Distinct conformations of Ly49 natural killer cell receptors mediate MHC class I recognition in trans and cis

BACK J, MALCHIODI EL, CHO S, SCARPELLINO L, SCHNEIDER P, KERZIC MC, MARIUZZA RA, HELD W

IMMUNITY

CELL PRESS

Año: 2009 vol. 31 p. 598 - 608

1074-7613

Certain cell surface receptors engage ligands expressed on juxtaposed cells, but also ligands on the same cell. The structural basis for trans versus cis binding is not known. Here, we show that Ly49 NK cell receptors bind two MHC-I molecules in trans when the two ligand-binding domains are back-folded onto the long stalk region. In contrast, dissociation of the ligand-binding domains from the stalk and their reorientation relative to the NK cell membrane allow monovalent binding of MHC-I in cis. These distinct conformations (back-folded and extended) explain the divergent functional consequences of cis versus trans interactions, define the structural basis for cis–trans binding by Ly49 receptors, and identify the stalk region as an essential element for receptor function.