Antibodies

Autophagy is important for the removal of damaged organelles or proteins as well as for the regulation of cellular homeostasis in response to stress. Proteins or organelles that are targeted for degradation are engulfed in a double-membrane structure called the autophagosome that eventually fuses with the lysosome to mediate cargo degradation. Atg5 plays an important regulatory role in the early steps of this process.

During times of cellular stress overloading of the protein folding machinery leads to the accumulation of incorrectly folded proteins. This triggers the unfolded protein response (UPR) in order to try to reestablish homeostasis or, if this fails, to induce apoptosis. The UPR pathway is mediated by a group of ER-associated transmembrane receptors including activating transcription factor 6 (ATF6). The presence of misfolded proteins is monitored by BiP, an Hsp70 family member.

Scavenger receptors play important roles in homeostasis and innate immunity by binding to endogenous and foreign molecules. Scavenger receptors on the plasma membrane of macrophages bind to ligand and allow their internalization and can also mediate pro- or anti-inflammatory signaling. The plasma membrane glycoprotein CD163 is a member of the scavenger receptor cysteine-rich (SRCR) protein family. CD163 contains nine SRCR domains and is expressed in macrophages and monocytes where it plays a role in innate immunity and regulation of inflammation in response to ligand binding.

Autophagy is an essential cellular process that maintains homeostasis through the degradation and recycling of cytoplasmic organelles and macromolecules. Substrates targeted for autophagy are engulfed in a double-membrane structure called the autophagosome which is then targeted to the lysosome for degradation. The initiation of autophagy requires two separate ubiquitin-like protein (UBL) systems that regulate autophagosome assembly. In these systems Atg7 acts as an E1-like enzyme for the UBLs Atg12 and Atg8.

During autophagy ubiquitinated cargo or substrates are engulfed in a double-membrane autophagosome and transported to the lysosome for degradation. This process is important for maintaining cellular homeostasis and for degrading damaged organelles or misfolded protein aggregates. p62, also known as sequestosome 1 (SQSTM1), is an autophagy receptor that recognizes and recruits cargo to the autophagosome through its interaction with Atg8.

Heat shock cognate 71 kDa protein (Hsc70), also known as HSPA8, is a member of the heat shock protein 70 family (Hsp70). Unlike Hsp70, it is a constitutively expressed chaperone protein and is involved in diverse cellular processes including protein folding and protein degradation. Hsc70 consists of two domains: the nucleotide binding domain (NBD) and the substrate binding domain (SBD). Hsc70, with the help of accessory proteins, exerts its chaperone activity by binding to short hydrophobic stretches of nascent or unfolded polypeptides through the SBD in an ATP-dependent manner.

Human leukocyte antigen G (HLA G) is a major histocompatibility complex (MHC) class I molecule that is primarily expressed in the placenta and is essential for the immune tolerance of the fetus during pregnancy. Unlike many HLA genes, HLA G has relatively few variants and is alternatively spliced into seven different isoforms. Of these isoforms four are membrane-bound while three are predicted to be soluble. Both the membrane-bound and soluble form of HLA G can induce immune tolerance by binding to inhibitory receptors on various immune cells including macrophages and monocytes.

Atg12 is a ubiquitin-like protein that plays an essential role in cellular homeostasis by regulating the degradation and recycling of cytoplasmic organelles and macromolecules. Atg12 is one of two ubiquitin-like protein systems that is required during the early steps of autophagosome formation. Upon the initiation of phagopore assembly Atg12 is activated by binding to the E1-like enzyme Atg7 and is then transferred to the E2 enzyme Atg10.

Cluster of differentiation 74 (CD74) is an important integral membrane protein that serves as a chaperone for MHC class II molecules. CD74, also known as the invariant chain or Ii, is needed for the proper folding and trafficking of MHC class II in antigen presenting cells. CD74 serves as a scaffold for MHC class II assembly. During assembly CD74 blocks the peptide binding cleft of MHC class II to prevent binding of antigenic peptides.

Mucin 1 (Muc1) is a heavily glycosylated protein that coats mucosal epithelial cells of the lungs, intestines, and other organs. Muc1 is thought to protect cells by binding to pathogens and responding to infections. During trafficking to the plasma membrane Muc1 is proteolytically cleaved in the endoplasmic reticulum to form a stable heterodimeric complex of two fragments. The smaller C-terminal region contains the cytoplasmic tail and transmembrane domain and is non-covalently bound to the larger glycosylated extracellular domain.