QTY Code

These may be paired as: Glutamine (Q) vs Leucine (L); Threonine (T) vs Valine (V) and Isoleucine (I); and Tyrosine (Y) vs Phenylalanine (F).

[3][4] The QTY Code was specifically conceived to render G protein-coupled receptors (GPCRs) into a water-soluble form.

Despite substantial transmembrane domain changes, the QTY variants of GPCRs maintain stable structure and ligand binding activities.

The –OH group of threonine (T) and tyrosine (Y) can form 3 hydrogen bonds with 3 water molecules (2 H-acceptors and 1 H-donor).

The QTY Code is robust and straightforward: it is the simplest tool to carry out membrane protein design without sophisticated computer algorithms.

Shapes of the 20 natural amino acids as they appear in an experimental electron density map at 1.5 angstrom resolution.
Hydrogen bond interactions between water and the amino acids (Courtesy of Michael Skuhersky, MIT)
The QTY code and how it replaces L, V, I, and F with Q, T, and Y. (A) Crystallographic electronic density maps of the following amino acids: leucine (L), asparagine (N), glutamine (Q), isoleucine (I), valine (V), threonine (T), phenylalanine (F), and tyrosine (Y).
Illustration of the QTY Code.