Coassembly of K(V)LQT1 and minK (IsK) proteins to form cardiac I(Ks) potassium channel

The slowly activating delayed-rectifier K+ current, I(Ks), modulates the repolarization of cardiac action potentials. The molecular structure of the I(Ks) channel is not known, but physiological data indicate that one component of the I(Ks), channel is minK, a 130-amino-acid protein with a single putative transmembrane domain. The size and structure of this protein is such that it is unlikely that minK alone forms functional channels. We have previously used positional cloning techniques to define a new putative K+-channel gene, KVLQT1. Mutations in this gene cause long-QT syndrome, an inherited disorder that increases the risk of sudden death from cardiac arrhythmias. Here we show that KVLQT1 encodes a K+ channel with biophysical properties unlike other known cardiac currents. We considered that K(V)LQT1 might coassemble with another subunit to form functional channels in cardiac myocytes. Coexpression of K(V)LQT1 with minK induced a current that was almost identical to cardiac I(Ks). Therefore, K(V)LQT1 is the subunit that coassembles with minK to form I(Ks) channels and I(Ks) dysfunction is a cause of cardiac arrhythmia.

Positional cloning of a novel potassium channel gene: KVLQT1 mutations cause cardiac arrhythmias

Genetic factors contribute to the risk of sudden death from cardiac arrhythmias. Here, positional cloning methods establish KVLQT1 as the chromosome 11-linked LQT1 gene responsible for the most common inherited cardiac arrhythmia. KVLQT1 is strongly expressed in the heart and encodes a protein with structural features of a voltage-gated potassium channel. KVLQT1 mutations are present in affected members of 16 arrhythmia families, including one intragenic deletion and ten different missense mutations. These data define KVLQT1 as a novel cardiac potassium channel gene and show that mutations in this gene cause susceptibility to ventricular tachyarrhythmias and sudden death.

SCN5A mutations associated with an inherited cardiac arrhythmia, long QT syndrome

Long QT syndrome (LQT) is an inherited disorder that causes sudden death from cardiac arrhythmias, specifically torsade de pointes and ventricular fibrillation. We previously mapped three LQT loci: LQT1 on chromosome 11p15.5, LQT2 on 7q35-36, and LQT3 on 3p21-24. Here we report genetic linkage between LQT3 and polymorphisms within SCN5A, the cardiac sodium channel gene. Single strand conformation polymorphism and DNA sequence analyses reveal identical intragenic deletions of SCN5A in affected members of two unrelated LQT families. The deleted sequences reside in a region that is important for channel inactivation. These data suggest that mutations in SCN5A cause chromosome 3-linked LQT and indicate a likely cellular mechanism for this disorder.

Hemizygosity at the elastin locus in a developmental disorder, Williams syndrome

Williams syndrome (WS) is a developmental disorder affecting connective tissue and the central nervous system. A common feature of WS, supravalvular aortic stenosis, is also a distinct autosomal dominant disorder caused by mutations in the elastin gene. In this study, we identified hemizygosity at the elastin locus using genetic analyses in four familial and five sporadic cases of WS. Fluorescent in situ hybridization and quantitative Southern analyses confirmed these findings, demonstrating inherited and de novo deletions of the elastin gene. These data indicate that deletions involving one elastin allele cause WS and implicate elastin hemizygosity in the pathogenesis of the disease.

Linkage of a cardiac arrhythmia, the long QT syndrome, and the Harvey ras-1 gene

Genetic factors contribute to heart disease. In this study, linkage analyses have been performed in a family that is predisposed to sudden death from cardiac arrhythmias, the long QT syndrome (LQT). A DNA marker at the Harvey ras-1 locus (H-ras-1) was linked to LQT with a logarithm of the likelihood ratio for linkage (lod score) of 16.44 at theta = 0, which confirms the genetic basis of this trait and localizes this gene to the short arm of chromosome 11. As no recombination was observed between LQT and H-ras-1, and there is a physiological rationale for its involvement in this disease, ras becomes a candidate for the disease locus.

Magnetic Domain-Wall Logic

"Spintronics," in which both the spin and charge of electrons are used for logic and memory operations, promises an alternate route to traditional semiconductor electronics. A complete logic architecture can be constructed, which uses planar magnetic wires that are less than a micrometer in width. Logical NOT, logical AND, signal fan-out, and signal cross-over elements each have a simple geometric design, and they can be integrated together into one circuit. An additional element for data input allows information to be written to domain-wall logic circuits.

Why are organisms usually bigger in colder environments? Making sense of a life history puzzle

Environmental effects on body size are of widespread ecological and economic importance but our understanding of these effects has been obscured by an apparent paradox. Life history analysis suggests that it is adaptive for adults to emerge smaller if reared in conditions that slow down juvenile growth. However, whereas smaller adults emerge if growth is limited by food availability, the reverse is usually observed if growth is limited by temperature. The resolution of this apparent paradox may be that the response of adult size to temperature is adaptive, but is constrained by a trade-off that can be understood in terms of von Bertalanffy's classic theory of growth. Alternatively, the response may be the unavoidable consequence of a fundamental relationship between cell size and temperature.

LIM-kinase1 hemizygosity implicated in impaired visuospatial constructive cognition

To identify genes important for human cognitive development, we studied Williams syndrome (WS), a developmental disorder that includes poor visuospatial constructive cognition. Here we describe two families with a partial WS phenotype; affected members have the specific WS cognitive profile and vascular disease, but lack other WS features. Submicroscopic chromosome 7q11.23 deletions cosegregate with this phenotype in both families. DNA sequence analyses of the region affected by the smallest deletion (83.6 kb) revealed two genes, elastin (ELN) and LIM-kinase1 (LIMK1). The latter encodes a novel protein kinase with LIM domains and is strongly expressed in the brain. Because ELN mutations cause vascular disease but not cognitive abnormalities, these data implicate LIMK1 hemizygosity in imparied visuospatial constructive cognition.

The elastin gene is disrupted by a translocation associated with supravalvular aortic stenosis

To identify genes involved in vascular disease, we investigated patients with supravalvular aortic stenosis (SVAS), an inherited vascular disorder that causes hemodynamically significant narrowing of large elastic arteries. Pulsed-field gel and Southern analyses showed that a translocation near the elastin gene cosegregated with SVAS in one family. DNA sequence analyses demonstrated that the translocation disrupted the elastin gene and localized the breakpoint to exon 28. Taken together with our previous study linking SVAS to the elastin gene in two additional families and existing knowledge of vascular biology, these data suggest that mutations in the elastin gene can cause SVAS.

Platelet-activating factor acetylhydrolase deficiency. A missense mutation near the active site of an anti-inflammatory phospholipase

Deficiency of plasma platelet-activating factor (PAF) acetylhydrolase is an autosomal recessive syndrome that has been associated with severe asthma in Japanese children. Acquired deficiency has been described in several human diseases usually associated with severe inflammation. PAF acetylhydrolase catalyzes the degradation of PAF and related phospholipids, which have proinflammatory, allergic, and prothrombotic properties. Thus, a deficiency in the degradation of these lipids should increase the susceptibility to inflammatory and allergic disorders. Miwa et al. reported that PAF acetylhydrolase activity is absent in 4% of the Japanese population, which suggests that it could be a common factor in such disorders, but the molecular basis of the defect is unknown. We show that inherited deficiency of PAF acetylhydrolase is the result of a point mutation in exon 9 and that this mutation completely abolishes enzymatic activity. This mutation is the cause of the lack of enzymatic activity as expression in E. coli of a construct harboring the mutation results in an inactive protein. This mutation as a heterozygous trait is present in 27% in the Japanese population. This finding will allow rapid identification of subjects predisposed to severe asthma and other PAF-mediated disorders.

Two long QT syndrome loci map to chromosomes 3 and 7 with evidence for further heterogeneity

Cardiac arrhythmias cause sudden death in 300,000 United States citizens every year. In this study, we describe two new loci for an inherited cardiac arrhythmia, long QT syndrome (LQT). In 1991 we reported linkage of LQT to chromosome 11p15.5. In this study we demonstrate further linkage to D7S483 in nine families with a combined lod score of 19.41 and to D3S1100 in three families with a combined score of 6.72. These findings localize major LQT genes to chromosomes 7q35-36 and 3p21-24, respectively. Linkage to any known locus was excluded in three families indicating that additional heterogeneity exists. Proteins encoded by different LQT genes may interact to modulate cardiac repolarization and arrhythmia risk.

The structure, physical and chemical properties of the soy bean protein glycinin

The major storage protein of the soybean, glycinin, has been prepared in a homogeneous form and examined by a variety of techniques. It has been found that the protein has a molecular weight of 320000 and contains two sizes of subunits with different isoelectric points. There are six acidic subunits of approximately 35000 and six basic of approximately 20000. Analysis revealed three different kinds of acidic subunits and probably three kinds of basic ones also. These twelve subunits are packed in two identical hexagons, placed one on the other, yielding a hollow oblate cylinder of 110 X 110 X 75 A. Some or all of the subunits are non-spherical resulting in a partial blocking of the central hole. Information about the forces stabilzing the native structure is also discussed.

The complete sequence and structural analysis of human apolipoprotein B-100: relationship between apoB-100 and apoB-48 forms

We have isolated and sequenced overlapping cDNA clones covering the entire sequence of human apolipoprotein B-100 (apoB-100). DNA sequence analysis and determination of the mRNA transcription initiation site by S1 nuclease mapping showed that the apoB mRNA consists of 14,112 nucleotides including the 5' and 3' untranslated regions which are 128 and 301 nucleotides respectively. The DNA-derived protein sequence shows that apoB-100 is 513,000 daltons and contains 4560 amino acids including a 24-amino-acid-long signal peptide. The mol. wt of apoB-100 implies that there is one apoB molecule per LDL particle. Computer analysis of the predicted secondary structure of the protein showed that some of the potential alpha helical and beta sheet structures are amphipathic, whereas others have non-amphipathic neutral to apolar character. These latter regions may contribute to the formation of the lipid-binding domains of apoB-100. The protein contains 25 cysteines and 20 potential N-glycosylation sites. The majority of cysteines are distributed in the amino terminal portion of the protein. Four of the potential glycosylation sites are in predicted beta turn structures and may represent true glycosylation positions. ApoB lacks the tandem repeats which are characteristic of other apolipoproteins. The mean hydrophobicity the mean value of H1 and helical hydrophobic moment the mean value of microH profiles of apoB showed the presence of several potential helical regions with strong polar character and high hydrophobic moment. The region with the highest hydrophobic moment, between amino acid residues 3352 and 3369, contains five closely spaced, positively charged residues, and has sequence homology to the LDL receptor binding site of apoE. This region is flanked by three neighbouring regions with positively charged amino acids and high hydrophobic moment that are located between residues 3174 and 3681. One or more of these closely spaced apoB sequences may be involved in the formation of the LDL receptor-binding domain of apoB-100. Blotting analysis of intestinal RNA and hybridization of the blots with carboxy apoB cDNA probes produced a single 15-kb hybridization band whereas hybridization with amino terminal probes produced two hybridization bands of 15 and 8 kb. Our data indicate that both forms of apoB mRNA contain common sequences which extend from the amino terminal of apoB-100 to the vicinity of nucleotide residue 6300. These two messages may have resulted from differential splicing of the same primary apoB mRNA transcript.

Phase behavior and bilayer properties of fatty acids: hydrated 1:1 acid-soaps

The physical properties in water of a series of 1:1 acid-soap compounds formed from fatty acids and potassium soaps with saturated (10-18 carbons) and omega-9 monounsaturated (18 carbons) hydrocarbon chains have been studied by using differential scanning calorimetry (DSC), X-ray diffraction, and direct and polarized light microscopy. DSC showed three phase transitions corresponding to the melting of crystalline water, the melting of crystalline lipid hydrocarbon chains, and the decomposition of the 1:1 acid-soap compound into its parent fatty acid and soap. Low- and wide-angle X-ray diffraction patterns revealed spacings that corresponded (with increasing hydration) to acid-soap crystals, hexagonal type II liquid crystals, and lamellar liquid crystals. The lamellar phase swelled from bilayer repeat distances of 68 (at 45% H2O) to 303 A (at 90% H2O). Direct and polarized light micrographs demonstrated the formation of myelin figures as well as birefringent optical textures corresponding to hexagonal and lamellar mesophases. Assuming that 1:1 potassium hydrogen dioleate and water were two components, we constructed a temperature-composition phase diagram. Interpretation of the data using the Gibbs phase rule showed that, at greater than 30% water, hydrocarbon chain melting was accompanied by decomposition of the 1:1 acid-soap compound and the system changed from a two-component to a three-component system. Comparison of hydrated 1:1 fatty acid/soap systems with hydrated soap systems suggests that the reduced degree of charge repulsion between polar groups causes half-ionized fatty acids in excess water to form bilayers rather than micelles.(ABSTRACT TRUNCATED AT 250 WORDS)

Matrix description of general motion correction applied to multishot images

Motion of an object degrades MR images, as the acquisition is time-dependent, and thus k-space is inconsistently sampled. This causes ghosts. Current motion correction methods make restrictive assumptions on the type of motions, for example, that it is a translation or rotation, and use special properties of k-space for these transformations. Such methods, however, cannot be generalized easily to nonrigid types of motions, and even rotations in multiple shots can be a problem. Here, a method is presented that can handle general nonrigid motion models. A general matrix equation gives the corrupted image from the ideal object. Thus, inversion of this system allows us to get the ideal image from the corrupted one. This inversion is possible by efficient methods mixing Fourier transforms with the conjugate gradient method. A faster but empirical inversion is discussed as well as methods to determine the motion. Simulated three-dimensional affine data and two-dimensional pulsation data and in vivo nonrigid data are used for demonstration. All examples are multishot images where the object moves between shots. The results indicate that it is now possible to correct for nonrigid types of motion that are representative of many types of patient motion, although computation times remain an issue.

Elastin point mutations cause an obstructive vascular disease, supravalvular aortic stenosis

Supravalvular aortic stenosis (SVAS) is an inherited obstructive vascular disease that affects the aorta, carotid, coronary and pulmonary arteries. Previous molecular genetic data have led to the hypothesis that SVAS results from mutations in the elastin gene, ELN. In these studies, the disease phenotype was linked to gross DNA rearrangements (35 and 85 kb deletions and a translocation) in three SVAS families. However, gross rearrangements of ELN have not been identified in most cases of autosomal dominant SVAS. To define the spectrum of ELN mutations responsible for this disorder, we refined the genomic structure of human ELN and used this information in mutational analyses. ELN point mutations co-segregate with the disease in four familial cases and are associated with SVAS in three sporadic cases. Two of the mutations are nonsense, one is a single base pair deletion and four are splice site mutations. In one sporadic case, the mutation arose de novo. These data demonstrate that point mutations of ELN cause autosomal dominant SVAS.

Automatic correction of motion artifacts in magnetic resonance images using an entropy focus criterion

We present the use of an entropy focus criterion to enable automatic focusing of motion corrupted magnetic resonance images. We demonstrate the principle using illustrative examples from cooperative volunteers. Our technique can determine unknown patient motion or use knowledge of motion from other measures as a starting estimate. The motion estimate is used to compensate the acquired data and is iteratively refined using the image entropy. Entropy focuses the whole image principally by favoring the removal of motion induced ghosts and blurring from otherwise dark regions of the image. Using only the image data, and no special hardware or pulse sequences, we demonstrate correction for arbitrary rigid-body translational motion in the imaging plane and for a single rotation. Extension to three-dimensional (3-D) and more general motion should be possible. The algorithm is able to determine volunteer motion well. The mean absolute deviation between algorithm and navigator-echo-determined motion is comparable to the displacement step size used in the algorithm. Local deviations from the recorded motion or navigator-determined motion are explained and we indicate how enhanced focus criteria may be derived. In all cases we were able to compensate images for patient motion, reducing blurring and ghosting.

Normal newt limb regeneration requires matrix metalloproteinase function

Newts regenerate lost limbs through a complex process involving dedifferentiation, migration, proliferation, and redifferentiation of cells proximal to the amputation plane. To identify the genes controlling these cellular events, we performed a differential display analysis between regenerating and nonregenerating limbs from the newt Notophthalmus viridescens. This analysis, coupled with a direct cloning approach, identified a previously unknown Notophthalmus collagenase gene (nCol) and three known matrix metalloproteinase (MMP) genes, MMP3/10a, MMP3/10b, and MMP9, all of which are upregulated within hours of limb amputation. MMP3/10b exhibits the highest and most ubiquitous expression and appears to account for the majority of the proteolytic activity in the limb as measured by gel zymography. By testing purified recombinant MMP proteins against potential substrates, we show that nCol is a true collagenase, MMP9 is a gelatinase, MMP3/10a is a stromelysin, and MMP3/10b has an unusually broad substrate profile, acting both as a stromelysin and noncanonical collagenase. Exposure of regenerating limbs to the synthetic MMP inhibitor GM6001 produces either dwarfed, malformed limb regenerates or limb stumps with distal scars. These data suggest that MMPs are required for normal newt limb regeneration and that MMPs function, in part, to prevent scar formation during the regenerative process.

Conformational analysis of apolipoprotein A-I and E-3 based on primary sequence and circular dichroism

The primary and secondary structure of human plasma apolipoprotein A-I and apolipoprotein E-3 have been analyzed to further our understanding of the secondary and tertiary conformation of these proteins and the structure and function of plasma lipoprotein particles. The methods used to analyze the primary sequence of these proteins used computer programs: (a) to identify repeated patterns within these proteins on the basis of conservative substitutions and similarities within the physicochemical properties of each residue; (b) for local averaging, hydrophobic moment, and Fourier analysis of the physicochemical properties; and (c) for secondary structure prediction of each protein carried out using homology, statistical, and information theory based methods. Circular dichroism was used to study purified lipid-protein complexes of each protein and quantitate the secondary structure in a lipid environment. The data from these analyses were integrated into a single secondary structure prediction to derive a model of each protein. The sequence homology within apolipoproteins A-I, E-3, and A-IV is used to derive a consensus sequence for two 11 amino acid repeating sequences in this family of proteins.

Thermal unfolding of human high-density apolipoprotein A-1: implications for a lipid-free molten globular state

Apolipoprotein A-1 (apoA-1) in complex with high-density lipoprotein is critically involved in the transport and metabolism of cholesterol and in the pathogenesis of atherosclerosis. We reexamined the thermal unfolding of lipid-free apoA-1 in low-salt solution at pH approximately 7, by using differential scanning calorimetry and circular dichroism. At protein concentrations <5 mg/ml, thermal unfolding of apoA-1 is resolved as an extended peak (25 degrees C-90 degrees C) that can be largely accounted for by a single reversible non-two-state transition with midpoint Tm 57 +/- 1 degree C, calorimetric enthalpy deltaH(Tm)= 200 +/- 20 kcal/mol (1 kcal = 4.18 kJ), van't Hoff enthalpy deltaHv(Tm) approximately 32.5 kcal/mol, and cooperativity deltaHv(Tm)/deltaH(Tm) approximately 0.16. The enthalpy deltaH(Tm) can be accounted for by melting of the alpha-helical structure that is inferred by CD to constitute approximately 60% of apoA-1 amino acids. Farand near-UV CD spectra reveal noncoincident melting of the secondary and tertiary structural elements and indicate a well-defined secondary structure but a largely melted tertiary structure for apoA-1 at approximately 37 degrees C and pH 7. This suggests a molten globular-like state for lipid-free apoA-1 under near-physiological conditions. Our results suggest that in vivo lipid binding by apoA-1 may be mediated via the molten globular apolipoprotein state in plasma.

A rigorous framework for diffusion tensor calculus

In biological tissue, all eigenvalues of the diffusion tensor are assumed to be positive. Calculations in diffusion tensor MRI generally do not take into account this positive definiteness property of the tensor. Here, the space of positive definite tensors is used to construct a framework for diffusion tensor analysis. The method defines a distance function between a pair of tensors and the associated shortest path (geodesic) joining them. From this distance a method for computing tensor means, a new measure of anisotropy, and a method for tensor interpolation are derived. The method is illustrated using simulated and in vivo data.

Hepatic cryosurgery in treating colorectal metastases

BACKGROUND

The purpose of this study was to determine the effectiveness of cryosurgery as an adjunct to resection in treating patients with hepatic metastases from colorectal adenocarcinoma.

METHODS

Forty-seven patients with documented metastases limited to the liver from colorectal adenocarcinoma were treated with cryosurgery with or without resection from November 1987 to February 1992 and were followed until February 1994. Intraoperative ultrasound was used to map the lesions and place the cryoprobes. Each lesion was frozen to -196 degrees centigrade for 15 minutes, thawed for 10 minutes, and frozen again for 15 minutes. Follow-up computed tomographic scans were obtained before hospital discharge and 6 months and 1 year after cryosurgery. Carcinoembryonic antigen levels were obtained monthly.

RESULTS

Thirty-one males and 16 females, with a median age of 63 years, were treated. The median hospital stay was 10 days, and follow-up ranged from 24 to 57 months, with a median follow-up of 26 months. The actual survival at 24 months was 62%. Eleven percent of these patients had no evidence of disease at a median follow-up of 30 months. Complications included myoglobinuria, coagulopathy, pleural effusions, and bile duct injuries. Two patients (4%) died because of multisystem organ failure with irreversible coagulopathies.

CONCLUSIONS

Cryosurgical ablation increases the number of patients with liver metastases who potentially can become disease free. However, the effect on overall survival will require a longer follow-up period.

X-ray diffraction and calorimetric study of anhydrous and hydrated N-palmitoylgalactosylsphingosine (cerebroside)

Differential scanning calorimetry and X-ray diffraction of anhydrous and hydrated N-palmitoylgalactosylsphingosine (NPGS) show evidence of complex polymorphic behavior and interconversions between stable and metastable structural forms. Anhydrous NPGS exhibits three lamellar crystal forms (A, B, and B') at temperatures below 143 degrees C and a liquid-crystal form between 143 and 180 degrees C before melting to an isotropic liquid at 180 degrees C. The crystal B leads to liquid-crystal transition is accompanied by an enthalpy change, delta H, of 11.2 kcal/mol of NPGS, while a relatively small enthalpy change (delta H = 0.8 kcal/mol) marks the liquid-crystal leads to liquid transition. The A and B' crystal forms do not hydrate readily at room temperature. When heated, crystal form A in the presence of water undergoes an exothermic transition at 52 degrees C to produce a thermodynamically stable hydrated crystal E form. X-ray diffraction shows that this stable bilayer crystal form has a highly ordered hydrocarbon chain packing arrangement; melting to the bilayer liquid-crystal form occurs at 82 degrees C with a large enthalpy change, delta H = 17.5 kcal/mol of NPGS. A complex liquid-crystal leads to crystal transition is observed on cooling; the cooling rate independent exotherm involves the transition of the hydrated liquid crystal to an intermediate metastable crystal form identical with anhydrous crystal form A. The subsequent cooling rate dependent step involves the conversion of the metastable crystal form A to the stable crystal form E. We suggest that hydrated crystal form E is stabilized by both a highly ordered chain packing mode and a lateral intermolecular hydrogen bonding network involving the sphingosine backbone, the galactosyl group, and interbilayer water molecules. Although disruption of both the specific hydrogen chain packing and H-bonding networks occurs at the high enthalpy transition to the bilayer liquid-crystal L alpha form, these two types of interactions are not reestablished simultaneously on cooling. First, recrystallization of the hydrocarbon chain accompanies removal of water from the lipid interface, leading to "dehydrated" metastable crystal form A. This is followed by a time-dependent, temperature-dependent hydration process which allows a rearrangement of the hydrogen-bonding matrix. Alterations in the NPGS-NPGS and NPGS-water interactions accompany further changes in the hydrocarbon chain packing and lead to the formation of the stable E form.