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Third Transmembrane Domain (third + transmembrane_domain)

Distribution by Scientific Domains

Life Sciences	80%

Selected Abstracts

Molecular prenatal diagnosis in a case of an X-linked dominant chondrodysplasia punctata

PRENATAL DIAGNOSIS, Issue 9 2003
N. V. Whittock
Abstract X-linked dominant chondrodysplasia punctata, (CDPX2,MIM302960) also known as Conradi,Hünermann,Happle syndrome, is a rare form of skeletal dysplasia that affects the skeleton, skin, hair, and eyes. The disorder is caused by mutations within the emopamil binding protein (Ebp) that functions as a delta(8), delta(7) sterol isomerase in the cholesterol biosynthesis pathway. To date, over 40 separate mutations have been reported in the Ebp gene, EBP, with no obvious correlation between the molecular defects and the severity of the clinical phenotype. We have studied a 30-year-old woman who presented in adulthood with skin, hair, and mild skeletal defects but no ocular abnormalities and have identified a heterozygous missense mutation within the third transmembrane domain of the protein. In addition, we have performed molecular prenatal testing on her unborn fetus. The results demonstrate inter-familial variability for missense mutations within the emopamil binding protein and add to the molecular data for CDPX2. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A conserved cysteine residue in the third transmembrane domain is essential for homomeric 5-HT3 receptor function

THE JOURNAL OF PHYSIOLOGY, Issue 4 2010
Dai-Fei Wu
The cysteine (Cys) residue at position 312 in the third transmembrane domain (M3) is conserved among 5-hydroxytryptamine type 3 (5-HT3) receptor subunits and many other subunits of the nicotinic acetylcholine (nACh) related Cys-loop receptor family, including most of the ,-aminobutyric acid type A (GABAA) and glycine receptor subunits. To elucidate a possible role for the Cys-312 in human 5-HT3A receptors, we replaced it with alanine and expressed the 5-HT3A(C312A) mutant in HEK293 cells. The mutation resulted in an absence of 5-HT-induced whole-cell current without reducing homopentamer formation, surface expression or 5-HT binding. The 5-HT3A(C312A) mutant, when co-expressed with the wild-type 5-HT3A subunit, did not affect functional expression of receptors, suggesting that the mutant is not dominant negative. Interestingly, co-expression of 5-HT3A(C312A) with 5-HT3B led to surface expression of heteropentamers that mediated small 5-HT responses. This suggests that the Cys-312 is essential for homomeric but not heteromeric receptor gating. To further investigate the relationship between residue 312 and gating we replaced it with amino acids located at the equivalent position within other Cys-loop subunits that are either capable or incapable of forming functional homopentamers. Replacement of 5-HT3A Cys-312 by Gly or Leu (equivalent residues in the nACh receptor , and , subunits) abolished and severely attenuated function, respectively, whereas replacement by Thr or Ser (equivalent residues in nACh receptor ,7 and GABAA, subunits) supported robust function. Thus, 5-HT3A residue 312 and equivalent polar residues in the M3 of other Cys-loop subunits are essential determinants of homopentameric gating. [source]

The ,1 and ,6 subunit subtypes of the mammalian GABAA receptor confer distinct channel gating kinetics

THE JOURNAL OF PHYSIOLOGY, Issue 2 2004
Janet L. Fisher
The GABAA receptors show a large degree of structural heterogeneity, with seven different subunit families, and 16 different subtypes in mammalian species. The , family is the largest, with six different subtypes. The ,1 and ,6 subtypes are among the most diverse within this family and confer distinct pharmacological properties to recombinant and neuronal receptors. To determine whether different single channel and macroscopic kinetic properties were also associated with these subtypes, the ,1 or ,6 subunit was expressed in mammalian cells along with ,3 and ,2L subunits and the kinetic properties examined with outside-out patch recordings. The ,1,3,2L receptors responded to GABA with long-duration openings organized into multi-opening bursts. In contrast, channel openings of the ,6,3,2L receptors were predominately short in duration and occurred as isolated, single openings. The subunit subtype also affected the deactivation rate of the receptor, which was almost 2-fold slower for ,6,3,2L, compared with the ,1,3,2L isoform. Onset of fast desensitization did not differ between the isoforms. To determine the structural domains responsible for these differences in kinetic properties, we constructed six chimeric subunits, combining different regions of the ,1 and ,6 subunits. The properties of the chimeric subunits indicated that structures within the third transmembrane domain (TM3) and the TM3,TM4 intracellular loop conferred differences in single channel gating kinetics that subsequently affected the deactivation rate and GABA EC50. The effect of agonist concentration on the rise time of the current showed that the extracellular N-terminal domain was largely responsible for binding characteristics, while the transmembrane domains determined the activation rate at saturating GABA concentrations. This suggests that subunit structures outside of the agonist binding and pore-lining domains are responsible for the kinetic differences conferred by the ,1 and ,6 subtypes. Structural heterogeneity within these transmembrane and intracellular regions can therefore influence the characteristics of the postsynaptic response of GABAA receptors with different subunit composition. [source]

Distinct pharmacology of rat and human histamine H3 receptors: role of two amino acids in the third transmembrane domain

BRITISH JOURNAL OF PHARMACOLOGY, Issue 7 2000
X Ligneau
Starting from the sequence of the human histamine H3 receptor (hH3R) cDNA, we have cloned the corresponding rat cDNA. Whereas the two deduced proteins show 93.5% overall homology and differ only by five amino acid residues at the level of the transmembrane domains (TMs), some ligands displayed distinct affinities. Thioperamide and ciproxifan were about 10 fold more potent at the rat than at the human receptor, whereas FUB 349 displayed a reverse preference. Histamine, (R),-methylhistamine, proxyfan or clobenpropit were nearly equipotent at H3 receptors of both species. The inverse discrimination patterns of ciproxifan and FUB 349 were partially changed by mutation of one amino acid (V122A), and fully abolished by mutation of two amino acids (A119T and V122A), in TM3 of the rH3R located in the vicinity of Asp114 purported to salt-link the ammonium group of histamine. Therefore, these two residues appear to be responsible for the distinct pharmacology of the H3R in the two species. British Journal of Pharmacology (2000) 131, 1247,1250; doi:10.1038/sj.bjp.0703712 [source]