BFAR

BFAR Full Name

bifunctional apoptosis regulator

BFAR Introduction

BFAR, also known as bifunctional apoptosis regulator or RNF47, is a multi-domain protein that inhibits apoptosis by interfering with both the death receptor pathway and the mitochondrial pathway of programmed cell death. The human BFAR gene is located on chromosome 16p13.3, and encodes a protein of approximately fifty kilodaltons. BFAR is a member of the RING finger protein family, characterized by a zinc-coordinating RING domain at its C-terminus that confers E3 ubiquitin ligase activity, as well as a SAM domain that mediates protein-protein interactions. BFAR is widely expressed in human tissues, with the highest levels detected in the brain, heart, kidney, and testis, and lower expression in the liver, lung, and spleen. Within the cell, BFAR localizes to the cytoplasm and to the endoplasmic reticulum membrane, where it interacts with components of the apoptotic machinery. Through its dual domains, BFAR suppresses apoptosis by two distinct mechanisms: it binds to and inhibits caspase-8 at the death receptor complex, and it regulates the expression of BCL2 family proteins at the mitochondria.

Figure 1. Schematic structure of BFAR.

Molecular Structure and Domain Functions
BFAR contains three distinct functional domains: an N-terminal hydrophobic domain that anchors the protein to the endoplasmic reticulum membrane, a central SAM domain that mediates protein-protein interactions, and a C-terminal RING domain that confers E3 ubiquitin ligase activity. The SAM domain, or sterile alpha motif domain, is a conserved protein interaction module that promotes homo- and hetero-oligomerization. In BFAR, the SAM domain is required for binding to caspase-8, the initiator caspase of the death receptor pathway. By binding to caspase-8, BFAR prevents the recruitment and activation of caspase-8 at the death-inducing signaling complex, thereby blocking the extrinsic pathway of apoptosis. The RING domain coordinates two zinc ions through conserved cysteine and histidine residues, forming a cross-braced structure that is characteristic of RING E3 ligases. BFAR functions as an E3 ubiquitin ligase that catalyzes the transfer of ubiquitin from an E2 ubiquitin-conjugating enzyme to specific substrate proteins. One well-characterized substrate of BFAR is the pro-apoptotic BCL2 family protein BIM, which is ubiquitinated by BFAR and targeted for proteasomal degradation.

Role in Inhibiting the Death Receptor Pathway
The death receptor pathway of apoptosis is triggered by the binding of death ligands such as Fas ligand, tumor necrosis factor, and TRAIL to their cognate death receptors on the cell surface. Ligand binding induces receptor trimerization and the recruitment of the adaptor protein FADD and procaspase-8, forming the death-inducing signaling complex. At this complex, procaspase-8 is activated through proximity-induced autoproteolysis, releasing active caspase-8 into the cytoplasm where it triggers a cascade of downstream caspases leading to cell death. BFAR interacts with caspase-8 through its SAM domain and prevents the activation of caspase-8 at the death-inducing signaling complex. The mechanism of inhibition is not fully understood, but BFAR may sterically hinder the dimerization or autoproteolysis of procaspase-8, or it may recruit other proteins that inhibit caspase-8 activation.

Alternate Names for BFAR

BFAR; bifunctional apoptosis regulator; BAR; RNF47; RING finger protein 47; bifunctional apoptosis inhibitor;