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At least 685 records · Page 38Linked to original sources
PubMed2005

Antibody neutralization escape mediated by point mutations in the intracytoplasmic tail of human immunodeficiency virus type 1 gp41.

The persistence of human immunodeficiency virus type 1 (HIV-1) infection in the presence of robust host immunity has been associated in part with variation in viral envelope proteins leading to antigenic variation and escape from neutralizing antibodies. Previous studies of natural neutralization escape mutants have predominantly focused on gp120 and gp41 ectodomain sequence variations that alter antibody binding via changes in conformation or glycosylation pattern of the Env, likely due to the immune pressure exerted on the exposed ectodomain component of the glycoprotein. Here, we show for the first time a novel mechanism by which point mutations in the intracytoplasmic tail of the transmembrane component (gp41) of envelope can render the virus resistant to neutralization by monoclonal antibodies and broadly neutralizing polyclonal serum antibodies. Point mutations in a highly conserved structural motif within the intracytoplasmic tail resulted in decreased binding of neutralizing antibodies to the Env ectodomain, evidently due to allosteric changes both in the gp41 ectodomain and in gp120. While receptor binding and infectivity of the mutant virus remained unaltered, the changes in Env antigenicity were associated with an increase in neutralization resistance of the mutant virus. These studies demonstrate the structurally integrated nature of gp120 and gp41 and underscore a previously unrecognized potentially critical role for even minor sequence variation of the intracytoplasmic tail in modulating the antigenicity of the ectodomain of HIV-1 envelope glycoprotein complex.

Antibody Specificity↗
PubMed2002

Novel point mutation in the cardiac transcription factor CSX/NKX2.5 associated with congenital heart disease.

The homeobox transcription factor CSX/NKX2.5, which is a vertebrate homologue of the Drosophila gene tinman, is essential for cardiac development. It is expressed in the early cardiac mesoderm and in heart muscle lineage throughout life. Homozygous deletion of CSX/NKX2.5 causes early embryonic lethality in mice because cardiac development is arrested at the linear heart tube stage. Heterozygous mutation of human CSX/NKX2.5 has been associated with various congenital heart diseases such as atrial septal defect (ASD), ventricular septal defect, tetralogy of Fallot, and tricuspid valve abnormalities, including Ebstein's anomaly. Additionally, CSX/NKX2.5 mutation causes atrioventricular (AV) conduction block with or without associated congenital heart diseases. Ten different heterozygous mutations have been already reported and a new point mutation, which is a C-to-A transition (Cys264ter) at nucleotide 901 of CSX/NKX2.5, results in the production of a truncated protein occurring COOH-terminal to the homeodomain of CSX/NKX2.5. The mutation was found in a patient with familial ASD and first-degree AV block; 4 members from 3 generations had secundum-type ASD and first-degree AV block.

Cysteine↗
PubMed2006

Point mutations in the juxtamembrane domain of FLT3 define a new class of activating mutations in AML.

In acute myeloid leukemia (AML), two clusters of activating mutations are known in the FMS-like tyrosine kinase-3 (FLT3) gene: FLT3-internal tandem duplications (FLT3-ITDs) in the juxtamembrane (JM) domain in 20% to 25% of patients, and FLT3 point mutations in the tyrosine-kinase domain (FLT3-TKD) in 7% to 10% of patients, respectively. Here, we have characterized a new class of activating point mutations (PMs) that cluster in a 16-amino acid stretch of the juxtamembrane domain of FLT3 (FLT3-JM-PMs). Expression of 4 FLT3-JM-PMs in interleukin-3 (IL-3)-dependent Ba/F3 cells led to factor-independent growth, hyperresponsiveness to FLT3 ligand, and resistance to apoptotic cell death. FLT3-JM-PM receptors were autophosphorylated and showed a higher constitutive dimerization rate compared with the FLT3-wild-type (WT) receptor. As a molecular mechanism, we could show activation of STAT5 and up-regulation of Bcl-x(L) by all FLT3-JM-PMs. The FLT3 inhibitor PKC412 abrogated the factor-independent growth of FLT3-JM-PM-expressing cells. Compared with FLT3-ITD and FLT3-TKD mutants, the FLT3-JM-PMs showed a weaker transforming potential related to lower autophosphorylation of the receptor and its downstream target STAT5. Mapping of the FLT3-JM-PMs on the crystal structure of FLT3 showed that these mutations reduce the stability of the autoinhibitory JM domain, and provides a structural basis for the transforming capacity of this new class of gain-of-function mutations of FLT3.

Amino Acid Sequence↗
PubMed1993

MELAS point mutation with unusual clinical presentation.

Mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (MELAS) is a multisystemic mitochondrial disorder (Pavlakis et al. Advances in Contemporary Neurology. Philadelphia: Davis, 1988: 95-133) and most patients with the typical MELAS phenotype have a point mutation in mitochondrial DNA, an A to G transition at nucleotide 3243 (Goto et al. Nature 1990; 348; 651-653; Koboyashi et al. Biochem Biophys Res Commun 1990; 173: 816-822; Ciafaloni et al. Ann Neurol 1992; 31: 391-398). A 9-yr-old boy presenting with chronic asthma and depression was found to have abnormal mitochondria, partial defects of respiratory chain enzymes, and the MELAS point mutation.

Acid-Base Imbalance↗
PubMed1996

Introducing a point mutation identified in a patient with pituitary resistance to thyroid hormone (Arg 338 to Trp) into other mutant thyroid hormone receptors weakens their dominant negative activities.

Clinical resistance to thyroid hormone (RTH) has been classified into generalized resistance to thyroid hormone (GRTH) and pituitary resistance to thyroid hormone (PRTH) types. Since similar mutations have been identified in tri-iodothyronine (T3) receptor (TR) beta gene in GRTH and PRTH, and since considerable overlap has been seen in the clinical manifestations in patients with GRTH and PRTH, two subtypes of RTH are now considered to be a continuous spectrum with the same genetic defect. A point mutation at amino acid Arg 338 to Trp (R338W) which we identified in a patient with PRTH is very interesting, since R338W has been found in several other patients with PRTH, raising the possibility that this mutation may tend to associate with a phenotype of PRTH. In our previous study, we found that R338W had relatively less impaired transcriptional potency, weaker dominant negative activity on various T3 response elements and poor homodimer formation, as compared with another GRTH mutant. In this study, to investigate the functional properties of R338W further, especially in terms of the relation between transcriptional activity and dimer formations, we introduced the R338W mutation into the mutant receptors, K443E and F451X, constructing the double mutants, R338W/K443E and R338W/ F451X. Both R338W/K443E and R338W/F451X showed negligible T3 binding and transcriptional activities. The dominant negative activities of K443E and F451X were, however, significantly weakened by introducing the R338W mutation. As a control, a double mutant G345R/K443E was constructed by introducing a point mutation, G345R, located in the same exon 9 as R338W, into the K443E mutant. Dominant negative activity did not differ between G345R/K443E and K443E. Homodimer formation was significantly reduced in the double mutants containing R338W, but not G345R. In summary, introducing the R338W mutation, but not G345R, into the mutant TR significantly weakened the dominant negative activity, despite further impairment of the T3 binding and transcriptional activities.

Cells, Cultured↗
PubMed1994

Photosynthetic deficiency of a pufX deletion mutant of Rhodobacter sphaeroides is suppressed by point mutations in the light-harvesting complex genes pufB or pufA.

The pufX gene of the facultative phototroph Rhodobacter sphaeroides encodes a membrane protein that is required for photoheterotrophic growth. Deletion of pufX impairs the photosynthetic generation of a transmembrane potential, suggesting a role for the PufX protein in light-driven cyclic electron transfer [Farchaus, J. W., et al. (1992) EMBO J. 11, 2779-2788]. Here we describe the isolation and characterization of 65 spontaneous suppressor mutants in which photosynthetic competence was restored by secondary mutations. Genetic analysis revealed the occurrence of single point mutations altering highly conserved residues within the light-harvesting complex, B875. One of three tryptophan codons was changed to stop or arginine codons in 89% of these suppressor mutants. Spectral characterization and Western blot analysis were used to examine the B875 assembly and the stable expression of the altered light-harvesting polypeptides. Three different groups of suppressor mutants were found: (1) No stable expression of altered B875 polypeptides was detected for the alpha 43W-->* and beta 44W-->* mutants. (2) There was expression of the mutated B875-beta chain, but no stable B875 assembly in the beta 47W-->R mutants. (3) Intact B875 complexes were found for the alpha 47S-->F or beta 20H-->R mutants. These results provide evidence that the differently altered B875 polypeptides do not substitute directly for the PufX protein but lead to structural rearrangements in the macromolecular membrane organization, thus restoring a sufficiently high capacity for light-driven cyclic electron transfer.

Amino Acid Sequence↗
PubMed2000

Unique enamel phenotype associated with amelogenin gene (AMELX) codon 41 point mutation.

Different mutations in the amelogenin gene (AMELX) result in the markedly different enamel phenotypes that are collectively known as amelogenesis imperfecta (AI). We hypothesize that unique phenotypes result from specific genetic mutations. The purpose of this study was to characterize the enamel compositional and structural features associated with a specific AMELX mutation in three families with X-linked AI. We performed mutational analysis by amplifying AMELX exons and sequencing the products. Permanent and primary affected (N = 6) and normal (N = 3) teeth were collected and examined by light, scanning, and transmission electron microscopy. Enamel proteins were evaluated by immunolocalization of amelogenin and amino acid analysis. AI-affected individuals all shared a common AMELX point mutation (C to A change at codon 41). The dental phenotypic findings were remarkably consistent in all affected individuals. The AI enamel was opaque, with numerous prism defects or holes encompassing the entire prism width. Affected crystallites appeared more radiolucent and morphologically less uniform, compared with that of normal enamel. Immunogold labeling with anti-amelogenin antibodies localized amelogenin to the crystallites but not to the inter-crystalline spaces. No immunogold labeling was seen in normal enamel. There was an increased and amelogenin-like protein content in AI enamel (0.95%) compared with normal enamel (0.13%). We conclude that this codon 41 C to A missense point mutation, in a highly conserved region of the AMELX gene, results in a remarkably consistent phenotype.

Amelogenesis Imperfecta↗
PubMed1995

Absence of RET proto-oncogene point mutations in sporadic hyperplastic and neoplastic lesions of the parathyroid gland.

We investigated the possible role of RET proto-oncogene mutations in the development of sporadic hyperplastic, benign, and malignant parathyroid lesions. DNA extracted from paraffin-embedded specimens of forty parathyroid lesions was screened for RET proto-oncogene point mutations in exons 10, 11, and 16 by nonisotopic polymerase chain reaction-based single-strand conformation polymorphism and heteroduplex gel electrophoresis. The nucleotide sequence of samples with aberrant band patterns was identified by nonisotopic direct sequencing of polymerase chain reaction-amplified DNA. Parathyroids of seven patients with multiple endocrine neoplasia type 2A (MEN 2A) and MEN 2B served as positive controls. None of the eight hyperplastic lesions, three cases of parathyromatosis, ten parathyroid adenomas, eleven carcinomas or one normal parathyroid gland contained mutations in each of the three RET exons tested. Six MEN-2A-associated hyperplastic glands exhibited identical band shifts in the polymerase chain reaction single-strand conformation polymorphism analysis of exon 11, which corresponded to a Cys 634-->Arg substitution in the nucleotide sequence analysis (TGC-->CGC), whereas in the MEN 2B parathyroid specimen a point mutation was found at codon 918 of exon 16 (ATG-->ACG), causing a Met 918-->Thr substitution. Our data indicate that RET mutations of the MEN 2 loci in exons 10, 11, and 16 are not involved in the development of sporadically occurring benign or malignant parathyroid lesions. Furthermore, our results are in accordance with the observation that MEN 2A patients with Cys 634-->Arg (germline) mutations have a higher risk of developing parathyroid disease than those with other mutations at codon 634.

Adenoma↗
PubMed1999

Automated detection of point mutations by electrophoresis in peptide-nucleic acid-containing gels.

Polymerization of electronically, essentially neutral peptide nucleic acids (PNA) into polyacrylamide gels creates a medium in which the salt-independent properties of PNA/DNA interactions are used to achieve hybridization with target DNA during affinity electrophoresis. Such physical entrapment of PNA has been used to differentiate between a retarded, complementary DNA strand and a non-retarded sequence differing by a single point mutation. Analysis of fluorescent PCR products--from both model mismatches and clinically relevant point mutations using a conventional automated DNA sequencer--allows one to follow this hybridization in real time and to distinguish homo- and heterozygous mutants visually. It has been shown that parameters affecting the resolution of these species include not only temperature and concentration (as a function of the [GC] content of the PNA), but also the position of the PNA binding sequence within the interacting DNA segment. Under conditions optimized in terms of temperature and PNA concentration, the maximum separation of retarded from non-retarded DNA single strands is obtained when the PNA binding sequence is close to either DNA terminus. Strategies of PNA and PCR primer design that permit a diagnostic application ranging over 85-451 DNA base pairs are proposed.

Autoanalysis↗
PubMed2000

MELAS with the mitochondrial DNA 3243 point mutation: a neuropathological study.

We performed a neuropathological examination of the central nervous system from seven autopsied patients with mitochondrial myopathy, encephalopathy, lactic acidosis and stroke-like episodes (MELAS). Five of the seven cases were confirmed to have the mitochondrial DNA (mtDNA) 3243 point mutation. In addition to the changes reported previously, diffuse atrophy of the cerebral and cerebellar cortices, diffuse gliosis of cerebral and cerebellar white matter, and cactus formation of Purkinje cells were observed. Electron microscopy revealed accumulation of mitochondria in the cactus formations. These lesions are common in MELAS with the mtDNA 3243 point mutation, but cannot be explained solely by mitochondrial angiopathy, and suggest that intrinsic mitochondrial malfunction contributes to neuronal damage in MELAS pathology. Moreover, the pathological changes observed in the cerebellum suggest that cerebellar function should be evaluated more carefully at the clinical level.

Adult↗
PubMed1993

Invasive human pituitary tumors express a point-mutated alpha-protein kinase-C.

Protein kinase-C (PKC) is a ubiquitous eukaryotic kinase that plays a key role in transmembrane signaling and influences important cellular processes, such as proliferation. Increases in its activity and expression have been demonstrated in adenomatous human pituitaries, with protein expression being the highest in invasive tumors (1). Moreover, in these same invasive tumors, the mean increase in expression (8.9-fold) does not correlate with the mean increase in activity (2.6-fold), suggesting a dysfunction in PKC in these tumors. Here, we show that the PKC alpha-isoform (alpha PKC) is overexpressed in human pituitary tumors. The complete sequencing of the PKC cDNA from four invasive tumors has revealed a point mutation that is absent in the noninvasive tumors analyzed. The point mutation is located at position 294 of the protein, in the V3 region, leading to a substitution of a negatively charged aspartic acid by an apolar glycine. Thus, not only is alpha PKC overexpressed in human pituitary tumors, but it is also structurally altered in the invasive subpopulation of these tumors.

Amino Acid Sequence↗
PubMed1989

Point mutations in both transforming and non-transforming codons of the N-ras proto-oncogene of Ph+ leukemias.

The distribution and frequency of point mutations in the first and second coding exons of the N-ras proto-oncogene was examined in 6 cases of Philadelphia positive (Ph+) hemopoietic malignancies. To increase the detection sensitivity of the mutations and to estimate more accurately the frequency of abnormal alleles in the hemopoietic cell population, a polymerase chain reaction (PCR)/shotgun cloning/double stranded DNA sequencing method was used. Mutations activating the ras oncogenes involving codon 61 were observed in 5 out of 6 cases; in one of these cases (CML3), mutation at codon 61 involved a two base transition. Mutations involving codon 59 were also observed in one case (CML1). In longitudinal studies of 3 cases of chronic myelogenous leukemia samples obtained at the time of initial diagnosis and 5 to 7 years later, a multiplicity of mutations were detected at the time of initial diagnosis prior to any therapy. In one case (CML3), a mutation in codon 61 detected at diagnosis was still present 5 years later, in a second case (CML1) a mutation in codon 61 appeared during the course of the disease and persisted for at least one year, and in the third case (CML2) a mutation in codon 61 was present at diagnosis but absent 5 years later. In one instance (CML1) a mutation in codon 59 was present at the time of initial diagnosis but was not detectable in later samples. Several other point mutations leading to aminoacid changes were scattered predominately through the second exon but were not consistently detected in longitudinal studies on cells from the same patient. The data suggest that there is considerable genetic instability in the 2nd exon of N-ras in the myeloid leukemias but in every case a small subset of cells contains the mutations and these cells do not have a proliferative advantage.

Adult↗
PubMed1998

Characterization of a point mutation in the hormone binding domain of the estrogen receptor from an breast tumor.

It is clear that growth of the MCF-7 breast cancer cell line is stimulated by estrogen and when estrogen is removed, growth slows. We have observed a tumor derived from MCF-7 cells that grows in athymic mice in the absence of estrogen stimulation. We hypothesized that a mutation in the estrogen receptor (ER) could be responsible for this constitutive growth. Using single stranded conformational polymorphism (SSCP) and DNA sequencing analysis, we have identified an ER containing a point mutation at position 415 (gly to val) within the hormone binding domain. The functional activity of this mutant was assessed in vitro and in vivo. Using transient transfection into an ER negative breast cancer cell with an ERE luciferase reporter gene, we found that both the wild-type and mutant receptors have similar efficacy. Additionally, the estrogenic responses were blocked by antiestrogens in a concentration related manner. We also found that tumors with the mutant receptor show similar growth response in athymic mice as wild-type: stimulation with estradiol and inhibition with antiestrogens. We conclude that the point mutation at position 415 (gly to val) is not responsible for constitutive growth.

Animals↗
PubMed1993

H-ras-1 point mutations in soft tissue sarcomas.

The H-ras-1 protooncogene is activated by single base substitutions occurring in either codon 12, 13, or 61. These mutations have been described with varying frequencies in several human tumor types. Since ras oncogenes were first discovered as the transforming sequences of Harvey and Kirsten murine sarcoma viruses (which also contain activating point mutations compared to the homologous cellular sequences), we wished to investigate the possibility that ras mutations might also occur in human sarcomas. We extracted DNA from six malignant fibrous histiocytomas (MFH), three embryonal rhabdomyosarcomas (ER), one alveolar rhabdomyosarcoma, one pleomorphic rhabdomyosarcoma, and one leiomyosarcoma. The DNA from regions flanking codons 12/13 and codon 61 was amplified by the polymerase chain reaction and sequenced with an automated DNA sequencer. As controls, we amplified and sequenced normal DNA (placenta) and DNA with known point mutations (T24 bladder carcinoma cells). We found three cases with mutations, all occurring in codon 12. One ER showed a G-to-T mutation in the second position of codon 12 (coding for valine instead of glycine). Two MFHs showed G-to-A mutations in the second position of codon 12 (coding for aspartic acid instead of glycine). Although a limited number of cases were sampled, we conclude that study of H-ras-1 mutations may be relevant to MFH and ER. Additional studies of N and K-ras mutations as well as more cases investigating H-ras will be required before we can ascertain the significance of ras mutations in the oncogenesis of human soft tissue sarcomas.

Base Sequence↗
PubMed2000

CoMFA-based prediction of agonist affinities at recombinant wild type versus serine to alanine point mutated D2 dopamine receptors.

Agonist affinity changes dramatically as a result of serine to alanine mutations (S193A, S194A, and S197A) within the fifth transmembrane region of D2 dopamine receptors and other receptors for monoamine neurotransmitters. However, agonist 2D-structure does not predict which drugs will be sensitive to which point mutations. Modeling drug-receptor interactions at the 3D level offers considerably more promise in this regard. In particular, a comparison of the same test set of agonists across receptors differing minimally (point mutations) offers promise to enhance the understanding of the structural bases for drug-receptor interactions. We have previously shown that comparative molecular field analysis (CoMFA) can be applied to comparisons of affinity at recombinant D1 and D2 dopamine receptors for the same set of agonists, a differential QSAR. Here, we predicted agonist K(L) for the same set of agonists at wild type D2 vs S193A, S194A, and S197A receptors using CoMFA. Each model used bromocriptine as the template. ln(1/K(L)) values for the low-affinity agonist binding conformation at recombinant wild type and mutant D2 dopamine receptors stably expressed in C6 glioma cells were used as the target property for the CoMFA of the 16 aligned agonist structures. The resulting CoMFA models yielded cross-validated R(2) (q(2)) values ranging from 0.835 to 0.864 and simple R(2) values ranging from 0.999 to 1.000. Predictions of test compound affinities at WT and each mutant receptor were close to measured affinity values. This finding confirmed the predictive ability of the models and their differences from one another. The results strongly support the idea that CoMFA models of the same training set of compounds applied to WT vs mutant receptors can accurately predict differences in drug affinity at each. Furthermore, in a "proof of principle", two different templates were used to derive the CoMFA model for the WT and S193A mutant receptors. Pergolide was chosen as an alternate template because it showed a significant increase in affinity as a result of the S193A mutation. In this instance both the bromocriptine- and pergolide-based CoMFA models were similar to one another but different from those for the WT receptor using bromocriptine- or pergolide- as templates. The pergolide-based S193A model was more strikingly different from that of the WT receptor than was the bromocriptine-based S193A model. This suggests that a "dual-template" approach to differential CoMFA may have special value in elucidating key differences across related receptor types and in determining important elements of the drug-receptor interaction.

Alanine↗
PubMedDate not supplied

Detection of point mutation for human growth hormone in patients with anti-pituitary antibody positive type 1 diabetes mellitus.

We investigated genetic mutations in the coding region of the human growth hormone (hGH) gene in anti-pituitary antibody (APA)-positive patients with type 1 diabetes mellitus (n = 6) or autoimmune thyroid diseases (n = 10) and in APA-negative, healthy controls (n = 10). A point mutation in the hGH gene was discovered in two patients with type 1 diabetes mellitus. No mutations were found in the hGH gene in control subjects, patients with autoimmune thyroid diseases (Hashimoto's thyroiditits, Graves' disease) or in the remaining four patients with type 1 diabetes mellitus. The mutation was located in the coding region for the second amino acid in the N-terminal region of hGH. This point mutation was identified in codon 2 in exon 2 of the hGH gene. We successfully developed an allele-specific amplification method for detecting this mutation using the polymerase chain reaction.

Adolescent↗
PubMed1993

A model to describe how a point mutation of the estrogen receptor alters the structure-function relationship of antiestrogens.

The antiestrogen tamoxifen [(Z)-1(p-beta-dimethylamino-ethoxyphenyl)-1,2- diphenylbut-1-ene] is an effective anticancer agent for the treatment of hormone responsive breast cancer. Previous studies have demonstrated that a point mutation in the estrogen receptor (ER) resulted in an alteration of the pharmacology of 4-hydroxytamoxifen, the active metabolite of tamoxifen (Jiang et al, Mol Endocrinol 6:2167-2174, 1992). We have extended our studies to evaluate the effect of a point mutation, a Val substitution for Gly at amino acid 400 in the ligand binding domain of ER, on the pharmacology of other antiestrogens in ER stable transfectants derived from the ER-negative breast cancer cell line MDA-MB-231 CL10A. The compounds were tested with or without estradiol-17 beta (E2) for their effects on cell growth in cells expressing the wild type ER (S30) or the mutant ER (ML alpha 2H) or in control antisense ER transfectant AS23 which does not express ER protein. MCF-7 cells, which express the wild type ER, were also used as a control. The growth of AS23 cells was not affected by any of the compounds at a concentration of 1 microM. E2 stimulated the growth of MCF-7 cells but inhibited the growth of ER transfectants S30 and ML alpha 2H. The ML alpha 2H cells were about 10 to 100-fold less sensitive to E2 and antiestrogens than S30 and MCF-7 cells. Keoxifene, an antiestrogen with a high affinity for the ER, maintained antiestrogenic activities in both ER transfectants and MCF-7 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗
PubMed2001

The relative contributions of recombination and point mutation to the diversification of bacterial clones.

Low levels of recombination in bacterial species have often been inferred from the presence of linkage disequilibrium between the alleles at different loci in the population. However, significant linkage disequilibrium is inevitable in organisms that divide by binary fission, and recombinational replacements must be very frequent, compared to point mutation, to dissipate disequilibrium. Recent studies using data from multilocus sequence typing indicate that, in many species, recombinational replacements contribute more greatly to clonal diversification than do point mutations and, in some species, recombination has been sufficient to eliminate any phylogenetic signal from gene trees. Recent efforts to improve understanding of the extent and impact of homologous recombination in the diversification of bacterial clones are discussed.

Bacteria↗