FAM13B

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

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

mRNA
There are 18 transcript variants, the longest mRNA contains 5610 base pairs.

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.

Protein
The longest protein product of FAM13B consists of 915 amino acids with a molecular mass of 105kD. 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. The protein has an isoelectric point of 4.9. The human FAM13B protein is localized in the nucleoplasm and contains multiple peroxisomal targeting signals and nuclear localization signals. The FAM13B protein has a lower amount of threonine and a higher amount of glutamate compared to other human proteins.

The FAM13B contains 2 disordered region and 2 conserved domains:


 * RHO GTPase-activating proteins domain (RhoGAP) - crucial in cell cytoskeletal organization, growth, differentiation, neuronal development and synaptic functions.
 * 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.

The RHOGAP domain is also found in the orthologs.

Post-translation modifications
The human FAM13B protein can undergo post-translational modifications including phosphorylation, acetylation, and methylation.

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.

Orthologs
Orthologs of the FAM13B gene can be found in vertebrates including mammals, aves, reptiles, amphibians, and jawed fish. 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.

Paralogs
The human FAM13B gene has two paralogs, FAM13A and FAM13C. 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. Altered expression of FAM13B has been linked to susceptibility to atrial fibrillation, a cardiac arrhythmia.