Neurotoxic Phospholipases A2 Ammodytoxin and Crotoxin Bind to Distinct High-Affinity Protein Acceptors in Torpedo marmorata Electric Organ
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- 作者：Igor Kri
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- 刊名：Biochemistry
- 出版年：1997
- 出版时间：March 11, 1997
- 年：1997
- 卷：36
- 期：10
- 页码：2779 - 2787
- 全文大小：310K
- 年卷期：v.36,no.10(March 11, 1997)
- ISSN：1520-4995
文摘
We studied the binding of radioiodinated ammodytoxin C, amonomeric phospholipase A2neurotoxin from Vipera ammodytes, and ofradioiodinated crotoxin, a dimeric phospholipase A2neurotoxinfrom Crotalus durissus terrificus, to presynapticmembranes from the electric organ of Torpedomarmorata.In both cases, two different families of specific binding siteswere identified and characterized. Thehigh-affinity binding sites for both toxins have been shown to beproteins. The low-affinity binding siteswere not affected by proteinases or heat, suggesting the involvement ofcertain lipid structures in thistype of binding. By affinity-labeling,[125I]ammodytoxin C was shown to be associatedpredominantlywith membrane proteins of apparent molecular masses of 70 000 and20 000 Da and to a lesser extentwith several proteins of apparent molecular masses ranging between39 000 and 57 000 Da.[125I]crotoxin,on the other hand bound primarily to a 48 000 Da membrane protein.All phospholipases A2 tested,except 
-bungarotoxin, inhibited the low-affinity specific binding ofammodytoxin C, whereas onlyneurotoxic phospholipases A2 prevented the high-affinitybinding and the cross-linking of ammodytoxinC and crotoxin. The inhibition profiles of high-affinity bindingfor [125I]crotoxin and for[125I]ammodytoxinC were quite different. Ammodytoxin C and crotoxin did not inhibiteach other on their respective high-affinity binding sites. These observations indicate that at leasthigh-affinity binding sites of these twotoxins are different. In contrast with crotoxin, the isolatedbasic subunit CB of crotoxin was able tocompletely inhibit the high-affinity binding of[125I]ammodytoxin C. Therefore, the acidicsubunit CA ofcrotoxin does not simply act as a chaperone for CB subunit,but it also confers a distinct binding specificityto the crotoxin.
-bungarotoxin, inhibited the low-affinity specific binding ofammodytoxin C, whereas onlyneurotoxic phospholipases A2 prevented the high-affinitybinding and the cross-linking of ammodytoxinC and crotoxin. The inhibition profiles of high-affinity bindingfor [125I]crotoxin and for[125I]ammodytoxinC were quite different. Ammodytoxin C and crotoxin did not inhibiteach other on their respective high-affinity binding sites. These observations indicate that at leasthigh-affinity binding sites of these twotoxins are different. In contrast with crotoxin, the isolatedbasic subunit CB of crotoxin was able tocompletely inhibit the high-affinity binding of[125I]ammodytoxin C. Therefore, the acidicsubunit CA ofcrotoxin does not simply act as a chaperone for CB subunit,but it also confers a distinct binding specificityto the crotoxin.