Biomedical subjects
M T Villar
Publications and source records attributed to M T Villar.
Autosomal dominant polycystic kidney disease complicated by glomerulonephritis.
Two patients with autosomal dominant polycystic kidney disease (ADPKD) and concurrent glomerulonephritis are described. Both developed nephrotic-range proteinuria and one showed a concomitant acceleration in the rate of decline of renal function. Subsequent open renal biopsy revealed membrano-proliferative type-1 and mesangio-proliferative glomerulonephritis, respectively. Nephrotic-range proteinuria in the presence of ADPKD, with or without an accompanying decline in renal function, should prompt further investigation to exclude coexisting glomerular disease.
Cloning, expression, isolation and characterization of the pre-S domains of hepatitis B surface antigen, devoid of the S protein.
The 'pre-S' parts of the envelope protein of hepatitis B virus (HBV) have been proposed to be involved in the infection of hepatocytes by HBV. In order to facilitate the study of these processes, we have developed an expression system to allow the production and purification of large quantities of the pre-S protein. To obtain a protein containing all of the pre-S sequence and only this sequence, mutations were introduced into the HBV(ayw) genome to create an NdeI restriction site at the initial ATG of the large surface protein gene. Also, stop codons and a BglII restriction site were introduced after the last codon of pre-S2. This fragment was then cloned into the high-expression vector pET-3A. A protein of the expected Mr was expressed at a level of up to 10% of the total soluble protein in HMS174 (DE3) cells, as judged by SDS/PAGE. A rapid purification method has been developed for this protein. The protein retains the polyalbumin-binding activity ascribed to the pre-S2 sequence, and is recognized by both polyclonal and monoclonal antibodies directed against pre-S determinants. Gel filtration chromatography demonstrates that the protein is monomeric and globular, and c.d. spectroscopy indicates that beta-sheet is the major periodic structure.
Recurrent and fatal haemoptysis caused by an atheromatous abdominal aortic aneurysm.
A 74 year old woman presented with a two month history of recurrent small hemoptyses and died after a subsequent massive haemoptysis. At postmortem examination the source of bleeding was found to be a leaking saccular, atheromatous abdominal aortic aneurysm, which had ruptured through the diaphragm into the lower lobe of the right lung.
[Metal ions in the insulin-receptor interaction in human erythrocytes].
The kinetics of insulin binding to its receptors on human erythrocytes suggests the existence of two types of receptors exhibiting negative cooperativity upon the binding of the hormone. Solubilized and purified receptors were associated to Zn++ or Cu++. The addition of these ions to erythrocytes or to purified insulin receptors from human erythrocytes resulted in an increase of specific insulin binding. Dialysis of solubilized or purified receptors against chelating agents such as EDTA or 1, 10-phenanthroline resulted in a decrease in specific binding of insulin. With the readdition of Zn++ or Cu++ to the medium an increase in specific binding was observed, and values much higher than those of the original preparations were obtained. Dialysis of purified receptors against chelating agents resulted in a decrease in the content of Zn++ and Cu++. These results suggest the possible involvement of a metal ion associated to the receptor in the formation of the insulin-receptor complex.
Phospholipase A2 hydrolysis of membrane phospholipids causes structural alteration of the nicotinic acetylcholine receptor.
Thermal perturbation techniques have been used to probe structural alteration of the nicotinic acetylcholine receptor as a function of perturbations of its native membrane environment. Differential scanning calorimetry and a technique involving heat inactivation of the alpha-bungarotoxin-binding sites on the receptor protein reveal that there is a profound destabilization of the acetylcholine receptor structure when receptor-containing membranes are exposed to phospholipase A2. The characteristic calorimetric transition assigned to irreversible denaturation of the receptor protein and the heat inactivation profile of alpha-bungarotoxin-binding sites are shifted to lower temperatures by approx. 7 and 5 C degrees, respectively, upon exposure to phospholipase A2 at a phospholipase/neurotoxin binding site molar ratio of about 1:100. The effects of phospholipase A2 on receptor structure can be (i) reversed by using bovine serum albumin as a scavenger of phospholipase hydrolysis products of membrane phospholipids, and (ii) stimulated by incorporation into the membranes of free, polyunsaturated fatty acids. In particular, linolenic acid (18:3(n-3] causes detectable destabilization of the alpha-bungarotoxin binding sites on the receptor at free fatty acid/receptor molar ratios as low as 10:1. Furthermore, alteration of receptor structure by added phospholipase occurs very rapidly, which is consistent with the observation of rapid in situ phospholipase A2 hydrolysis of membrane phospholipids, particularly highly unsaturated phosphatidylethanolamine and phosphatidylserine. Based on previously published data on the inhibition of acetylcholine receptor cation-gating activity caused by the presence of either phospholipase A2 or free fatty acids (Andreasen T.J. and McNamee M.G. (1980) Biochemistry 19, 4719), we interpret our data as indicative of a correlation between structural and functional alterations of the membrane-bound acetylcholine receptor induced by phospholipase A2 hydrolysis products.
Thermal perturbation studies of membrane-bound acetylcholine receptor from Torpedo: effects of cholinergic ligands and membrane perturbants.
Thermal perturbation techniques have been used to probe structural features of the nicotinic acetylcholine receptor (AcChR). The information obtained from differential scanning calorimetry (DSC) of AcChR membranes (M.C. Farach and M. Martinez-Carrion (1983) J. Biol. Chem. 258, 4176) in the absence and in the presence of cholinergic ligands and local anesthetics, is comparable to that obtained from a simpler technique of heat inactivation of the alpha-bungarotoxin (alpha-Bgt) binding sites on the AcChR protein in similar samples. When AcChR membranes are heated at approximately 1 degree C/min, heat inactivation of toxin binding sites has a characteristic T50 value (temperature at which 50% of the initial capacity to bind alpha-Bgt remains) of approximately 60 degrees C. When heated at a constant temperature during increasing periods of time, the rate at which heat inactivation occurs is also characteristic of the temperature chosen for the experiment. The above thermal parameters are also sensitive to perturbation of the AcChR membrane matrix by the presence of subsolubilizing concentrations of detergents. Moreover, elimination of detergents by dialysis allows us to evaluate the reversibility or irreversibility of AcChR thermal destabilization induced by detergents or other membrane perturbants. Under the experimental conditions used, structural destabilization induced by octylglucoside or cholate can be fully reversed by detergent dialysis, while that exerted by deoxycholate cannot. "Thermal gel" analysis of the aggregation of AcChR subunits induced by heat (G. Soler, J. R. Mattingly, and M. Martinez-Carrion (1984) Biochemistry 23, 4630) has also been used to assess the effects of detergent presence on the AcChR protein. When deoxycholate is used as the perturbing agent, there is a particularly effective sulfhydryl-mediated aggregation of the gamma-delta subunit group, which appears to correlate with the irreversible destabilization of alpha-Bgt binding sites induced by that detergent.