FIGURE 5.
Structural classification of Ly49 NK receptors. A, structure-based sequence alignment of the MHC-binding regions of Ly49 NKDs. Secondary structure elements for Ly49C and Ly49A are denoted by loops (α-helices) and arrows (β-strands). These, and the loop regions, are numbered according to Fig. 1. The classification into group I or II is based on the known, or predicted, presence (I) or absence (II) of helix α3 within loop L3. The classification into subgroups (Ia, Ib; IIa, IIb), and into group III or IV, is based on the dendrogram in B. White characters on a red background show MHC-contacting residues that are strictly, or mostly, conserved in group I or II, based on the Ly49C-H-2Kb or Ly49A-H-2Dd structure. MHC-contacting residues that differ are drawn in white and framed in blue. The remaining residues are black. Sequences were retrieved from GenBank™ or SwissProt using the following accession numbers: Ly49A, M25812; Ly49I, AF237686; Ly49B, U10304; Ly49C, U56404; Ly49D, L78247; Ly49E, Q60652; Ly49F, Q60653; Ly49G, S78689; Ly49H, U12889; Ly49L, AF213453; Ly49M, AF028134; Ly49O, AF146571; Ly49P, AF146570; Ly49R, AF288377; Ly49S, AF288378; Ly49T, AF288379; Ly49U, AF288380; Ly49V, AF288380; Ly49W, AF283250. Ly49K and Ly49N were not included because only partial sequences are available. B, dendrogram of Ly49 NK receptors. The sequences of the 21 Ly49 NKDs in A, corresponding to residues 136-262, were aligned and a dendrogram was generated using ClustalW 1.83.