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Lyn — Proto-Oncogene Tyrosine-Protein Kinase Lyn
Introduction
Lyn — Proto Oncogene Tyrosine Protein Kinase Lyn is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Overview
Lyn (Proto-Oncogene Tyrosine-Protein Kinase Lyn) is a Src family non-receptor tyrosine kinase with unique dual roles in both the immune system and nervous system. It is a 56 kDa protein encoded by the LYN gene on chromosome 8q13.1. Unlike other SFKs, Lyn is primarily expressed in hematopoietic cells (B lymphocytes, myeloid cells, mast cells) and in [microglia](/cell-types/microglia-neuroinflammation), where it serves as both a positive and negative regulator of immune signaling. In the nervous system, Lyn regulates microglial activation, neuroinflammation, and synaptic plasticity (Xu et al., 2012)[@xu2012]. title: Proto-Oncogene Tyrosine-Protein Kinase Lyn (Lyn) <div class="infobox infobox-protein">
| | | |---|---| | Protein Name | Proto-Oncogene Tyrosine-Protein Kinase Lyn | | Gene | [LYN](/proteins/lyn-protein) | | UniProt ID | [P07948](https://www.uniprot.org/uniprot/P07948) | | Molecular Weight | 56 kDa | | Subcellular Localization | Plasma membrane, Cytoplasm, Endosomes | | Protein Family | Src family non-receptor tyrosine kinases |
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Structure
Lyn shares the canonical Src family kinase architecture with some unique features:
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Lyn — Proto-Oncogene Tyrosine-Protein Kinase Lyn
Introduction
Lyn — Proto Oncogene Tyrosine Protein Kinase Lyn is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
Overview
Lyn (Proto-Oncogene Tyrosine-Protein Kinase Lyn) is a Src family non-receptor tyrosine kinase with unique dual roles in both the immune system and nervous system. It is a 56 kDa protein encoded by the LYN gene on chromosome 8q13.1. Unlike other SFKs, Lyn is primarily expressed in hematopoietic cells (B lymphocytes, myeloid cells, mast cells) and in [microglia](/cell-types/microglia-neuroinflammation), where it serves as both a positive and negative regulator of immune signaling. In the nervous system, Lyn regulates microglial activation, neuroinflammation, and synaptic plasticity (Xu et al., 2012)[@xu2012]. title: Proto-Oncogene Tyrosine-Protein Kinase Lyn (Lyn) <div class="infobox infobox-protein">
| | | |---|---| | Protein Name | Proto-Oncogene Tyrosine-Protein Kinase Lyn | | Gene | [LYN](/proteins/lyn-protein) | | UniProt ID | [P07948](https://www.uniprot.org/uniprot/P07948) | | Molecular Weight | 56 kDa | | Subcellular Localization | Plasma membrane, Cytoplasm, Endosomes | | Protein Family | Src family non-receptor tyrosine kinases |
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Structure
Lyn shares the canonical Src family kinase architecture with some unique features:
N-terminal myristoylation and palmitoylation: Dual lipid modification for membrane targeting, similar to Fyn
Unique domain (residues 1-65): Lyn-specific sequences that determine substrate specificity; contains binding sites for immune receptors
SH3 domain (residues 68-125): Binds proline-rich sequences; autoinhibitory function
Catalytic kinase domain (residues 240-490): ATP binding and phosphotransferase activity
C-terminal tail: Tyr508 (human) phosphorylation by CSK maintains autoinhibition
Lyn exists as two alternatively spliced isoforms: LynA (56 kDa, full-length) and LynB (53 kDa, lacking 21 amino acids in the unique domain), with potentially different signaling properties (Corey et al., 1998)[@corey1998].
Normal Function
Hematopoietic Cell Signaling
Lyn is the predominant SFK in B cells and myeloid cells:
B cell receptor (BCR) signaling: Phosphorylates ITAM motifs on Ig-α/Ig-β, initiating BCR signaling cascades
Negative regulation: Phosphorylates ITIM motifs on inhibitory receptors (CD22, FcγRIIB), recruiting SHIP-1 phosphatase to dampen signaling
Mast cell degranulation: Regulates FcεRI signaling and histamine release
Dendritic cell function: Modulates antigen presentation and cytokine production
Microglial Function
In the central nervous system, Lyn is highly expressed in microglia:
Toll-like receptor (TLR) signaling: Phosphorylates [TLR4](/entities/tlr4) and adaptor proteins, modulating inflammatory responses to bacterial LPS
[TREM2](/proteins/trem2-protein) signaling: May modulate [TREM2](/genes/trem2)-DAP12 signaling in microglia, affecting phagocytosis and inflammatory phenotypes
Fc receptor signaling: Regulates microglial response to antibody-opsonized material
Cytokine production: Controls production of TNF-α, IL-6, and other inflammatory mediators
Synaptic Function
Lower levels of Lyn are found in [neurons](/entities/neurons) where it modulates:
[NMDA](/entities/nmda-receptor) receptor function: Can phosphorylate NMDA receptor subunits, similar to Fyn
GABAergic transmission: Modulates GABA receptor function in some contexts
Synaptic plasticity: Contributes to [long-term potentiation](/mechanisms/long-term-potentiation) and depression
Role in Disease
Neurodegenerative Diseases
Lyn's role in neuroinflammation links it to multiple neurodegenerative conditions:
Isoform-selective targeting: Different effects of LynA vs LynB may be therapeutically relevant
Challenges
Dual functions: Lyn's both activating and inhibitory roles complicate therapeutic targeting
Peripheral immune effects: Systemic Lyn inhibition may impair normal immune function
[Blood-brain barrier](/entities/blood-brain-barrier): Need for CNS-penetrant compounds for neurodegeneration
Key Publications
Xu Y, Harder KW, Huntington ND, Hibbs ML. Lyn tyrosine kinase: accentuating the positive and the negative. Immunity. 2012;36(4):515-24. [doi:10.1016/j.immuni.2012.04.004](https://doi.org/10.1016/j.immuni.2012.04.004)
Corey SJ, Anderson SM. Src-related tyrosine protein kinases in hematopoiesis. Blood. 1999;93(1):1-14. PMID: 9864146(https://pubmed.ncbi.nlm.nih.gov/9864146/)
Hibbs ML, Harder KW, Armes J, et al. Sustained activation of Lyn tyrosine kinase in vivo leads to autoimmunity. J Exp Med. 2002;196(12):1593-604. [doi:10.1084/jem.20020715](https://doi.org/10.1084/jem.20020715)
[Cell Signaling: Lyn](https://www.cellsignal.com/) - Lyn pathway information
Background
The study of Lyn — Proto Oncogene Tyrosine Protein Kinase Lyn has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
References
[Xu Y, Harder KW, Huntington ND, Hibbs ML, Lyn tyrosine kinase: accentuating the positive and the negative (2012)](https://doi.org/10.1016/j.immuni.2012.04.004)
[Corey SJ, Dombroski-Ferlan PM, Zuo S, et al, Biochemical and functional comparisons of the Lyn and Abl protein tyrosine kinases (1998)](https://doi.org/10.1038/sj.onc.2003.0209)
[Scapini P, Pereira S, Zhang H, Lowell CA, Multiple roles of Lyn kinase in myeloid cell signaling and function (2009)](https://doi.org/10.1111/j.1600-065X.2008.00739.x)
[Henneke P, Takeuchi O, van Strijp JA, et al, Novel engagement of CD14 and multiple toll-like receptors by group B streptococci (2001)](https://doi.org/10.4049/jimmunol.167.12.7069)