Functioning gene. 21.00 kb; 37 Exons.

7097.00 bp; Number of transcripts: 1; Type: Messenger.
Two alternatively truncated spliced variant, coding secreted proteins (lacking the part of the extracellular domains).

No.

2135 Amino acids (AA). Plexins are receptors for axon molecular guidance molecules semaphorins. Plexin signalling is important in pathfinding and patterning of both neurons and developing blood vessels. Plexin-B1 is a surface cell receptor. When it binds to its ligand SEMA4D it activates several pathways by binding of cytoplasmic ligands, like RHOA activation and subsequent changes of the actin cytoskeleton, axon guidance, invasive growth and cell migration.
It monomers and heterodimers with PLXNB2 after proteolytic processing. Binds RAC1 that has been activated by GTP binding.
It binds PLXNA1 and by similarity ARHGEF11, ARHGEF12, ERBB2, MET, MST1R, RND1, NRP1 and NRP2.
This family features the C-terminal regions of various plexins. The cytoplasmic region, which has been called a SEX domain in some members of this family is involved in downstream signalling pathways, by interaction with proteins such as Rac1, RhoD, Rnd1 and other plexins.
Three copies of a cysteine rich repeat are found in Plexin. The function of the repeat is unknown.

It is highly expressed in fetal kidney, digestive system (from esophagus to colon), thyroid, prostate and trachea and at slightly lower levels in fetal brain, lung, female reproductive system (breast, uterus and ovary) and liver.

Three isoforms have been identified: The isoform 1 is located in cell membrane and the isoforms 2 and 3 are secreted proteins.

Plexin B1 has several molecular functions, like a receptor activity, transmembrane receptor activity, protein binding, semaphorin receptor and semaphorin receptor binding. It is implicated in the next biological processes: Signal transduction, intracellular signalling cascade, multicellular organismal development, cell migration and positive regulation of axonogenesis.

It belongs to the plexin family and it contains 3 IPT/TIG domains and one Sema domain.

Wong et al. (2007) identified 13 different somatic mutations in the cytoplasmic domain of the PLXNB1 gene in prostate cancer tissue. Mutations were found in 8 (89%) of 9 prostate cancer bone metastases, in 7 (41%) of 17 lymph node metastases, and in 41 (46%) of 89 primary cancers. Forty percent of prostate cancers contained the same mutation, and the majority of the primary tumors showed overexpression of the plexin-B1 protein. In vitro functional expression studies of the 3 most common mutations showed that the mutant proteins resulted in increased cell motility, invasion, adhesion, and lamellipodia extension compared to wildtype. The mutations acted by hindering RAC1 and RRAS binding and GTP activity.