Figure 3.

TULA-2 substrate specificity determinants. (A) Class I N-terminal motif is defined by a proline residue at position pY-1. It also requires the presence of one or two aromatic residues and the exclusion of basic residues at certain positions. Preference (green) or aversion (red) of various types of amino acid residues at specific positions is shown by the letter case: strong and weaker preference/aversion are indicated as uppercase and lowercase, respectively. Class II N-terminal motif shows a strong preference for aromatic residues at positions pY-5 and pY-4, and acidic residues at pY-3 and pY-2. Positions pY-3 and pY-2 also show some preference for aromatic residues. Also, a very strong aversion to basic residues for the entire length of the analyzed sequence is seen in class II. C-terminal substrate sequences show a strong preference for aromatic and acidic residues, but no clear consensus motif is recognized there. (B) Sequences of the major regulatory pY-sites of mouse Syk and ZAP-70 are presented. Homologies between the two PTKs are denoted by uppercase. Positive and negatives substrate specificity determinants are indicated in green and red, respectively. The specificity constants (k_cat/K_m) for these substrate sites, determined in Refs. [35,49], are indicated. ND = not determined.