Fig. 2.

Specific compounds allow uncoupling of transport, ubiquitination, endocytosis and signaling in the Gap1 transceptor. a The uptake of an amino acid triggers a (series of) conformational changes, of which one allows the ubiquitination of Gap1. Ubiquitination and an additional conformational change are required to trigger endocytosis of Gap1. Signaling to PKA is triggered by an independent conformational event. b The dipeptide l-Leu-Gly is not transported but is able to trigger all subsequent events like a regular amino acid. c The dipeptide l-Asp-γ-Phe is also not transported but is only able to trigger the conformation that allows ubiquitination. d l-Lysine is transported but is not able to trigger signaling nor endocytosis. However, it can also induce the conformation that elicits ubiquitination. e l-histidine cannot trigger signaling but can induce the whole endocytic internalization process just like a regular amino acid