KLHL36

Last updated

KLHL36
Identifiers
Aliases KLHL36 , C16orf44, kelch like family member 36
External IDs MGI: 2385305; HomoloGene: 32598; GeneCards: KLHL36; OMA:KLHL36 - orthologs
Orthologs
SpeciesHumanMouse
Entrez
Ensembl
UniProt
RefSeq (mRNA)

NM_001303451
NM_024731

NM_146219

RefSeq (protein)

NP_001290380
NP_079007

NP_666331

Location (UCSC) Chr 16: 84.65 – 84.67 Mb Chr 8: 120.59 – 120.6 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

Kelch-Like Protein 36 (abbreviated KLHL36) is a protein that in humans is encoded by the KLHL36 gene. [5] Although the gene's specific function has yet to be characterized, it is predicted to serve as a substrate adaptor for Cullin-RING E3 ubiquitin ligase (CRL3) complexes, contributing to proteostasis. [6]

Contents

Gene

In humans, the KLHL 36 gene consists of 5 exons and 4 introns spanning 19,176 base pairs on the positive strand of chromosome 16 (16q24.1). [5]

The gene is a member of the Kelch-like gene family, which is characterized by a conserved BTB-BACK-Kelch domain architecture. Kelch-like genes encode proteins that recognize and bind specific protein substrates, bind the scaffold protein cullin 3 in the CRL3 complex, and pass the substrate protein to the complex to facilitate ubiquitylation and degradation at the proteasome. [6]

Figure 1. KLHL36 location on Chromosome 16 in Homo sapiens. KLHL36 is surrounded by two protein coding genes, USP10 downstream on the positive strand, and COTL1 upstream on the negative strand. KLHL36 Locus, Genome.png
Figure 1. KLHL36 location on Chromosome 16 in Homo sapiens. KLHL36 is surrounded by two protein coding genes, USP10 downstream on the positive strand, and COTL1 upstream on the negative strand.

Homology

Orthologs

The KLHL36 gene is highly conserved in vertebrates. Orthologs of KLHL36 are present in jawed vertebrates tracing back to cartilaginous fishes, although no orthologs have been identified in jawless vertebrates or invertebrates. [7] This suggests that the KLHL36 gene originated in a common ancestor of jawed vertebrates roughly 462 millions years ago. [8]

KLHL is remarkably conserved across jawed vertebrates, sharing a greater than 77 percent sequence identity with many species of cartilaginous fishes, whose lineages diverged from that of humans roughly 462 million years ago. KLHL36 orthologs are summarized in Table 1.

Table 1. Divergence of Selected Orthologs of Human KLHL36
Genus and speciesCommon nameTaxonomic groupMedian Date of Divergence (Millions of Years ago)Accession #Sequence length (aa)Sequence identity to human protein (%)Sequence similarity to human protein (%)
Homo sapiens Humans Hominidae 0NP_079007.2616100100
Pan paniscus BonoboHominidae6.4XP_054956502.161699.8100
Nasalis larvatus Proboscis Monkey Primata 28.8KAL4835633.161699.299.7
Mus musculus House Mouse Rodentia 87NP_666331.161385.792.2
Canis lupus familiaris Domestic Dog Carnivora 94XP_005620696.261696.898.5
Physeter macrocephalus Sperm Whale Artiodactyla 94XP_023980819.161696.197.7
Notamacropus eugenii Tamar Wallaby Marsupialia 160XP_072492309.161589.894.6
Ornithorhynchus anatinus Platypus Monotremata 180XP_001509771.261687.292.9
Gallus gallus Red Junglefowl Aves 319XP_040537292.161585.492
Dermochelys coriacea Leatherback Sea Turtle Reptilia 319XP_038224216.161585.192.4
Alligator sinensis Chinese AlligatorReptilia319XP_006022804.161585.192.5
Geotrypetes seraphini Gaboon Caecilian Amphibia 352XP_033796775.161580.489.3
Eleutherodactylus coqui Common CoquiAmphibia352XP_066439605.161572.483.8
Ambystoma mexicanum AxolotlAmphibia352XP_069492346.161572.985.6
Latimeria chalumnae West Indian Ocean Coelacanth Sarcopterygii 415XP_069492346.161478.787.5
Thalassophryne amazonicaAmazon Toadfish Actinopterygii 429XP_034031579.161156.470.7
Danio rerio ZebrafishActinopterygii429NP_001018416.36106174.6
Hypanus sabinusAtlantic Stingray Chondrychthytes 462XP_059849157.161277.886.9
Callorhinchus miliiAustralian GhostsharkChondrychthytes462XP_042196266.161578.285.8
Scyliorhinus caniculaSmall Spotted CatsharkChondrychthytes462XP_038662242.161277.385.9
Figure 2. KLHL36 Corrected number of amino acid changes over evolutionary history. Cytochrome c represents a highly conserved control, and Fibrinogen alpha represents a poorly conserved control. KLHL36 divergence graph.png
Figure 2. KLHL36 Corrected number of amino acid changes over evolutionary history. Cytochrome c represents a highly conserved control, and Fibrinogen alpha represents a poorly conserved control.

Among the 20 selected orthologs, the amino acid identity at a given position was conserved in all orthologs at 35.4% of positions.

Figure 2 shows the divergence of KLHL36 in terms of corrected number of amino acid changes over millions of years. KLHL36 is remarkably highly conserved, similar to cytochrome c, with minimal changes in amino acid composition over time. [9] [10] Corrected amino acid changes are calculated as 100 * ln(1 - (M/100)), where M represents the observed number of amino acid changes per hundred amino acids in selected orthologs of KLHL36.

Paralogs

54 paralogs of KLHL36 have been identified, with its closest relatives being KLHL13 and KLHL26. [11] The KLHL family of genes contains 42 genes from KLHL1 to KLHL42. Paralogs of KLHL36 are summarized in Table 2.

Table 2. Identity and Similarity of KLHL36 Most Closely Related Relatives
Gene/Paralog (Isoform)Sequence Length (Amino Acids)Query CoveragePercent Identity MatchPercent Similarity MatchNumber of IsoformsAccession Number
KLHL36 (1)6161001001003NP_079007.2
KLHL13 (e)6049438607NP_001161775.2
KLHL26 (3)6049436556NP_001332911.1
KLHL32 (n)55684345115NP_001310192.1
KLHL226349633519NP_116164.2
KLHL316349332521NP_001003760.2
KLHL146289131512NP_116164.2
KLHL346449429451NP_695002.1
KLHL185748829471NP_079286.2
KLHL156048929471NP_085127.2
KLHL2 (1)5938928495NP_009177.3
KLHL 3 (2)5559028493NP_001244123.1
KEAP1 6249328431NP_036421.2
KLHL176429327466NP_938073.1
KLHL1 (1)7488327444NP_065917.1
KLHL12 (1)6069227439NP_001289980.
KLHL10 (1)6089227432NP_001316524.1
KLHL28 (1)5859127426NP_001295041.
KLHL25 5899427421NP_071925.2

Expression

Figure 3. Graph of KLHL36 Expression Across Tissues. RPKM, or reads per kilobase per million reads, is a normalized measure of gene expression from RNA sequencing. KLHL36 expression graph.png
Figure 3. Graph of KLHL36 Expression Across Tissues. RPKM, or reads per kilobase per million reads, is a normalized measure of gene expression from RNA sequencing.

KLHL36 is expressed ubiquitously at moderate levels across all tissues, with moderate variation across tissues. [5] The highest expression of the protein is observed in the testes, fat, and thyroid. [12]

Whole body transcriptomic tissue analyses have revealed that, while KLHL36 is expressed at its highest absolute values in the testes, fat, and thyroid, it is expressed at its highest levels relative to other proteins in cells of the immune system, such as B cells, T cells, and monocytes. [13]

Transcript

There are 6 known transcript variants of KLHL36, the most common transcript variant being transcript variant 1. Transcript variant 1 encodes the longest and most common isoform, isoform 1. [5] Transcript variant 1 is 7,559 nucleotides in length and contains 5 exons. [5] Its 5' untranslated region is 158 nucleotides in length and its 3' untranslated region is 5556 nucleotides in length.

Transcript Variants X1 and X2 contain the same coding sequence and encode an identical protein to transcript variant 1, with slightly differing 5' untranslated regions. Transcript Variant 2 encodes a slightly different protein product, missing part of the internal amino acid sequence but with the Kelch motifs at the C terminal intact. Transcript Variant X4 is significantly truncated, missing a large portion of the coding sequence and the 3' UTR and containing no Kelch motifs. Transcript Variants of KLHL36 and their corresponding protein isoforms are summarized in Table 3. [5]

Table 3. Homo sapiens KLHL36 Transcript Variants and Corresponding Protein Isoforms
Transcript VariantAccession NumberLength (Nucleotides)Exon CountCorresponding Protein IsoformAccession NumberAmino Acid Length
Transcript Variant 1NM_024731.475595Protein Isoform 1NP_079007.2616
Transcript Variant X1XM_047434648.175475Protein Isoform X1XP_047290604.1616
Transcript Variant X2XM_005256149.375035Protein Isoform X1XP_005256206.1616
Transcript Variant X3XM_047434649.177975Protein Isoform X1XP_047290605.1616
Transcript Variant 2NM_001303451.273704Protein Isoform 2NP_001290380.1553
Transcript Variant X4XM_047434650.113804Protein Isoform X2XP_047290606.1372

Many RNA binding proteins are predicted to bind to the 5' UTR KLHL36 Transcript Variant 1 mRNA, including YBX1, Vts1, RBM4, KHSRP, and RBMX. [14] Several additional RNA binding proteins are predicted to bind to the 3' UTR, including YBX1, PUM2, EIF4B, MBNL2, ACO1, KHSRP, RBMY1A1, SFRS13A, YTHDC1, ELAVL1, FUS, ZRANB2, PABPC1, and SFRS9. [14] RNA binding proteins that are predicted to bind the promoter of KLHL36 include ZNF667, ZNF530, ZIC4, SNF257, TFAP2A, TFAP2C, ZTBT24, KLF10, KLF12, SREBF1, KLF5, ZVED4, and NFYB. [14]

Figure 4 consists of a conceptual translation of KLHL36 Transcript Variant 1 coding sequence, which demonstrates the layout of the mRNA and the corresponding amino acids, protein domains, and exon boundaries. [5]

Figure 4a. Conceptual Translation of KLHL36 Transcript Variant 1 mRNA, including BTB/POZ domain, BACK domain, Kelch Motifs, start and stop codons, and exon boundaries. KLHL36 conceptual translation a.png
Figure 4a. Conceptual Translation of KLHL36 Transcript Variant 1 mRNA, including BTB/POZ domain, BACK domain, Kelch Motifs, start and stop codons, and exon boundaries.
Figure 4b. Conceptual Translation of KLHL36 Transcript Variant 1 mRNA, including 3' UTR, polyA signal sequences, and major polyadenylation sites. KLHL36 conceptual translation b.png
Figure 4b. Conceptual Translation of KLHL36 Transcript Variant 1 mRNA, including 3' UTR, polyA signal sequences, and major polyadenylation sites.

Protein

Figure 3. AlphaFold v4 predicted tertiary structure of Homo sapiens KLHL36 protein isoform 1. KLHL36 protein structure.png
Figure 3. AlphaFold v4 predicted tertiary structure of Homo sapiens KLHL36 protein isoform 1.

There are 3 protein isoforms of KLHL36, the most common and longest being isoform 1. [5] Isoform 1 is a kelch-like protein that is 616 amino acids in length with a molecular mass of roughly 70 kilodaltons and an isoelectric point of 5.5. [16] The charge of the protein in a neutral environment is -12, with no charge clusters identified. [17]

The protein contains a BTB/POZ domain of 135 amino acids at its N-terminus, which is predicted to mediate homodimerization and be involved in cullin 3 binding. [6] [18] At its C-terminus, the protein contains 6 Kelch-motif domains which form a β-propeller that is predicted to be involved in substrate binding. [19] [20]

There are no unusually scarce or common amino acids present in KLHL36. [17] The secondary structure of the protein is dominated by alpha helices towards the N-terminus in the region of the BTB/POZ Domain and the BACK domain, and by beta sheets towards the C-terminus in the β-propeller domain. [21]

Immunofluorescence staining of KLHL36 in the A-549 cell line suggests that the protein localizes to the cytoplasm. [22] DeepLoc-2.0 analysis of KLHL36 supports this finding, calculating its highest likelihood of subcellular localization to be the cytoplasm at 0.70, followed by the nucleus at 0.48 and the lysosome at 0.25. [23] Analysis of KLHL36's primary structure reveals no signal peptide, no transmembrane domains, no mitochondrial targeting, no nuclear localization sequence, and no tracking motifs. [17]

PhosPhoSite Plus and DTU Health Tech Bioinformatic Services predict many post-translational modifications of KLHL36, including phosphorylation, ubiquitylation, and acetylation. [24] [25] These modifications likely contribute to regulating the function of KLHL36 by inducing conformational changes and regulating KLHL36 abundance through ubiquitylation and subsequent proteasomal degradation.

Protein Interactions

Cullin 3 has been shown to directly bind multiple BTB domains through a conserved amino terminal domain. [26] It is likely that cullin 3 binds the BTB domain present at the N-terminal of KLHL36 to mediate ubiquitylation and degradation of substrate proteins bound by KLHL36. It is not currently known what proteins KLHL36 might bind to facilitate their degradation.

STRING Functional Protein Association Database identifies 10 proteins with which KLHL36 is predicted to interact. These proteins are summarized in Table 4. [27]

Table 4. STRING Predicted Interaction Partners of Homo sapiens KLHL36
ProteinFull NameBasis for InteractionStatistical Significance of BasisSubcellular LocalizationBrief Protein Overview
CUL3Cullin 3Co-Expression, Experimental Data, Co-Mentioned in Abstracts0.049, 0.428, 0.058Cytoplasm, nucleoplasm, microtubules, cytokinetic bridge Component of cullin-RING-based BCR E3 ubiquitin-protein ligase complexes, which mediate ubiquitylation and proteasomal degradation of target proteins.
DCLK2Serine/threonine-protein kinase, doublecortin like kinase 2Experimental Data, Co-Mentioned in Abstracts0.091, 0.581Cytoplasm, microtubulesPart of CaMK protein kinase family that is thought to have reduced affinity and dependence for Ca2+ and CAM compared to other members of the CaMK family.
CXorf56STING1 ER exit protein 1Experimental Data0.46Nucleoplasm, centrosomeUncharacterized
PACRGParkin coregulated gene proteinExperimental Data0.568 Mitochondria, cilia, flagella Supresses cell death induced by accumulation of unfolded Pael receptor.
APEX1Apurinic/apyrimidinic endodeoxyribonuclease 1Experimental Data0.479Nucleoplasm, centrosomeMultifunctional protein thought to play a central role in cellular response to oxidative stress, involved in DNA repair and redox regulation of transcription.
KIAA0513Uncharacterized protein KIAA0513Co-Expression, Co-Mentioned in Abstracts0.138, 0.522CytosolUncharacterized
FAM92B/CIBAR2CBY1 interacting BAR domain containing 2Co-Expression, Co-Mentioned in Abstracts0.049, 0.448CytoplasmMay play a role in ciliogenesis, cooperates with CBY1 to recruit endosomal vesicles at distal appendages during ciliogenesis.
CEP104 Centrosomal protein of 104 kDaCo-Expression0.457Centrosome, cytoplasmRequired for ciliogenesis and structural integrity at ciliary tip.
TMEM127Transmembrane protein 127Co-Expression0.451N/ANegative regulator of TOR signaling pathway that controls cell proliferation, tumor suppressing.
SLC15A5 Solute carrier family 15 member 5Co-Mentioned in Abstracts0.571N/AProton oligopeptide cotransporter

Clinical Significance

UniProt identifies 770 variants of the KLHL36 gene, with 94 marked as "pathogenic" or "likely pathogenic". [11] A single nucleotide polymorphism downstram of KLHL36 (rs12716755) has been reported as a risk variant for early onset Alzheimer's disease. [28] A genome-wide association study (GWAS) reported an aggregation of 134 single nucleotide polymorphisms implicated in psychological resilience and stress-related psychiatric outcomes in the region of KLHL36 on chromosome 16. [29]

Additionally, transcriptomic analyses have revealed disease-associated changes in KLHL36 expression. KLHL36 mRNA levels have been shown to be lower in gastrointestinal tumors, and increased expression is correlated with positive prognoses in pancreatic cancer and cholangiocarcinoma. [30] Additionally, elevated KLHL36 levels have been associated with reduced tumor proliferation in pancreatic adenocarcinoma models, suggesting a possible tumor suppressor role. [31] Analyses of triple-negative breast cancer tumors have found that KLHL36 expression can be induced by TNFα stimulation, and that induction of expression can be reversed by the flavonoid apigenin. [32]

KLHL36 has also been implicated in psychiatric contexts. In rodent models, antidepressant treatment and exercise have been negatively correlated with expression of KLHL36 in the brain. [33] One sequencing analysis found that levels of KLHL36 were significantly increased in both individuals affected by seasonal affective disorder and suicidal ideation. [34]

References

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