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pMNEI, a single chain sweet protein ~'¢lat~ to monellin, has been studied by means of ~H NMR at 500 MHz. A partial sequential assignment performed by means of the MCD method allowed the determination of the secondary structure of a large portion of theft-sheet of pMNEI that contains a likely 'sweet finger': the loop connecting the fl-strands from residue 59 to residue 78, corresponding to segment 16--35 of the A chain of monellin. The detailed three-dimensional structure of the loop (Tyr~.Ala6LSer~.A~p~), determined from several interresida¢ and intraresidue NOEs and subsequent energy minimization, shows that the side chains of Tyr ~ and Asp ~9 tit our model of the sweet receptor in a manner very similar to that of the side chains of Ph¢ and Asp of aspartmne.

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The cytosolic tail of the major histocompatibility complex-associated invariant chain protein contains two Leu-based motifs that both mediate efficient sorting to the endocytic pathway. Nuclear magnetic resonance data on a peptide of 27 residues corresponding to the cytosolic tail of human invariant chain indicate that in water at pH 7.4 the membrane distal motif Leu