INHIBITION OF THE INTERACTION BETWEEN TYROSINE-BASED MOTIFS AND THE MEDIUM-CHAIN SUBUNIT OF THE AP-2 ADAPTER COMPLEX BY SPECIFIC TYRPHOSTINS

Several intracellular membrane trafficking events are mediated by tyro sine-containing motifs found within the cytosolic domains of certain i ntegral membrane proteins. Many of these tyrosine motifs conform to th e consensus YXX Phi, (where Phi represents a bulky hydrophobic residue ). This YXX Phi motif has been shown to interact with the medium chain subunits of adaptor complexes that generally link. relevant integral membrane protein cytosolic domains to the clathrin coat involved in ve sicle formation. The motif YXX Phi, is also very similar to motifs tha t are targets for phosphorylation by tyrosine kinases. Tyrosine kinase inhibitors known as tyrphostins are structural analogues of tyrosine, and so it is possible that tyrphostins could also inhibit interaction s between medium chains and YXX Phi, motifs. TGN38 is a type I integra l membrane protein containing a tyrosine motif, YQRL, within the cytos olic domain. We have previously shown that this motif interacts direct ly with the medium chain subunit of the plasma membrane localized AP-2 adaptor complex (mu 2) We have investigated a range of tyrphostins an d demonstrated a specific inhibition of the interaction between mu 2 a nd the TGN38 cytosolic domain by tyrphostin A23 through in vitro analy sis and the yeast two-hybrid system. These data raise the exciting pos sibility that different membrane traffic events could be inhibited by specific tyrphostins.