Alboaggregin-B: a new platelet agonist that binds to platelet membrane glycoprotein Ib

A new protein, called alboaggregin-B (AL-B), has been isolated from Trimeresurus albolabris venom by ion-exchange chromatography. It agglutinated platelets without the need for Ca2+ or any other cofactor. The purified protein showed an apparent molecular mass on SDS-PAGE and gel filtration of about 23 kDa under nonreducing conditions. Ristocetin did not alter the binding of AL-B to platelets or affect AL-B-induced platelet agglutination. Agglutinating activity was not dependent on either proteolytic or lectin-like activity in AL-B. Binding analysis showed that AL-B bound to platelets with high affinity (Kd = 13.6 +/- 9.3 nM) at approximately 30,800 +/- 14,300 binding sites per platelet. AL-B inhibited the binding of labeled bovine von Willebrand factor (vWF) to platelets. Monoclonal antibodies against the 45-kDa N-terminal domain of platelet glycoprotein Ib inhibited the binding both of AL-B and of bovine vWF to platelets, and also inhibited platelet agglutination induced by AL-B and bovine vWF. Specific removal of the N-terminal domain of GPIb by treatment of the platelets with elastase or Serratia marcescens protease reduced the binding of labeled AL-B and bovine vWF to platelets and blocked platelet agglutination caused by both agonists. Monoclonal antibodies to glycoprotein IIb/IIIa, to bovine vWF, and to bovine serum albumin did not show any effect on the binding of AL-B to platelets. Our results indicate that the binding domain for AL-B on platelet GPIb is close to or identical with the one for vWF. This new protein may be a very useful tool for studying the interaction between platelets and vWF.

Identification of cysteine residues in lamb kidney (Na,K)-ATPase essential for ouabain binding

N-(1-Pyrene)maleimide is a hydrophobic, sulfhydryl-directed, chemical modification probe which, at a low concentration, inhibits the capacity of lamb kidney sodium- and potassium-activated adenosine triphosphatase [Na,K)-ATPase; EC 3.6.1.3) to bind ouabain. This inhibition is partially blocked by preincubation of the enzyme with ouabagenin, an aglycone derivative which can be used as a reversible protecting ligand for the ouabain binding site. The kinetics of inhibition are not first order, suggesting that there may be more than one site of labeling which is responsible for the inhibition of ouabain binding. Although earlier work (Kirley, T. L., Lane, L. K., and Wallick, E. T. (1986) J. Biol. Chem. 261, 4525-4528) indicates that the inhibition is accompanied by a loss in the number of binding sites rather than a decrease in affinity of the sites for the ligand, other data (Scheiner-Bobis, G., Zimmerman, M., Kirch, V., and Schoner, W. (1987) Eur. J. Biochem. 165, 653-656) indicates that there is no cysteine residue located extracellularly in the ouabain binding site. By sequence analysis of alpha subunit peptides labeled by N-(1-pyrene)maleimide in the absence but not in the presence of protecting ligand, it is demonstrated in this work that there are two major sites of labeling protected by the binding of ouabagenin, Cys-367 and Cys-656. Both of these sites are located in the large cytoplasmic domain of the alpha subunit, one close to the phosphorylation site (Asp-369), and the other implicated in the binding of ATP (Cys-656). Therefore, it appears from this data that the inhibition of ouabain binding by N-(1-pyrene)maleimide is not due to modification of a site in the binding pocket for cardiac glycosides, but rather to an allosteric effect, since cardiac glycoside binding is known to be dependent on the phosphorylation state of the enzyme. The dependence of inhibition on the presence of sodium, potassium, and ATP also is consistent with this interpretation. The work reported here thus explains the apparent paradox posed by the earlier data.

Environmental factors and Parkinson's disease: a case-control study in China

We studied the role of environment in the development of Parkinson's disease (PD) in China, where industrialization is relatively recent and the population geographically stable. Using a case-control method, we investigated the relationship between PD and exposure to the following factors before disease onset: place of residence, source of drinking water, environmental and occupational exposure to various agricultural and industrial processes. Occupational or residential exposure to industrial chemicals, printing plants, or quarries was associated with an increased risk of developing PD. In contrast, living in villages and exposure to the common accompaniments of village life, wheat growing and pig raising, were associated with a decreased risk for PD. PD cases and controls did not differ with respect to other factors investigated. These findings are consistent with the hypothesis that environmental exposure to certain industrial chemicals may be related to the development of PD.