KCa2.3 contains 6 transmembrane domains, a pore-forming region, and intracellular N- and C- termini[3][1] and is readily blocked by apamin. The gene for KCa2.3, KCNN3, is located on chromosome 1q21.
Tags: Integral membrane proteins, Ion channels, Membrane proteins, Proteins, Transmembrane proteins
SK3 is a small-conductance calcium-activated potassium channel partly responsible for the calcium-dependent after hyperpolarisation current (IAHP). It belongs to a family of channels known as small-conductance potassium channels, which consists of three members – SK1, SK2 and SK3 (KCNN1, 2 and 3 respectively), which share a 60-70% sequence identity.[1] These channels have acquired a number of alternative names, however a NC-IUPHAR has recently achieved consensus on the best names, KCa2.1 (SK1), KCa2.2 (SK2) and KCa2.3 (SK3).[2] Small conductance channels are responsible for the medium and possibly the slow components of the IAHP.
The SK channel family contains 4 members - SK1, SK2, SK3, and SK4.
Mutations in KCa2.3 are suspected to be a possible underlying cause for several neurological disorders, including schizophrenia, bipolar disorder, Alzheimer’s disease, anorexia nervosa and ataxia[6][7][8] as well as myotonic muscular dystrophy.
All SK channels can be pharmacologically blocked by quaternary ammonium salts of a plant-derived neurotoxin bicuculline.[6] In addition, SK channels(SK1-SK3) are sensitive to blockade by the bee venom apamin, [7] but SK4 (IK) is not. and the scorpion venom tamapin.[8]
KCa2.3 channels play a major role in human physiology, particularly in smooth muscle relaxation. The expression level of KCa2.3 channels in the endothelium influences arterial tone by setting arterial smooth muscle membrane potential. The sustained activity of KCa2.3 channels induces a sustained hyperpolarisation of the endothelial cell membrane potential, which is then carried to nearby smooth muscle through gap junctions.[5] Blocking the KCa2.3 channel or suppressing KCa2.3 expression causes a greatly increased tone in resistance arteries, producing an increase in peripheral resistance and blood pressure.
Shown on the right is the three dimensional structure of the Lysine 2,3-aminomutase protein. The structure was determined by X-ray crystallography to 2.1 Angstrom resolution and was seen to crystallize as a homotetramer.[2] KAM was first purified and characterized in Clostridium subterminale for studies of Lysine metabolism.
LSm proteins are characterized by a beta sheet (the secondary structure), folded into the LSm fold (the tertiary structure), polymerization into a six or seven member torus (the quaternary structure), and binding to RNA oligonucleotides.[7] A modern paradigm classifies proteins on the basis of protein structure and is a currently active field, with three major approaches, SCOP (Structural Classification of Proteins), CATH (Class, Architecture, Topology, Homologous superfamily), and FSSP/DALI (Families of Structually Similar Proteins).
Collagen structure is complex. Its conformation can be considered at the monomeric level (individual) collagen molecules and/or at its aggregate level, how the monomers are arranged i.e. their packing structure (fibrils, networks, etc. - see table below).
Human UCH-L1 and the closely related protein UCHL3 have the most complicated knot structure yet discovered for a protein, with five knot crossings. It is speculated that a knot structure may increase a protein's resistance to degradation in the proteasome.[3] [4]
Intrinsically unstructured proteins, often referred to as naturally unfolded proteins or disordered proteins, are proteins characterized by their lack of stable tertiary structure as isolated subunits. The discovery of intrinsically unfolded proteins challenged the traditional protein structure paradigm, which states that a specific well-defined structure was required for the correct function of a protein and that the structure defines the function of the protein. This is clearly not the case for intrinsically unfolded proteins that remain functional despite the lack of a well-defined structure.
Top7 is an artificial 93-amino acid protein, classified as a de novo protein since it was designed by Brian Kuhlman in David Baker's laboratory at the University of Washington and the Fred Hutchinson Cancer Research Center to have a unique fold not found in nature.[1] The protein was designed ab initio on a computer with the help of protein structure prediction algorithms. X-ray crystallography on the protein after it was made, revealed that the structure was indeed very similar (1.2 Å RMSD) to the computer predicted structure. The structure consists of two alpha helices and two beta sheets.
The legume lectins are also interesting from the point of view of protein structure. Despite the conserved structure of the legume lectin subunit, they can adopt a wide range of quaternary structures [5]. The reason behind this remarkable variability is to be found in the interaction with multivalent ligands.
RI is the classic leucine-rich repeat protein, consisting of alternating ?-helices and ?-strands along its backbone. These secondary structure elements wrap around in a curved, right-handed solenoid that resembles a horseshoe. The parallel ?-strands and ?-helices form the inner and outer wall of the horseshoe, respectively. The structure appears to be stabilized by buried asparagines at the base of each turn, as it passes from ?-helix to ?-strand. The ?? repeats alternate between 28 and 29 residues in length, effectively forming a 57-residue unit that corresponds to its genetic structure (each exon codes for a 57-residue unit).
"A structure that lies outside the plasma membrane and surrounds the entire cell."
N- Acetylserotonin O-methyltransferase is an enzyme that is coded for by genes located on the PAR region of the X and Y chromosome, and is most abundantly found in the pineal gland and retina of humans. [2] Although the exact structure of N- Acetylserotonin O-methyltransferase has yet to be determined by X-Ray diffraction, the crystal structure of the Maf domain of human N- Acetylserotonin O-methyltransferase-like protein has been found