OR5L2

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Overview

OR5L2 (Olfactory Receptor Family 5 Subfamily L Member 2) is a protein that in humans is encoded by the OR5L2 gene. It produces a seven-transmembrane G-protein-coupled receptor (GCPR) involved in signal transduction. This receptor is thought to help initiate the neuronal responses that underlie odor perception.

Gene

OR5L2, also known as OR11-153, is a gene in Homo sapiens (Accession: NM_001004739.1) located in cytogenetic band 11q12.1, spanning 936 base pairs (55,827,219-55,828,154 GRCh38/hg38 assembly) and encodes a 331 amino acid protein...

The olfactory receptor gene family is the largest in the genome, with the OR5L2 gene situated within a dense cluster of olfactory receptor genes on chromosome 11. It is plus-strand oriented in the 5′ to 3′ direction relative to the reference sequence. Neighboring genes upstream of OR5L2 consist of OR5L1, OR5D18, while OR5D16 and the OR9M1P pseudogene are located downstream.

OR5L2 is a single-exon, intronless gene, similar to its OR counterparts, with the entire coding sequence being transcribed into one continuous RNA. Due to the absence of introns, no alternative splicing takes place, nor are there any known isoforms.

Protein

The OR5L2 protein (Accession: NP_001004739.1) belongs to the olfactory receptor subfamily OR5L, which are Class A (rhodopsin-like) G-protein-coupled receptors with seven transmembrane domains. OR5L2 has a predicted molecular weight of ~35kDa and an isoelectric point of ~8.5 pI.

The protein consists of 331 residues, with a composition dominated by hydrophobic amino acids characteristic of a seven-transmembrane olfactory GPCR. Leucine, valine, isoleucine, phenylalanine, and methionine together account for over 40% of the sequence, reflecting the membrane-embedded helices. Polar and charged residues are comparatively scarce, with basic residues (K and R) at 7.1% and acidic residues (E and D) at 5.5%, consistent with short cytosolic and extracellular loops rather than large soluble domains.

In comparison to other proteins, OR5L2 is markedly more hydrophobic, with over 40% hydrophobic residues–typical for olfactory receptors but far above the proteome average. It also completely lacks tryptophan, an uncommon feature in human proteins and consistent with olfactory receptors’ reliance on other aromatic residues for transmembrane packing.

Moreover, there is a conserved “NPL…Y” motif in all orthologs located within transmembrane domain 7, a region critical for maintaining the structural integrity of GCPRs and stabilizing the conformational changes required for receptor activation.

Protein Regulation

Post-Translational Modification

There is a N-X-S/T consensus motif in OR5L2’s extracellular N-terminus, hinting at a possible functional post-translational glycosylation site. Functionally, this modification may affect folding and stability, trafficking to the plasma membrane, and ligand binding. This N-X-S/T site at positions 5-8 is preserved across orthologous species–including mammals, birds, reptiles, and amphibians.

All other predicted sites, phosphorylation motifs for protein kinase C (PKC) and Casein kinase 2 (CK2) are positioned on residues that are either within or overlap with the transmembrane helix regions. This likely results in the sites being relatively unused, due to lacking access by ER lumen machinery.

Sub-Cellular Localization

OR5L2 receives highest predictions for being localized within the endoplasmic reticulum (ER) and plasma membrane, with smaller votes for vacuolar, Golgi, and mitochondrial compartments. Moreover, no nuclear-localization tools were able to detect cleavable signal peptide sites at the N-terminus, which is expected since GPCRs use their first transmembrane helix as a signal anchor for ER insertion.

Homology

Orthologs

In vertebrates, olfactory receptor (OR) genes are highly conserved and display significant sequence similarity as they are “phylogenetically derived from nine common ancestor genes”. OR5L2 is conserved in mammals, birds, reptiles, and amphibians but absent in fish and invertebrates, suggesting it evolved with terrestrial olfaction.

Table 1: Orthologs of OR5L2 in Homo sapiens. Sorted first by estimated date of divergence, then by sequence identity to human protein. Color coordinated by species type. OR5L2 is found in terrestrial organisms, disappears in bony fish.

Paralogs

OR5L2 has multiple paralogs, but Table 2 highlights those with the highest sequence similarity. The presence of OR5L2 in amphibians, coupled with its absence in earlier aquatic lineages where only OR5L1 is retained, indicates that OR5L2 likely originated from a duplication of OR5L1. This duplication appears to coincide with the evolutionary transition from fully aquatic to semi-terrestrial life, suggesting that OR5L2 emerged as part of the sensory diversification associated with early terrestrial adaptation.

Table 2: Paralogs of OR5L2 in Homo sapiens. Sorted by sequence identity to human OR5L2 protein.

Evolutionary History

Figure 3: Corrected sequence divergence of OR5L2 in Homo sapiens compared to orthologous sequences.

OR5L2 first appeared in evolutionary history in the late Devonian Period (about 419.2 million and 358.9 million years ago), when the “first four-legged amphibians appeared, indicating the colonization of land by vertebrates”. This olfactory superfamily consists of “390 putatively functional genes and 465 pseudogenes arranged into 18 gene families and 300 subfamilies”

Protein Divergence

OR5L2 shows moderate divergence across species. In the comparative plot, its trendline falls between cytochrome c (highly conserved) and fibrinogen alpha (highly divergent), indicating an intermediate rate of evolutionary change (Figure 3).

Interacting Proteins

OR5L2 is predicted to interact with several proteins involved in GPCR signaling. Key partners include β-arrestins (ARRB1, ARRB2), which regulate receptor desensitization and internalization, and GRK2, a kinase that phosphorylates activated receptors. Heterotrimeric G-protein subunits (GNAL, GNB1, GNG7, GNG13) and cAMP-dependent kinases (PRKACA, PRKACB, PRKACG) are also predicted interactors, highlighting roles in olfactory signal transduction, phosphorylation, and intracellular trafficking. Predicted interacting proteins of OR5L2, identified through PSICQUIC and STRING analyses, are summarized in Table 3.

File:Tabletwo.png

Table 3: Predicted protein interactors of OR5L2 in Homo sapiens.

Clinical Significance

Disease Association

Although OR5L2 is classically defined as an olfactory receptor, emerging data indicate broader functional relevance. In the central nervous system (CNS), OR5L2 transcripts are highly expressed in the human amygdala, with levels altered across Alzheimer’s disease, Parkinson’s disease, Creutzfeldt–Jakob disease, and schizophrenia, suggesting a potential role in neural regulatory processes beyond olfaction

Outside the nervous system, OR5L2 is dysregulated in hepatocellular carcinoma (HCC) and appears as a highly connected node within lncRNA-mRNA coexpression networks, implying possible involvement in tumor-associated regulatory pathways. Somatic variants such as p.E207K have been identified in adenocarcinoma samples at varying allele frequencies, though COSMIC currently classifies these mutations as neutral passenger events. OR5L2 has also been reported in non-small cell lung cancers that develop resistance to crizotinib, raising the possibility that alterations in this receptor may contribute to drug-resistance mechanisms through GPCR-linked signaling.

Overall, while OR5L2 is not considered a canonical driver gene, its dysregulated expression and recurrent mutations across multiple tissues suggest potential value as a biomarker or modulator of disease-associated pathways.

References

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