable in vivo, and has been shown to dramatically change the neovascular patterns, but the mechanisms by which flow regulates angiogenesis remain poorly understood. Here, we study the complex interactions between interstitial flow and the affinity for matrix binding of different chemokine isoforms. Using a computational model, we find that changing the matrix affinity of the chemokine isoform can invert the effect of interstitial flow on angiogenesis—from preferential growth in the direction of the flow when the chemokine is initially matrix-bound to preferential flow against the flow when it is unbound. Although fluid forces signal endothelial cells directly, our data suggests a mechanism for the inversion based on biotransport arguments only, and offers a potential explanation for experimental results in which interstitial flow produced preferential vessel growth with and against the flow. Our results point to a particularly intricate effect of interstitial flow on angiogenesis in the tumor microenvironment, where the vessel network geometry and the interstitial flow patterns are complex. 

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3. Switchable Membrane Remodeling and Antifungal Defense by Metamorphic Chemokine XCL1

   https://doi.org/10.1021/acsinfecdis.0c00011  

   Dishman, Acacia F.; Lee, Michelle W.; de Anda, Jaime; Lee, Ernest Y.; He, Jie; Huppler, Anna R.; Wong, Gerard C. L.; Volkman, Brian F. (April 2020, ACS Infectious Diseases)
4. Exploring Chemokine Homodimer Stability: Structural Insights into CXC and CC Interfaces

   https://doi.org/10.3390/biophysica4040037  

   Budean, David; Almeida-Hernández, Yasser; Pandey, Jitendra; Pérez, Joel Mieres; Sánchez_García, Elsa; Haglund, Ellinor (December 2024, Biophysica)

   Chemokine ligands play a pivotal role in immune response by mediating cell migration and coordinating cellular processes through interactions with chemokine receptors. Understanding their sequence and structural integrity is crucial for elucidating their biological functions and potential therapeutic applications. In this study, we investigate the dimer interface between two distinct homodimer topologies: CXC and CC homodimers. Despite nearly identical monomeric structures, the rigid CXC interface is characterized by interactions between the N-loop/β-sheet regions, while the more flexible CC interface involves interactions through the unstructured N-terminal regions. Our structural and biophysical analyses indicate no significant differences in the free energy of folding (2–8 kcal/mol) and binding (10–14 kcal/mol) between the two homodimer topologies, showing that their free energy is primarily driven by sequence. We hypothesize that the biological signal is driven by the malleability of the dimer, depending on the binding interface. Understanding these structural dynamics opens new possibilities for designing chemokine-based therapeutics to modulate immune responses in diseases such as cancer, inflammation, and autoimmune disorders. 

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5. Engineered endosymbionts that alter mammalian cell surface marker, cytokine and chemokine expression

   https://doi.org/10.1038/s42003-022-03851-6  

   Madsen, Cody S.; Makela, Ashley V.; Greeson, Emily M.; Hardy, Jonathan W.; Contag, Christopher H. (December 2022, Communications Biology)

   Abstract Developing modular tools that direct mammalian cell function and activity through controlled delivery of essential regulators would improve methods of guiding tissue regeneration, enhancing cellular-based therapeutics and modulating immune responses. To address this challenge, Bacillus subtilis was developed as a chassis organism for engineered endosymbionts (EES) that escape phagosome destruction, reside in the cytoplasm of mammalian cells, and secrete proteins that are transported to the nucleus to impact host cell response and function. Two synthetic operons encoding either the mammalian transcription factors Stat-1 and Klf6 or Klf4 and Gata-3 were recombined into the genome of B. subtilis expressing listeriolysin O (LLO) from Listeria monocytogenes and expressed from regulated promoters. Controlled expression of the mammalian proteins from B. subtilis LLO in the cytoplasm of J774A.1 macrophage/monocyte cells altered surface marker, cytokine and chemokine expression. Modulation of host cell fates displayed some expected patterns towards anti- or pro-inflammatory phenotypes by each of the distinct transcription factor pairs with further demonstration of complex regulation caused by a combination of the EES interaction and transcription factors. Expressing mammalian transcription factors from engineered intracellular B. subtilis as engineered endosymbionts comprises a new tool for directing host cell gene expression for therapeutic and research purposes. 

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