A Sialidase-Susceptible Ganglioside, IV3α(NeuGcα2-8NeuGc)-Gg4Cer, Is a Major Disialoganglioside in WHT/Ht Mouse Thymoma and Thymocytes1

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Abstract
The disialogangliosides of WHT/Ht mouse thymomas, which were obtained by subcutaneous transplantation of a thymoma that developed spontaneously in a WHT/Ht mouse, were purified and characterized. From the results of sugar-composition analysis, a permethylation study, enzymatic hydrolysis followed by TLC-immunostaining, negativeion fast atom bombardment mass spectrometry (FAB/MS), and 1H-NMR spectroscopy, the structure of one of the five purified disialogangliosides was determined to be IV3α(NeuGcα2-8NeuGc)-Gg4Cer. The other 4 disialogangliosides were tentatively characterized on the basis of sialidase treatment followed by TLC-immunostaining with cholera toxin B subunit and anti-Gg4Cer antibody to be IV3α(NeuGca-NeuGc)-Gg4Cer, IVa(NeuGca-NeuAc)-GgHCer, IVαNeuAc,II3aNeuAc-Gg4Cer, and IVαNeuGc.II3aNeuGc-Gg4Cer. In addition, another component exhibiting one spot on TLC was a mixture of IVαNeuGcII3aNeuAc-Gg4Cer and IVαNeuAc,II3aNeuGc-Gg4Cer. Then the occurrence of these gangliosides in WHT/Ht mouse thymocytes was examined. As one of two major disialogangliosides, the thymocytes contained IV3a(NeuGcα2-8NeuGc)-Gg4Cer, which was characterized with a mass spectrum and mass chromatograms obtained by micro high-performance liquid chromatography-FAB/MS. The other major disialoganglioside was tentatively characterized to be II3α-(NeuGca-NeuGc)-Gg4Cer by sialidase treatment followed by TLC-immunostaining. A sialidase-susceptible monosialoganglioside, IV3 αNeuGc-Gg4 [GMlb(NeuGc)], had been reported to be characteristic of mouse immune tissues [Nakamura,K. et al. (1988) J. Biochem 103, 201–208]. Taken together, the results suggest that the pathway from Gg4Cer to IV3α(NeuGca2-8NeuGc)-Gg4Cer through GMlb(NeuGc) is quite active in mouse immune tissues. 1 This work was supported in part by a Grant-in-Aid for Scientific Research on Priority Areas, No. 02259106 and 02206103, from the Ministry of Education, Science and Culture of Japan and a grant from the Mitsubishi Foundation.

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