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Cyclic Nucleotide-Gated Channels (CNG1-4) Antibodies
The cyclic nucleotides cAMP and cGMP are important intracellular messengers involved in a wide variety of signal transduction events such as the visual transduction, relaxation of smooth muscles, intestinal secretion of water and salt, reabsorption of Na+ and water in the distal tubule of the nephrons. cAMP/cGMP activate Ca2+ -permeable ion channels called cyclic nucleotide-gated channels (CNG or CNC). Activation of CNG channels leads to depolarization of the membrane voltage and to a concomitant increase of the cytosolic Ca2+. CNG mediate response to light in retinal rods and cones. CNGs have also been found in a variety of other non-sensory tissues where they might fulfill various physiological functions. CNG consists of two distinct subunits, designated a and b subunits. Several CNG alpha-subunits (CNGa 1-3) & beta subunits (subunit 2 or CNGb1-2 or CNG4-5) and numerous isoforms (e.g. CNGb1a and CNGb1b in rods and OSN) have been cloned from various species. a-subunit can form functional channel when expressed alone in heterologous expression system. In contrast, b-subunits do not form functional channel by themselves but can modulate the channel property of a-subunits. CNG display a protein topology similar to the voltage-gated K+-Channels: Intracellular N and C-termini, 6 transmembrane domains or segments (S1-S6). The region between S5 and S6 contains the ion-conducting pore (P). The cyclic nucleotide-binding region is found at the c-terminus. Native functional CNG channels may exists as heteromultimer containing some combination of a, and b subunits. Bovine CNG1 was initially cloned and characterized from rod cells. CNG1 (rat 683 aa, mouse 684, human 686 aa; also describes as OCNC1) is primarily expressed in outer segment of photoreceptor rod cells in retina and inner medulla of kidney. In rat, CNG1 is expressed in a wide variety of tissues (eye, pineal gland, pituitary, adrenal, spleen, brain, heart, skeletal muscle, and testis). Human/mouse CNG1 exhibit ~88% sequence homology. CNG2 or OCNC1 (rat/mouse/rabbit 664 aa, bovine 663 aa) is primarily expressed in olfactory sensory neurons. It is ~80% homologous with CNG1. Unlike CNG1, CNG2 is activated both by cAMP and cGMP. Another cGMP-gated channel called CNG3 (mouse 537 aa, rat 611 aa, human, 694 aa, bovine 706 aa, chicken 645 aa) has been cloned from heart, kidney, testis, sperm, and taste buds. CNG3, localized on the pore side of taste buds in the circumvallate papillae, termed CNGgust is probably rat homolog of human cone CNG3 (~82% identity). Deletion of CNG3 gene in mice leads of degeneration of cone photoreceptors suggesting its important role in retinal functions. CNG beta-subunit or subunit 2 (also called CNG4) have been cloned from the rod outer segments (hRCNC2a and hRCNC2b) and from olfactory neurons (rOCNC2, also called CNG5). Human RCNC2a (623 aa; missing 1-286 aa) and RCNC2b (909 aa) are alternatively splice and only differ in their N-terminus. The two b proteins show ~30% identity with human a CNG1. Additional alternatively spliced CNG4D (missing 522-530 aa) and CNG4E (missing 515-532 aa) are also expressed. CNG b-subunits do not form functional channel but can form heterooligomeric complex with CNG1-3. The olfactory b-subunit is expressed throughout the nasal epithelium, especially in olfactory sensory neurons, and in the vomeronasal organ. ADI has produced highly specific rabbit antibodies to
various CNGs using peptide sequences specific to each protein.
m=mouse; r=rat; h=human; b=bovine; d=dog; ~CT
or ~NT=near C or N-terminus. EC=Extracellular; CP=Cytoplasmic
domain; Control peptides (unconjugated, free, antigenic
peptides), because of their small size, are not recommended
for Western. They should be used in ELISA/antibody blocking
studies. |
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