H-1-NMR ANALYSIS OF CD3-EPSILON REVEALS THE PRESENCE OF TURN-HELIX STRUCTURES AROUND THE ITAM MOTIF IN AN OTHERWISE RANDOM COIL CYTOPLASMICTAIL

The conformation adopted in solution by the cytoplasmic tail of CD3-ep silon has been analyzed by H-1-nmr. The cytoplasmic mil is mostly rand om coil except for the amino acids conforming the immunoreceptor tyros ine-based activation motif (ITAM), Y xxL/IxxxxxxxY xxL. Although the N -terminal Y xxL sequence of the motif is poorly folded adopting 6-resi due aim-like conformations with the Tyr side chain in two different or ientations, the C-terminal Y xxxL sequence is placed in a more complex structure involving a set of nonclassical alpha-helix turns and beta- turns that comprises 11 amino acids. This structure is not modified by phosphorylation of the tyrosine residue. The differences in the confo rmation adopted around the two tyrosines of the ITAM motif suggest tha t they may play different roles pertaining to either binding signal tr ansducing proteins or, alternatively, proteins involved in other proce sses such as endoplasmic reticulum location. (C) 1997 John Wiley & Son s, Inc.