Review. SUR1: a unique ATP-binding cassette protein that functions as an ion channel regulator

SUR1 is an ATP-binding cassette (ABC) transporter with a novel function. In contrast to other ABC proteins, it serves as the regulatory subunit of an ion channel. The ATP-sensitive (KATP) channel is an octameric complex of four pore-forming Kir6.2 subunits and four regulatory SUR1 subunits, and it links cell metabolism to electrical activity in many cell types. ATPase activity at the nucleotide-binding domains of SUR results in an increase in KATP channel open probability. Conversely, ATP binding to Kir6.2 closes the channel. Metabolic regulation is achieved by the balance between these two opposing effects. Precisely how SUR1 talks to Kir6.2 remains unclear, but recent studies have identified some residues and domains that are involved in both physical and functional interactions between the two proteins. The importance of these interactions is exemplified by the fact that impaired regulation of Kir6.2 by SUR1 results in human disease, with loss-of-function SUR1 mutations causing congenital hyperinsulinism and gain-of-function SUR1 mutations leading to neonatal diabetes. This paper reviews recent data on the regulation of Kir6.2 by SUR1 and considers the molecular mechanisms by which SUR1 mutations produce disease.     

Effects of long-term androgen administration on breast tissue of female-to-male transsexuals.

Our aim was to examine the effects of androgen administration on breast tissue histology of female-to-male transsexuals and to study the immunohistochemical expression of three human tissue kallikreins, hK3 (PSA), hK6, and hK10. We studied 23 female-to-male transsexuals who were treated with injectable testosterone for 18-24 months. We also used 10 control female breast tissues. All tissues were fixed in buffered formalin, embedded in paraffin, and examined by hematoxylin-eosin staining and immunohistochemical staining for PSA, hK6, and hK10. Females treated with androgens exhibited similar involutionary changes as those seen in breast of menopausal women, such as marked reduction of glandular tissue, involution of the lobuloalveolar structures, and prominence of fibrous connective tissue, but presence of only small amounts of fat tissue. Fibrocystic lesions were generally not observed. In immunohistochemistry, in control breast tissues, we found moderate to strong cytoplasmic immunoexpression of hK6 and hK10 in the epithelial ductal and lobuloalveolar structures, but myoepithelial cells were negative. Luminal secretions were also positive. In menopausal breast, the immunoexpression of hK6 and hK10 was weaker and focal. No control case showed immunoexpression for PSA. In female-to-male transsexuals, one case showed focal PSA cytoplasmic immunoexpression in the epithelium of moderately involuting lobules. Long-term administration of androgens in female-to-male transsexuals causes marked reduction of glandular tissue and prominence of fibrous connective tissue. These changes are similar to those observed at the end-stage of menopausal mammary involution.     

An adaptive chromosomal polymorphism affecting size-related traits,and longevity selection in a natural population ofDrosophila buzzatii

Size-related phenotypic variation among second-chromosome karyotypes inDrosophila buzzatii was examined in an Argentinian natural population. For all measured traits (thorax and wing length; wing, head and face width), this inversion polymorphism exhibited a significant and (additive) linear contribution to the phenotypic variance in newly emerged wild flies. The results suggest that only overall body size, and not body shape, is affected. as no karyotypic variation was found for any trait when the effects of differences in within-karyotype size were removed with Burnaby's method. Likewise, in an experiment of longevity selection in the wild, variation in chromosomal frequencies was verified in the direction predicted on the basis of: (i) previous studies on longevity selection for body size in the wild and (ii) the pattern of chromosomal effects we observed on size. The direction of such selection is consistent with a pattern of antagonistic selection detected in previous studies on the inversion polymorphism.     

Identification of albumin-binding proteins of thymocyte plasmalemma

In the present work we examined whether the interaction between albumin molecules and thymocytes involves albumin-binding proteins (ABP). Two plasmalemma-rich fractions obtained by differential centrifugation from rat thymus lymphocytes were characterized biochemically and morphologically. These fractions were examined by ligand-blotting and ligand affinity chromatography techniques. Plasmalemma proteins separated by SDS-PAGE were electrotransferred onto nitrocellulose membranes and incubated with¹²⁵I-albumin, in the presence or absence of excess native albumin. The autoradiogram revealed specific binding to two sets of polypeptides of 16–18 and 29–31 kDa, which could be blocked by native albumin. To elucidate whether albumin-binding proteins are exposed on the cell surface, intact lymphocytes were surface radioiodinated and membrane fractions prepared from them were subjected to affinity chromatography on albumin-agarose beads. The proteins thus purified had, like ABP, M_r of 16 and 31. These data indicate that ABP (i) are components of thymocyte plasma membrane, (ii) have apparent molecular mass of 16–18 and 29–31 kDa, and (iii) are exposed on the outer membrane surface.Abbreviations ABP albumin-binding proteins - Alb bovine serum albumin - Au gold - DAPI 4,6-diamidino-2-phenylindol - EM electron microscopy - NC nitrocellulose - PAGE polyacrylamidegel electrophoresis - PBS phosphate buffered saline - PEG polyethylene glycol - PMSF phenylmethylsulfonyl fluoride - WGA Wheat germ agglutinin     

Hydration of cis and trans N-methylformamide as revealed by the use of 17O-NMR,molecular mechanics,and ab initio calculations

The solvation of cis and trans N-methylformamide (NMF) by water was investigated using a combination of ¹⁷O-nmr spectroscopy, classical molecular mechanics [MM2(77) and MM2(87)] force field, and ab initio 4-31G* gradient optimization calculations. In dilute aqueous solution, the ¹⁷O-nmr spectra of NMF indicate strong shielding by 66.9 and 66.1 ppm for the cis and trans amide oxygens, respectively, compared to those values obtained in dilute toluene solution. This demonstrates that both isomers are equally solvated by molecules of water, which are further hydrogen bonded to molecules of water of the bulk solvent. Molecular mechanics simulations were carried out for cis and trans NMF in a cluster of water molecules. Radial distribution functions show structural contacts by several water molecules at the amide CO and NH group, which are significantly more pronounced with MM2 (87) calculations. Ab initio 4-31G* gradient optimization calculations on the supermolecule trans NMF-(H₂O)₃ indicates the presence of more than two hydrogen-bond contacts at the carbonyl oxygen. This is in agreement with MM2 calculations and provides further evidence for multiple acceptor properties of the amide oxygen and an out of the amide plane arrangement of the bound molecules of water. Comparison of the integration data to the first radial distribution function (rdf) minima shows that the local solvation of the CO and NH groups is very similar for both cis and trans isomers. The intermolecular geometric parameters of the supermolecule trans NMA–(H₂O)₃ and the first rdf maxima resulting from MM2 (87) and MM2 (77) calculations are compared with distribution of water molecules around the CO and NH groups of peptides and proteins resulting from x-ray and neutron diffraction experiments. The rdfs involving the methyl group of NMF demonstrate the nonrandom distribution of solvent sites with first maxima in reasonable agreement with distribution of water molecules around the apolar side chain of amino acid residues in proteins. © 1995 John Wiley & Sons, Inc.     

The sulfate ligand as a promising “player” in 3d-metal cluster chemistry

The potentiality of the sulfate ligand in the chemistry of polynuclear 3d-metal complexes (clusters) is illustrated through few, representative examples from our own research. A systematic search from the Cambridge Crystallographic Data Base reveals that the ligand can adopt 16 different bridging coordination modes, being capable of linking 2, 3, 4, 5, 6, 8 or even 10 metal ions. Despite its tremendous structural flexibility, the use of the ligand in synthetic 3d-metal cluster chemistry has been largely neglected. This report shows that the sulfate ions, in combination with anions of di-2-pyridyl ketone or various 2-pyridyl oximes are versatile ligand “blends” for the synthesis of interesting Ni(II) and Zn(II) clusters with interesting structures and properties. A prognosis for the future is attempted.     

Human kallikrein 13 expression in normal tissues: an immunohistochemical study.

The human tissue kallikrein 13 gene (KLK13), encoding for hK13 protein, was recently cloned and characterized. Here we describe the immunohistochemical (IHC) localization of hK13 in normal human tissues and compare it with the expression of two other kallikreins, hK6 and hK10. We performed the streptavidin-biotin IHC method on 204 paraffin blocks from archival, current, and autopsy material prepared from almost every normal human tissue, using a polyclonal and a monoclonal hK13 antibody. The staining was cytoplasmic and both antibodies yielded similar results. The hK13 protein was revealed in a variety of tissues, mainly in glandular epithelia. Other epithelia that expressed hK13 included the urothelium, the spermatic epithelium, and the epithelium of the choroid plexus. hK13 was intensely immunoexpressed by some endocrine organs, such as the adenohypophysis, the thyroid gland, the parathyroid glands, the adrenal medulla, the Leydig cells of the testis, and the cells of the endocrine pancreas. Immunoreactivity was also observed in the primordial follicles, the corpus luteum, and sparse luteinized cells in the stroma of the ovary, the trophoblastic cells of the placenta, the Hassall's corpuscles of the thymus, and chondrocytes. Nerves and ganglia of the peripheral nervous system, and both neurons and glial cells in the central nervous system, were positive. In short, hK13 was expressed by many glandular epithelia, some endocrine organs, and some specialized epithelia and cells. Comparison of these data with hK6 and hK10 expression suggests that the three kallikreins have a similar IHC pattern in normal human tissues.     

INVERSION POLYMORPHISM,LONGEVITY, AND BODY SIZE IN A NATURAL POPULATION OF DROSOPHILA BUZZATII

In this study we present the results of an analysis of differential longevity associated with Drosophila buzzatii second chromosome inversion karyotypes based on the assessment of more than 1000 individuals collected in a natural population. Comparisons of inversion frequencies between emerged and bait-collected flies showed not only that inversion arrangements were associated with differential longevity, but also that selection was sex specific. Because each individual fly was scored for thorax length and karyotype, we were able to show that longevity selection favoring larger flies coupled with the average effect of inversions on thorax length can account for the change of inversion frequencies due to longevity in females. The observed genotypic-by-sex interaction could be an important mechanism involved in the maintenance of the polymorphism. Arrangement 2Jz³, which was shown to impaired fecundity in two independent previous studies, exhibited a positive effect on longevity. This pattern of negative pleiotropy may be another plausible mechanism accounting for the maintenance of the polymorphism.     

Characterization of a Photosystem II core and its three-dimensional crystals

A photosystem II core from spinach containing the chlorophyll-binding proteins 47 kDa, 43 kDa, the reaction center proteins D1, D2 and cytochromeb ₅₅₉ and three low molecular weight polypeptides (MW < 10 kDa) was isolated, its three-dimensional crystals were prepared, and both core and crystals were studied by spectroscopic techniques and electron microscopy. The absorption spectra of the crystallized form of the core indicate a specific orientation of the various pigments within the crystal.