Symmetries of the Boundary of AdS_5 x S^5 and Harmonic Superspace
  We study the boundary limit of the bulk isometries of AdS x S. The superconformal symmetry is realized on the coordinates of the AdS boundary, the fermionic superspace coordinates, and the harmonics on the sphere. We show how these may be related to the coordinates of an off-shell harmonic superspace of SCFT living on the boundary. In the special case of d=4, N=2 super Yang-Mills theory, a truncation of the N=4 SYM dual to Type IIB string theory compactified on AdS_5 x S^5, we identify the bosonic space SU(2)/U(1) of the N=2 harmonic superspace (known before as auxiliary) with the S^2 submanifold of the S^5. 
Piet Claus, Renata Kallosh, and J. Rahmfeld