False negative cytologic diagnosis of breast carcinoma.

OBJECTIVE: To study the reasons for interpretive errors in false negative diagnosis of breast carcinoma on fine needle aspiration cytology material. STUDY DESIGN: We reviewed only those histologically proved malignant cases where the cytologic material was abnormal and to some extent misinterpreted. RESULTS: There were four lobular carcinomas and one each case of in situ, infiltrating duct, medullary and tubular carcinoma. Smears of lobular carcinomas were hypocellular overall, and the cells showed minimal nuclear pleomorphism. In situ, medullary and tubular carcinoma were associated with fibrocystic changes. The presence of bipolar cells and stromal fragments was misleading in cases of infiltrating duct carcinoma. CONCLUSION: The presence of associated fibrocystic disease may be a misleading factor since it may mask a malignancy. Hypocellularity and relatively nuclear monomorphism were the most common reasons for failure to diagnose malignant breast lesions. Careful attention should be paid to extreme nuclear monomorphism and absence of naked bipolar cells. A cytologically atypical or suspicious diagnosis together with radiologic suspicion should suggest a diagnosis of malignancy.     

Calcium binding mode of gamma-carboxyglutamic acids in conantokins.

Conantokin-T (con-T) and conantokin-G (con-G) are two highly homologous peptide toxins found in Conus venom. The former is a 21-residue peptide with four gamma-carboxyglutamic acid (Gla) residues (at positions 3, 4, 10 and 14), while the latter is a 17-residue peptide with five gamma-carboxyglutamic acid residues (at positions 3, 4, 7, 10 and 14). Despite the apparent similarity in number and relative positions of the gamma-carboxyglutamic acid residues, (113)Cd-NMR studies indicated a distinct metal binding behavior for con-G and con-T. There appears to be four binding sites in con-G in contrast to one metal binding site in con-T. To elucidate the mode of calcium binding by the gamma-carboxyglutamic acid residues in these conantokins, we designed various analogous peptides with their gamma-carboxyglutamic acid replaced by other amino acid residues. (113)Cd-NMR experiments on conantokin analogues reveal that the major difference in the number of metal binding sites between con-G and con-T is due to the residue at position 7. We also performed molecular simulations to calculate the relative binding free energies of several potential binding sites. Based on our theoretical and experimental results, we propose a 'four-site' binding model for conantokin-G and a 'single-site' binding model for conantokin-T.     

GENETIC AND MORPHOLOGICAL VARIATION OF POPULATIONS BELONGING TO THE BULINUS TRUNCATUS/TROPICUS COMPLEX (GASTROPODA; PLANORBIDAE) IN SOUTH WESTERN ZIMBABWE

Aquatic snails from south western Zimbabwe belonging to theBulinus trunscatus/tropicus complex vary widely in shell formsuggesting that more than one taxon could be present. This possibilitywas investigated by making observations on snail samples from13 populations from the Plumtree area, in respect of allozymevariation (5 polymorphic loci), shell morphology (9 variables),copulatory organ and chromosome number. Comparative data wereobtained from snails from north western Zimbabwe identifieddefinitely as B. tropicus. Analysis of the genetic structurerevealed a high degree of polymorphism (P) ranging from 0.29–0.80among populations from Plumtree and expected heterozygosity(H_e) from 0.02–0.22. No enzymatic diagnostic loci werefound which could differentiate the different morphs or populationsand discriminant function analysis on the morphological datashowed an overlap of morphs among populations. Snails analyzedfor chromosome number were all diploid (2n = 36). Snails exposedto Schistosoma haematobium mira-cidia were all refractory. Thisinformation supports the view of a single species, B. tropicus,which is differentiated due to migration barriers and whereenvironmental variables might be implicated in the morphometricdivergence. (Received 31 July 1995; accepted 15 January 1998)     

The role of Asn14 in the stability and conformation of the reactive-site loop of winged bean chymotrypsin inhibitor: crystal structures of two point mutants Asn14-->Lys and Asn14-->Asp.

A double-headed chymotrypsin inhibitor, WCI, from winged bean seeds was cloned for structural and biochemical studies. The inhibitor was subjected to two point mutations at a conserved position, Asn14. This residue, known to have a pivotal role in stabilizing the first reactive-site loop (Gln63-Phe68) of the inhibitor, is highly conserved in the sequences of the other members of Kunitz (STI) family as well as in the sequences of Kazal family of serine protease inhibitors. The mutants, N14K and N14D, were subjected to biochemical assay and their characteristics were compared with those of the recombinant inhibitor (rWCI). Crystallographic studies of the recombinant and the mutant proteins are discussed. These studies were primarily aimed at understanding the importance of the protein scaffolding towards the conformational rigidity of the reactive-site loop. Our analysis reveals that, as the Lys14 side chain takes an unusual fold in N14K and the Asp14 side chain in N14D interacts with the loop residues by water-mediated hydrogen bonds, the canonical conformation of the loop has remained effectively intact in both the mutant structures. However, minor alterations such as a 2-fold increase in the inhibitory affinity towards the cognate enzyme were observed.     

Two-dimensional crystallization of bovine rhodopsin

Bovine rhodopsin has been clustered into two-dimensional crystals in highly purified native rod disk membranes and studied with negative staining and transmission electron microscopy. The lattice is P2(1) with dimensions of 8.3 X 7.9 nm and interaxis angles of 86 +/- 3 degrees. 110 images of ordered areas were digitized and aligned with computer-correlation methods to calculate an average image with diffraction to the fourth order. The images were computer-filtered and reconstructed to approx. 2 nm resolution. When crystals appeared they covered 20-40% of the surface of the preparation and, since rhodopsin is at least 95% of the protein, there is no doubt that the crystals were due to rhodopsin. There appear to be two rhodopsin dimers per unit cell. Each rhodopsin molecules takes up about 7.5 nm2 of membrane area and is estimated to be associated with about 12 lipids on each side of the membrane. The membrane area found for bovine rhodopsin supports the rhodopsin origin of rarely seen but more highly ordered two-dimensional crystals found in detergent-treated frog rod membranes (Corless, J.M., McCaslin, D.R. and Scott, B.L. (1982) Proc. Natl. Acad. Sci. USA 79, 1116-1120). Furthermore, the rhodopsin membrane area is close to that of bacteriorhodopsin and is consistent with a seven transmembrane helix structure proposed for rhodopsin (for references see Dratz, E.A. and Hargrave, D.A. (1983) Trends Biochem. Sci. 8, 128-131). Crystallization was accomplished by lowering the pH to 5.5 near the isoelectric point of rhodopsin, raising the salt concentration of 2 M (NH4)2SO4, adding 5% glucose and 0.02% Hibitane (Ayerst), a cationic amphipathic antiseptic that favored crystal growth.