The main function of crystallins at least in the lens of the eye is probably to increase the refractive index while not obstructing light. However, this is not their only function. It is becoming increasingly clear that crystallins may have a several metabolic and regulatory functions, both within the lens and in other parts of the body [5].
Tags: Proteins
In biology, a crystallin is a water-soluble structural protein found in the lens of the eye, accounting for the transparency of the structure. It has also been identified in other places such as the heart [1] and aggressive breast cancer tumors [2]. Since it has been shown that lens injury may promote nerve regeneration[3], crystallin has been an area of neural research. So far, it has been demonstrated that crystallin ? b2 (crybb2) may be a neurite promoting factor [4].
sHsps have some structural features in common: Very characteristic is a homologous and highly conserved amino acid sequence, the so-called ?-crystallin-domain at the C-terminus. These sequences consist of 80 to 100 residues with a homology between 20% and 60% and form ?-sheets, which are important for the formation of stable dimers.[1][2] The N-terminus consists of a less conserved region, the so-called WD/EPF domain, followed by a short variable sequence with a rather conservative site near the C-terminus of this domain. The C-terminal part of the sHsps consists of the above mentioned ?-crystallin domain, followed by a variable sequence with high motility
sHsps have some structural features in common: Very characteristic is a homologous and highly conserved amino acid sequence, the so-called ?-crystallin-domain at the C-terminus. These sequences consist of 80 to 100 residues with a homology between 20% and 60% and form ?-sheets, which are important for the formation of stable dimers.[1][2] The N-terminus consists of a less conserved region, the so-called WD/EPF domain, followed by a short variable sequence with a rather conservative site near the C-terminus of this domain. The C-terminal part of the sHsps consists of the above mentioned ?-crystallin domain, followed by a variable sequence with high motility
Crystallins from a vertebrate eye lens are classified into three types: alpha, beta and gamma crystallins. These distinctions are based on the order in which they elute from a gel filtration chromatography column. These are also called ubiquitous crystallins. Beta- and gamma-crystallins are similar in sequence, structure and domains topology, and thus have been grouped together as a protein superfamily called ??-Crystallins. The ?-crystallin superfamily and ??-crystallins compose the major superfamily of proteins present in the crystalline lens. In addition to these crystallins there are other taxon-specific crystallins which are only found in the lens of some organisms; these include delta,
Interestingly and perhaps excitingly from an evolutionary perspective, some crystallins are active enzymes, while others lack activity but show homology to other enzymes.[6][7] The crystallins of different groups of organisms are related to a large number of different proteins, with those from birds and reptiles related to lactate dehydrogenase and argininosuccinate lyase, those of mammals to alcohol dehydrogenase and quinone reductase, and those of cephalopods to glutathione S-transferase and aldehyde dehydrogenase. Whether these crystallins are products of a happy accident of evolution, in that these particular enzymes happened to be transparent and highly-soluble, or whether these diverse enzymatic activities are
Hsp27 is a chaperone of the sHsp (small heat shock protein) group among ubiquitin, ?-crystallin, Hsp20 and others. The common functions of sHsps are chaperone activity, thermotolerance, inhibition of apoptosis, regulation of cell development, and cell differentiation. They also take part in signal transduction.
Hsp27 is a chaperone of the sHsp (small heat shock protein) group among ubiquitin, ?-crystallin, Hsp20 and others. The common functions of sHsps are chaperone activity, thermotolerance, inhibition of apoptosis, regulation of cell development, and cell differentiation. They also take part in signal transduction.
The protein has no known natural ligand[2] and its function is unclear. It is suspected that it acts as a calcium channel in the cell membran
SAP97 is expressed throughout the body in epithelial cells, including the kidney and brain[1]. There is some evidence that SAP97 regulates cell-to-cell adhesion during cell death, and may interact with HPV. In the brain, SAP97's function is involved in the trafficking of transmembrane receptors from the ER to the plasma membrane[2]. SAP97's function has been investigated by reducing its expression by knockout or increasing its expression heterologously. Mice in which the SAP97 gene has been knocked out die perinatally, have a cleft palate, and deficiencies in renal function.[3][4] Overexpression of SAP97 in mammalian neurons leads to increased synaptic strength. [5]
ER-? may have anti-proliferative effects and therefore oppose the actions of ER-? in reproductive tissue.[4] ER-? may also have an important role in adpative function of the lung during pregnancy.[5]
There is a vast array of studies investingating the function of "membrane channels", these frequently combine the patch clamp technique with pharmacology. The process by which membrane channel function is altered by drugs and biochemicals is termed "channel modulation". Functional channelomic studies also includes study of diseases resulting from their mis-function. Such a disease is termed a channelopathy.
The precise function of the prion protein is not known, but there is substantial evidence that it serves as a copper-dependent antioxidant.[
The function of sphingomyelin remained unclear until recently when it was found to have a function in signal transduction. The plasma membrane of cells is highly enriched in sphingomyelin and is considered largely to be found in the exoplasmic leaflet of the cell membrane. However, there is some evidence that there may also be a sphingomyelin pool in the inner leaflet of the membrane [1] [2]. Moreover, neutral sphingomyelinase-2 - an enzyme that breaks down sphingomyelin into ceramide has been found to localise exclusively to the inner leaflet further suggesting that there may be sphingomyelin present there.
SNARE proteins are the key components of the molecular machinery that drives fusion of membranes in exocytosis. Their function however is subject to fine tuning by various regulatory protein collectively referred to as SNARE masters.
Centrin is required for duplication of centrioles.[2] It may also play a role in severing of microtubules by causing calcium-mediated contraction.[3] The majority of centrin in the cell is non-centrosomal whose function is not yet clear.[4]