9on4
Crystal structure of Zn2+ bound Calprotectin variant I73K
Structural highlights
FunctionS10A8_HUMAN S100A8 is a calcium- and zinc-binding protein which plays a prominent role in the regulation of inflammatory processes and immune response. It can induce neutrophil chemotaxis and adhesion. Predominantly found as calprotectin (S100A8/A9) which has a wide plethora of intra- and extracellular functions. The intracellular functions include: facilitating leukocyte arachidonic acid trafficking and metabolism, modulation of the tubulin-dependent cytoskeleton during migration of phagocytes and activation of the neutrophilic NADPH-oxidase. Activates NADPH-oxidase by facilitating the enzyme complex assembly at the cell membrane, transfering arachidonic acid, an essential cofactor, to the enzyme complex and S100A8 contributes to the enzyme assembly by directly binding to NCF2/P67PHOX. The extracellular functions involve proinfammatory, antimicrobial, oxidant-scavenging and apoptosis-inducing activities. Its proinflammatory activity includes recruitment of leukocytes, promotion of cytokine and chemokine production, and regulation of leukocyte adhesion and migration. Acts as an alarmin or a danger associated molecular pattern (DAMP) molecule and stimulates innate immune cells via binding to pattern recognition receptors such as Toll-like receptor 4 (TLR4) and receptor for advanced glycation endproducts (AGER). Binding to TLR4 and AGER activates the MAP-kinase and NF-kappa-B signaling pathways resulting in the amplification of the proinflammatory cascade. Has antimicrobial activity towards bacteria and fungi and exerts its antimicrobial activity probably via chelation of Zn(2+) which is essential for microbial growth. Can induce cell death via autophagy and apoptosis and this occurs through the cross-talk of mitochondria and lysosomes via reactive oxygen species (ROS) and the process involves BNIP3. Can regulate neutrophil number and apoptosis by an anti-apoptotic effect; regulates cell survival via ITGAM/ITGB and TLR4 and a signaling mechanism involving MEK-ERK. Its role as an oxidant scavenger has a protective role in preventing exaggerated tissue damage by scavenging oxidants. Can act as a potent amplifier of inflammation in autoimmunity as well as in cancer development and tumor spread.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] Publication Abstract from PubMedCalprotectin is a heterodimer of the S100A8 and S100A9 EF-hand calcium binding proteins, which activates cell surface receptors that signal through the NF-kappaB inflammatory signaling pathway. Like all S100 proteins, calcium-induced conformational changes in calprotectin are required for binding to partner proteins. In the case of calprotectin, the addition of calcium correlates with the formation of a dimer of heterodimers (heterotetramer). Ligand-induced receptor oligomerization has been proposed as a mechanism of receptor activation. Conversely, it has also been suggested that calprotectin tetramerization can inhibit binding to receptors and serve as an autoinhibitory mechanism. In order to investigate the biological relevance of calprotectin tetramerization and facilitate in-depth biophysical and structural analysis, we have prepared three tetramerization-deficient variants: two single-site S100A8 mutations of hydrophobic isoleucine residues mediating the tetramer interface to lysine (I60K, I73K) and the corresponding double-site mutant (I60K/I70K). Dynamic light scattering, small-angle x-ray scattering, and nuclear magnetic resonance spectroscopy showed that all three tetramer-deficient variants remain as dimers in solution even in the presence of 40-fold excess calcium and undergo calcium-induced conformational changes. The crystal structure of I73K was determined to atomic-level resolution and confirms that the mutations cause only subtle, localized effects on the structure. Together, the results indicate that these tetramerization-deficient mutants will be useful reagents for discerning the functional role of calprotectin oligomerization in the activation of inflammatory receptors. Design and characterization of calprotectin tetramerization variants for probing the role of oligomerization in receptor activation.,Garcia V, D'Souza A, Kozlyuk N, Perera YR, Damo SM, Chazin WJ Protein Sci. 2026 Jan;35(1):e70399. doi: 10.1002/pro.70399. PMID:41427682[12] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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