In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding of large proteins or macromolecular protein complexes. There are a number of classes of molecular chaperones, all of which function to assist large proteins in proper protein folding during or after synthesis, and after partial denaturation. Chaperones are also involved in the translocation of proteins for proteolysis.
Peripheral membrane proteins, or extrinsic membrane proteins, are membrane proteins that adhere only temporarily to the biological membrane with which they are associated. These proteins attach to integral membrane proteins, or penetrate the peripheral regions of the lipid bilayer. The regulatory protein subunits of many ion channels and transmembrane receptors, for example, may be defined as peripheral membrane proteins. In contrast to integral membrane proteins, peripheral membrane proteins tend to collect in the water-soluble component, or fraction, of all the proteins extracted during a protein purification procedure. Proteins with GPI anchors are an exception to this rule and can have purification properties similar to those of integral membrane proteins.
Cryptobiosis or anabiosis is a metabolic state in extremophilic organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop, preventing reproduction, development, and repair. When environmental conditions return to being hospitable, the organism will return to its metabolic state of life as it was prior to cryptobiosis.
Cardiolipin is an important component of the inner mitochondrial membrane, where it constitutes about 20% of the total lipid composition. It can also be found in the membranes of most bacteria. The name "cardiolipin" is derived from the fact that it was first found in animal hearts. It was first isolated from the beef heart in the early 1940s by Mary C. Pangborn. In mammalian cells, but also in plant cells, cardiolipin (CL) is found almost exclusively in the inner mitochondrial membrane, where it is essential for the optimal function of numerous enzymes that are involved in mitochondrial energy metabolism.
Amyloid beta denotes peptides of 36–43 amino acids that are the main component of the amyloid plaques found in the brains of people with Alzheimer's disease. The peptides derive from the amyloid-beta precursor protein (APP), which is cleaved by beta secretase and gamma secretase to yield Aβ in a cholesterol-dependent process and substrate presentation. Aβ molecules can aggregate to form flexible soluble oligomers which may exist in several forms. It is now believed that certain misfolded oligomers can induce other Aβ molecules to also take the misfolded oligomeric form, leading to a chain reaction akin to a prion infection. The oligomers are toxic to nerve cells. The other protein implicated in Alzheimer's disease, tau protein, also forms such prion-like misfolded oligomers, and there is some evidence that misfolded Aβ can induce tau to misfold.
The mitochondrial permeability transition pore is a protein that is formed in the inner membrane of the mitochondria under certain pathological conditions such as traumatic brain injury and stroke. Opening allows increase in the permeability of the mitochondrial membranes to molecules of less than 1500 daltons in molecular weight. Induction of the permeability transition pore, mitochondrial membrane permeability transition, can lead to mitochondrial swelling and cell death through apoptosis or necrosis depending on the particular biological setting.
Phosphoenolpyruvate carboxykinase is an enzyme in the lyase family used in the metabolic pathway of gluconeogenesis. It converts oxaloacetate into phosphoenolpyruvate and carbon dioxide.
Innexins are transmembrane proteins that form gap junctions in invertebrates. Gap junctions are composed of membrane proteins that form a channel permeable to ions and small molecules connecting the cytoplasm of adjacent cells. Although gap junctions provide similar functions in all multicellular organisms, it was not known what proteins invertebrates used for this purpose until the late 1990s. While the connexin family of gap junction proteins was well-characterized in vertebrates, no homologues were found in non-chordates.
Phosphatidylethanolamine (PE) is a class of phospholipids found in biological membranes. They are synthesized by the addition of cytidine diphosphate-ethanolamine to diglycerides, releasing cytidine monophosphate. S-Adenosyl methionine can subsequently methylate the amine of phosphatidylethanolamines to yield phosphatidylcholines.
Adenine nucleotide translocator (ANT), also known as the ADP/ATP translocase (ANT), ADP/ATP carrier protein (AAC) or mitochondrial ADP/ATP carrier, exchanges free ATP with free ADP across the inner mitochondrial membrane. ANT is the most abundant protein in the inner mitochondrial membrane and belongs to mitochondrial carrier family.
Glutaredoxin 2 (GLRX2) is an enzyme that in humans encoded by the GLRX2 gene. GLRX2, also known as GRX2, is a glutaredoxin family protein and a thiol-disulfide oxidoreductase that maintains cellular thiol homeostasis. This gene consists of four exons and three introns, spanned 10 kilobase pairs, and localized to chromosome 1q31.2–31.3.
Voltage-dependent anion-selective channel 1 (VDAC-1) is a beta barrel protein that in humans is encoded by the VDAC1 gene located on chromosome 5. It forms an ion channel in the outer mitochondrial membrane (OMM) and also the outer cell membrane. In the OMM, it allows ATP to diffuse out of the mitochondria into the cytoplasm. In the cell membrane, it is involved in volume regulation. Within all eukaryotic cells, mitochondria are responsible for synthesis of ATP among other metabolite needed for cell survival. VDAC1 therefore allows for communication between the mitochondrion and the cell mediating the balance between cell metabolism and cell death. Besides metabolic permeation, VDAC1 also acts as a scaffold for proteins such as hexokinase that can in turn regulate metabolism.
ADP/ATP translocase 4 (ANT4) is an enzyme that in humans is encoded by the SLC25A31 gene on chromosome 4. This enzyme inhibits apoptosis by catalyzing ADP/ATP exchange across the mitochondrial membranes and regulating membrane potential. In particular, ANT4 is essential to spermatogenesis, as it imports ATP into sperm mitochondria to support their development and survival. Outside this role, the SLC25AC31 gene has not been implicated in any human disease.
Voltage-dependent anion-selective channel protein 2 is a protein that in humans is encoded by the VDAC2 gene on chromosome 10. This protein is a voltage-dependent anion channel and shares high structural homology with the other VDAC isoforms. VDACs are generally involved in the regulation of cell metabolism, mitochondrial apoptosis, and spermatogenesis. Additionally, VDAC2 participates in cardiac contractions and pulmonary circulation, which implicate it in cardiopulmonary diseases. VDAC2 also mediates immune response to infectious bursal disease (IBD).
Richard I. Morimoto is a Japanese American molecular biologist. He is the Bill and Gayle Cook Professor of Biology and Director of the Rice Institute for Biomedical Research at Northwestern University.
In membrane biology, fusion is the process by which two initially distinct lipid bilayers merge their hydrophobic cores, resulting in one interconnected structure. If this fusion proceeds completely through both leaflets of both bilayers, an aqueous bridge is formed and the internal contents of the two structures can mix. Alternatively, if only one leaflet from each bilayer is involved in the fusion process, the bilayers are said to be hemifused. In hemifusion, the lipid constituents of the outer leaflet of the two bilayers can mix, but the inner leaflets remain distinct. The aqueous contents enclosed by each bilayer also remain separated.
Dehydrin (DHN) is a multi-family of proteins present in plants that is produced in response to cold and drought stress. DHNs are hydrophilic, reliably thermostable, and disordered. They are stress proteins with a high number of charged amino acids that belong to the Group II Late Embryogenesis Abundant (LEA) family. DHNs are primarily found in the cytoplasm and nucleus but more recently, they have been found in other organelles, like mitochondria and chloroplasts.
Proteostasis is the dynamic regulation of a balanced, functional proteome. The proteostasis network includes competing and integrated biological pathways within cells that control the biogenesis, folding, trafficking, and degradation of proteins present within and outside the cell. Loss of proteostasis is central to understanding the cause of diseases associated with excessive protein misfolding and degradation leading to loss-of-function phenotypes, as well as aggregation-associated degenerative disorders. Therapeutic restoration of proteostasis may treat or resolve these pathologies.
Sugar transporter SWEET1, also known as RAG1-activating protein 1 and stromal cell protein (SCP), is a membrane protein that in humans is encoded by the SLC50A1 gene. SWEET1 is the sole transporter from the SLC50 (SWEET) gene family present in the genomes of most animal species, with the exception of the nematode Caenorhabditis elegans, which has seven.
Tardigrade specific proteins are types of intrinsically disordered proteins specific to tardigrades. These proteins help tardigrades survive desiccation, one of the adaptations which contribute to tardigrade's extremotolerant nature. Tardigrade specific proteins are strongly influenced by their environment, leading to adaptive malleability across a variety of extreme abiotic environments.
