{"type": "root", "children": [{"type": "p", "children": [{"type": "t", "text": "\nHuman complement component C8 is an essential part of the membrane attack complex (MAC) formed by the sequential assembly of complement proteins. C8 is an oligomeric protein consisting of a disulfide‐linked C8α–γ heterodimer and a noncovalently associated C8β subunit. Uniquely, C8γ belongs to the lipocalin family and exhibits a barrel‐like fold with a calyx typically used for accommodating small hydrophobic ligands. Structural studies have shown that C8γ interacts with specific regions of C8α—such as the MACPF domain and a characteristic insertion segment—inducing conformational changes that facilitate subsequent protein–protein interactions vital for MAC assembly. Detailed glycoproteomics and mass spectrometry analyses have also revealed post‐translational modifications on C8γ (including N‐glycosylation, C‐mannosylation, and even low‐abundance O‐glycosylation) that might influence its stability and function in the MAC structure."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "1", "end_ref": "5"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nFunctional investigations have demonstrated that although C8γ is not absolutely required for complement-mediated lysis of Gram-negative bacteria, it enhances the efficiency of MAC-induced cytolysis and supports proper complex assembly. Crystallographic analyses and binding experiments using lauric acid as a pseudoligand have revealed that the lipocalin calyx of C8γ—divided into a hydrophilic opening and a large hydrophobic cavity—can undergo conformational changes, particularly through the movement of key tyrosine residues (Y83 and Y131) that act as a dynamic gate. Complementary mutagenesis and molecular dynamics simulations further underscore the importance of disulfide linkage and loop regions in C8γ for its bonding with C8α, suggesting that these structural features may regulate ligand access and fine-tune MAC function."}, {"type": "fg", "children": [{"type": "fg_fs", "start_ref": "6", "end_ref": "8"}]}, {"type": "t", "text": "\n"}]}, {"type": "t", "text": "\n\n"}, {"type": "p", "children": [{"type": "t", "text": "\nBeyond its molecular role in complement activation, recent clinical research has identified a potential association between C8γ and neurocognitive outcomes. Elevated levels of C8γ in astrocyte-derived exosomes have been observed in patients with obstructive sleep apnea who exhibit mild cognitive impairment, suggesting that C8γ might serve as a biomarker and possibly influence neuroinflammatory or neurodegenerative processes. These findings provide a basis for further exploration into the multifaceted functions of C8γ, linking its structural and regulatory roles within the complement system to broader implications in human disease."}, {"type": "fg", "children": [{"type": "fg_f", "ref": "9"}]}, {"type": "t", "text": "\n"}]}, {"type": "rg", "children": [{"type": "r", "ref": 1, "children": [{"type": "t", "text": "Daniel J Slade, Leslie L Lovelace, Maksymilian Chruszcz, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Crystal structure of the MACPF domain of human complement protein C8 alpha in complex with the C8 gamma subunit."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Mol Biol (2008)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.jmb.2008.03.061"}], "href": "https://doi.org/10.1016/j.jmb.2008.03.061"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "18440555"}], "href": "https://pubmed.ncbi.nlm.nih.gov/18440555"}]}, {"type": "r", "ref": 2, "children": [{"type": "t", "text": "Chasta L Parker, James M Sodetz "}, {"type": "b", "children": [{"type": "t", "text": "Role of the human C8 subunits in complement-mediated bacterial killing: evidence that C8 gamma is not essential."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Mol Immunol (2002)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/s0161-5890(02)00121-9"}], "href": "https://doi.org/10.1016/s0161-5890(02"}, {"type": "t", "text": "00121-9) PMID: "}, {"type": "a", "children": [{"type": "t", "text": "12413696"}], "href": "https://pubmed.ncbi.nlm.nih.gov/12413696"}]}, {"type": "r", "ref": 3, "children": [{"type": "t", "text": "Daniel J Slade, Brian Chiswell, James M Sodetz "}, {"type": "b", "children": [{"type": "t", "text": "Functional studies of the MACPF domain of human complement protein C8alpha reveal sites for simultaneous binding of C8beta, C8gamma, and C9."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biochemistry (2006)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1021/bi0601860"}], "href": "https://doi.org/10.1021/bi0601860"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "16618117"}], "href": "https://pubmed.ncbi.nlm.nih.gov/16618117"}]}, {"type": "r", "ref": 4, "children": [{"type": "t", "text": "Vojtech Franc, Jing Zhu, Albert J R Heck "}, {"type": "b", "children": [{"type": "t", "text": "Comprehensive Proteoform Characterization of Plasma Complement Component C8αβγ by Hybrid Mass Spectrometry Approaches."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Am Soc Mass Spectrom (2018)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1007/s13361-018-1901-6"}], "href": "https://doi.org/10.1007/s13361-018-1901-6"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "29532326"}], "href": "https://pubmed.ncbi.nlm.nih.gov/29532326"}]}, {"type": "r", "ref": 5, "children": [{"type": "t", "text": "Primrose Musingarimi, Mnason E Plumb, James M Sodetz "}, {"type": "b", "children": [{"type": "t", "text": "Interaction between the C8 alpha-gamma and C8 beta subunits of human complement C8: role of the C8 beta N-terminal thrombospondin type 1 module and membrane attack complex/perforin domain."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biochemistry (2002)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1021/bi026207h"}], "href": "https://doi.org/10.1021/bi026207h"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "12220191"}], "href": "https://pubmed.ncbi.nlm.nih.gov/12220191"}]}, {"type": "r", "ref": 6, "children": [{"type": "t", "text": "Brian Chiswell, Leslie L Lovelace, Charity Brannen, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Structural features of the ligand binding site on human complement protein C8gamma: a member of the lipocalin family."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biochim Biophys Acta (2007)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.bbapap.2007.03.004"}], "href": "https://doi.org/10.1016/j.bbapap.2007.03.004"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "17452033"}], "href": "https://pubmed.ncbi.nlm.nih.gov/17452033"}]}, {"type": "r", "ref": 7, "children": [{"type": "t", "text": "Athanassios Stavrakoudis "}, {"type": "b", "children": [{"type": "t", "text": "A disulfide linked model of the complement protein C8gamma complexed with C8alpha indel peptide."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "J Mol Model (2009)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1007/s00894-008-0412-y"}], "href": "https://doi.org/10.1007/s00894-008-0412-y"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "19048311"}], "href": "https://pubmed.ncbi.nlm.nih.gov/19048311"}]}, {"type": "r", "ref": 8, "children": [{"type": "t", "text": "Brian Chiswell, Daniel J Slade, James M Sodetz "}, {"type": "b", "children": [{"type": "t", "text": "Binding of the lipocalin C8gamma to human complement protein C8alpha is mediated by loops located at the entrance to the C8gamma ligand binding site."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Biochim Biophys Acta (2006)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.bbapap.2006.07.003"}], "href": "https://doi.org/10.1016/j.bbapap.2006.07.003"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "16935577"}], "href": "https://pubmed.ncbi.nlm.nih.gov/16935577"}]}, {"type": "r", "ref": 9, "children": [{"type": "t", "text": "Yanyan Yang, Tengqun Shen, Mengfan Li, et al. "}, {"type": "b", "children": [{"type": "t", "text": "Elevated complement component 8 gamma levels in astrocyte-derived exosomes are associated with cognitive impairment in obstructive sleep apnea patients without dementia."}]}, {"type": "t", "text": " "}, {"type": "i", "children": [{"type": "t", "text": "Neurosci Lett (2023)"}]}, {"type": "t", "text": " DOI: "}, {"type": "a", "children": [{"type": "t", "text": "10.1016/j.neulet.2022.137010"}], "href": "https://doi.org/10.1016/j.neulet.2022.137010"}, {"type": "t", "text": " PMID: "}, {"type": "a", "children": [{"type": "t", "text": "36509166"}], "href": "https://pubmed.ncbi.nlm.nih.gov/36509166"}]}]}]}