A Rare Double Pathology- Coexistent Large Cell Neuroendocrine Cell Carcinoma of the Lung with Basal Cell Carcinoma of the Skin

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Human carbonic anhydrase I: Effect of specific site mutations on its function.

Carbonic anhydrase I (CAI) is one out of ten CA isoenzymes that have been identified in humans. X-ray crystallographic and inhibitor complex studies of human carbonic anhydrase I (HCAI) and related studies in other CA isoenzymes identified several residues, in particular Thr199, GlulO6, Tyr7, Glull7, HislO7, with likely involvement in the catalytic activity of HCAI. To further study the role of these residues, we undertook, site-directed mutagenesis of HCAI. Using a polymerase chain reaction based strategy and altered oligonucleotide primers, we modified a cloned wild type hCAI gene so as to produce mutant genes encoding proteins with single amino acid substitutions. Thrl99Val, Thrl99Cys, Thr199Ser, GlulO6Ile, GlulO6Gln, Tyr7Trp, Glu.117Gln, and His I 07Val mutations were thus generated and the activity of each measured by ester hydrolysis. Overproduction of the Glu 117Gln and His I 07Val mutant proteins in Escherichia coli resulted in a large proportion of the enzyme forming aggregates probably due to folding defect. The mutations Thr199Val, GlulO6Ile and GlulO6Gln gave soluble protein with drastically reduced enzyme activity, while the Tyr7Trp mutation had only marginal effect on the activity, thus s.uggesting important roles for Thr199 and GlulO6 but not for Tyr7 in the catalytic function of HCAI.

Drug protein interaction at the molecular level: A study of sulphonamide carbonic anhydrase complexes.

The molecular mechanism of drug action has been studied by X-ray diffraction analysis of human carbonic anhydrase I complexed with two different sulphonamides. The acetazolamide and amino benzene sulphonamide are found to bind to the catalytically essential zinc ion thereby inhibiting the function of the enzyme. The inhibitor molecules are stabilized in the active site of the protein by van der Waals interaction with a number of protein side chain groups.

Structure of presynaptic toxins: Crystallization and preliminary x-ray diffraction data on Notechis II-5, a presynaptic toxin phospholipase.

The presynaptic neutrotoxin-phospholipase, Notechis II-5 from the venom of Notechis Scutatus scutatus (Australian tiger snake) has been crystallized in a form suited for xray diffraction analysis. The crystals belong to the orthorhombic space group P21 21,21, with unit cell dimensions, a=146.1, b =43.5 and c=39.0 A. There are two molecules of Notechis II- 5 in the asymmetric unit. The molecular weight is about 13,500. Notechis II-5 is highly homologous to Notexin, another presynaptic toxin from the venom of the Australian tiger snake, to bovine and porcine pancreatic phospholipases A and other venom phospholipases.