Chimeric protein of CD8a extracellular domain and CD4 transmembrane and cytoplasmic domain binds more efficiently to p56lck than CD8a

Abstract

p56^ick (Ick), a cytoplasmic protein tyrosine kinase of the src family, is non‐covalently associated with the cell surface coreceptors CD4 and CD8, which are expressed on thymocytes and mature T cells. The coreceptor protein plays an important role during the differentiation of thymocytes and the activation of T cells. DNA constructs were designed to study the roles of CD4 and CD8 during the differentiation of thymocytes. One is a chimeric cDNA which consists of coding regions for the extracellular domain of CD8a and the transmembrane and cytoplasmic domain of CD4. The other is the same chimeric cDNA but with a point mutation converting Cys to Ala in the Ick‐binding site to disrupt the association. We confirmed that the CD8a/CD4 chimeric molecule bound to Ick more efficiently than the wild type CDSa protein. However, the chimeric protein with the Cys ?Ala mutation did not associate with Ick. The results suggest a possibility that the CD8a/CD4 chimeric protein may behave like a CD4 protein in associating with Ick and that it may deliver a signal inside the cell in a similar manner. Analysing effects of the mutant CD8a/CD4 chimeric protein expression in developing thymocytes will elucidate the role of Ick during the determination of CD4/CD8 cell lineages.

Key words:

• CD8Q/CD4
• Lck binding
• Point mutation

Notes

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