FAM13B

Family with sequence similarity 13 member B is a protein which in humans is encoded by the FAM13B gene,^[5] also known as C5ORF5. The FAM13B gene is found in vertebrates and jawed fish. FAM13B is expressed ubiquitously in human tissues^[6] and has been linked to maglinant myelomas^[7] susceptibility to atrial fibrillation, a cardiac arrhythmia.^[8]

Human Chromosome 5

FAM13B
Identifiers
Aliases	FAM13B, ARHGAP49, C5orf5, FAM13B1, KHCHP, N61, family with sequence similarity 13 member B
External IDs	OMIM: 609371; MGI: 2447834; HomoloGene: 9585; GeneCards: FAM13B; OMA:FAM13B - orthologs
Gene location (Human) Chr. Chromosome 5 (human)[1] Band 5q31.2 Start 137,937,960 bp[1] End 138,051,961 bp[1]
Gene location (Mouse) Chr. Chromosome 18 (mouse)[2] Band 18|18 B1 Start 34,575,404 bp[2] End 34,639,884 bp[2]
RNA expression pattern Bgee Human Mouse (ortholog) Top expressed in Achilles tendon germinal epithelium tail of epididymis palpebral conjunctiva seminal vesicula Brodmann area 23 parietal pleura sural nerve visceral pleura endothelial cell Top expressed in tail of embryo substantia nigra facial motor nucleus motor neuron genital tubercle lateral hypothalamus paraventricular nucleus of hypothalamus dorsomedial hypothalamic nucleus ventral tegmental area medullary collecting duct More reference expression data BioGPS n/a
Gene ontology Molecular function GTPase activator activity Cellular component cytosol Biological process positive regulation of GTPase activity regulation of small GTPase mediated signal transduction signal transduction Sources:Amigo / QuickGO
Orthologs Species Human Mouse Entrez 51306 225358 Ensembl ENSG00000031003 ENSMUSG00000036501 UniProt Q9NYF5 Q8K2H3 RefSeq (mRNA) NM_001101800 NM_001101801 NM_016603 NM_146084 RefSeq (protein) NP_001095270 NP_001095271 NP_057687 NP_666196 Location (UCSC) Chr 5: 137.94 – 138.05 Mb Chr 18: 34.58 – 34.64 Mb PubMed search [3] [4]
Wikidata
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Tertiary Structure of the human FAM13B protein from AlphaFold

Molecular Features

Gene

The FAM13B gene is located on human chromosome 5q31, spanning 5610 base pairs and containing 23 exons.^[6]

mRNA

There are 18 transcript variants, the longest mRNA contains 5610 base pairs.^[6]

Expression

The FAM13B gene is expressed at high levels ubiquitously among human cell tissues with some variability, with the highest expression in the brain and the lowest expression in the liver.^[6]

Protein

The longest protein product of FAM13B consists of 915 amino acids^[9] with a molecular mass of 105kD.^[10] FAM13B variants have the potential to encode several swapped proteins, including proteins with internal deletions, with different C termini, and with a deletion of the N terminus.^[10] The protein has an isoelectric point of 4.9.^[11] The human FAM13B protein is localized in the nucleoplasm and contains multiple peroxisomal targeting signals and nuclear localization signals.^[12] The FAM13B protein has a lower amount of threonine and a higher amount of glutamate compared to other human proteins.^[11]

The FAM13B contains 2 disordered region and 2 conserved domains:^[6]

• RHO GTPase-activating proteins domain (RhoGAP) - crucial in cell cytoskeletal organization, growth, differentiation, neuronal development and synaptic functions.^[13]
• N-terminal homeodomain-like domain of metazoan RecQ protein-like 4 (RecQL4_SLD2_NTD) - involved in various cellular process, including DNA replication, recombination, and repair.^[14]

The RHOGAP domain is also found in the orthologs.

Annotated FAM13B protein, made from The CUCKOO Workgroup

Post-translation modifications

The human FAM13B protein can undergo post-translational modifications including phosphorylation, acetylation, and methylation.^[12]

Annotated post-translational modification sites on human FAM13B protein, made from The CUCKOO Workgroup

Interacting proteins

The human FAM13B protein interacts with several proteins that are localized in the nucleoplasm, including RAC1, NME5, SPATA24, HIGD1A, PPP2CA, SAMHD1, UNK, YWHAZ.^[15]

Evolution

Multiple sequence alignment of a conserved area of the FAM13B protein

Orthologs

Orthologs of the FAM13B gene can be found in vertebrates including mammals, aves, reptiles, amphibians, and jawed fish.^[6] There are no FAM13B orthologs found in invertebrates. FAM13B is more conserved in mammals, aves, and reptiles. FAM13B has a moderate mutation rate that is slower than Fibrinogen Alpha Chain but faster than Cytochrome C.

Table of selected orthologs from all animal groups

Genus and Species	Common Name	Estimated Divergence (MYA)	Accession Number	Amino Acid Length	Sequence Similarity (%)
Homo sapiens	Humans	0	NP_001372850	915	100
Macaca mulatta	Rhesus monkey	28.8	NP_001247877	916	99.2
Mus musculus	House mouse	87	NP_666196	851	87.3
Alligator sinesis	Chinese alligator	319	XP_006026918	930	87.0
Gallus gallus	Chicken	319	NP_001264674	905	85.9
Xenopus tropicalis	Tropical clawed frog	352	XP_002933679	831	72.0
Amblyraja radiata	Thorny skate	462	XP_032885277	825	58.4

Paralogs

The human FAM13B gene has two paralogs, FAM13A^[16] and FAM13C.^[17] Similar to FAM13B, the FAM13A and FAM13C are found in vertebrates including mammals, aves, reptiles, amphibians, and jawed fish. The paralogs are not found in invertebrates.

Clinical significance

FAM13B is frequently deleted in malignant myelomas, suggesting its potential role in cancer development.^[7] Altered expression of FAM13B has been linked to susceptibility to atrial fibrillation,^[7] a cardiac arrhythmia.^[8]