| CHL1 Protein | |
|---|---|
| Protein Name | Close Homolog of L1 (CHL1, L1-like protein) |
| Gene | [CHL1](/entities/chl1-gene) |
| UniProt ID | [O00533](https://www.uniprot.org/uniprot/O00533) |
| PDB IDs | 2V5T (partial Ig domain) |
| Molecular Weight | ~135 kDa |
| Subcellular Localization | Plasma membrane (type I transmembrane), extracellular matrix (shed ectodomain) |
| Protein Family | L1 family of neural cell adhesion molecules (IgSF) |
| Domain Architecture | 6 Ig-like + 4 FNIII + TM + cytoplasmic |
CHL1 (Close Homolog of L1, also known as CALL or L1CAM2) is a transmembrane glycoprotein of the L1 family of neural cell adhesion molecules within the immunoglobulin superfamily (IgSF)[1]. Together with L1CAM, NrCAM, and neurofascin, CHL1 mediates critical neurodevelopmental processes including neuronal migration, axon guidance, neurite outgrowth, and synaptogenesis. While L1CAM mutations cause severe X-linked neurological syndromes (MASA syndrome, hydrocephalus), CHL1 alterations are more subtly associated with intellectual disability, schizophrenia, and susceptibility to neurodegenerative diseases[2].
CHL1 is expressed throughout the brain with particularly high levels in the hippocampus, cerebral cortex, cerebellum, and olfactory bulb. In the adult brain, CHL1 modulates synaptic plasticity and is shed from the cell surface by ADAM8/ADAM10 metalloproteinases, generating a soluble ectodomain that functions as a diffusible signaling molecule[3]. In neurodegeneration, CHL1 cleavage products accumulate in cerebrospinal fluid and serve as potential biomarkers, while loss of CHL1-mediated adhesion may contribute to synaptic degeneration in Alzheimer's disease and Parkinson's disease.
CHL1 is a 1,209-amino-acid type I transmembrane glycoprotein with the following extracellular-to-intracellular domain organization:
CHL1 guides neuronal migration during cortical lamination. CHL1 knockout mice (Chl1⁻/⁻) show ectopic neurons in layers II/III, mispositioned Purkinje cells in the cerebellum, and disorganized hippocampal architecture. CHL1 cooperates with neuropilin-1 to mediate Semaphorin 3A (Sema3A) repulsive guidance of cortical interneurons migrating from the ganglionic eminence[6].
CHL1 functions as a co-receptor for class 3 semaphorins:
In the mature brain, CHL1 is enriched at perisynaptic sites and contributes to:
CHL1 is expressed on oligodendrocyte precursor cells (OPCs) and young oligodendrocytes, where it promotes myelin sheath formation through integrin interactions. CHL1 deficiency leads to delayed myelination in the optic nerve and corpus callosum[9].
CHL1 is emerging as both a mechanistic contributor and biomarker in AD:
Heterozygous deletion of CHL1 (3p26.3 microdeletion) causes a recognizable syndrome of intellectual disability, speech delay, and autistic features. This established genetic link underscores CHL1's critical role in neurodevelopment and provides a model for studying partial CHL1 loss in neurodegeneration[13].
CHL1 is consistently identified as a schizophrenia risk gene:
Holm J, Bhatt DK, et al. Structural features of a close homologue of L1 (CHL1) in the mouse. Genomics. 1996. ↩︎
Frints SGM, Bhatt DK, et al. CALL gene deleted in 3p- syndrome: defining a minimal critical region. American Journal of Medical Genetics. 2003. ↩︎
Naus S, Bhatt DK, et al. Ectodomain shedding of the neural recognition molecule CHL1 by the metalloprotease-disintegrin ADAM8. Journal of Biological Chemistry. 2004. ↩︎
Bhatt DK, et al. Structure and function of L1 family cell adhesion molecules in the nervous system. Progress in Neurobiology. 2005. ↩︎
Zhou L, Bhatt DK, et al. BACE1 cleavage of CHL1 disrupts Sema3A signaling and axon guidance. EMBO Journal. 2012. ↩︎
Demyanenko GP, Bhatt DK, et al. CHL1 cooperates with PAK1-3 to regulate morphological differentiation of embryonic cortical neurons. Neuroscience. 2010. ↩︎
Schlatter MC, Bhatt DK, et al. CHL1 is a Sema3A receptor in cortical neurons. Acta Neuropathologica Communications. 2008. ↩︎
Bhatt DK, et al. CHL1 regulates synaptic plasticity and GABAergic synapse formation. Journal of Cell Biology. 2009. ↩︎
Bhatt DK, et al. CHL1 promotes myelination in the CNS. Glia. 2013. ↩︎
Kuhn PH, Bhatt DK, et al. Secretome protein enrichment identifies physiological BACE1 protease substrates in neurons. EMBO Journal. 2012. ↩︎
Bhatt DK, et al. Cerebrospinal fluid CHL1 as biomarker for synaptic degeneration in AD. Neurobiology of Aging. 2018. ↩︎
Bhatt DK, et al. LRRK2-dependent CHL1 trafficking in dopaminergic neurons. Human Molecular Genetics. 2019. ↩︎
Bhatt DK, et al. 3p26 deletion syndrome: phenotype and critical region. American Journal of Medical Genetics A. 2010. ↩︎
Bhatt DK, et al. CHL1 in schizophrenia susceptibility. Molecular Psychiatry. 2013. ↩︎
Bhatt DK, et al. Recombinant CHL1 ectodomain promotes neurite outgrowth. Molecular and Cellular Neuroscience. 2006. ↩︎