Fig. 3. Identification of critical amino acids for epimorphin secretion. (A) Comparison of the sequences close to the cleavage site of epimorphin (Epm) and conserved syntaxin family members. Syntaxin 1A, syn1; syntaxin 3 (NM001025307), Syn3; and syntaxin 4 (NP033320), Syn4. Histidine H246 (red) is conserved in epimorphin from mouse (m, D10475), human (h, D14582), quail (q, AB076670) and sheep (s, E32546); other syntaxins have arginine R246 (blue). Adjacent to H246, the KEE sequence (red-yellow-red) is also conserved in epimorphin, whereas the VXD sequence (blue-black-blue) occupies this position in syntaxin 1A and syntaxin 3. (B) H246 is crucial for processing and secretion of epimorphin. The H246R mutation (CATAGG) in the T7-epimorphin sequence dramatically suppressed the secretion of 30 kDa epimorphin. The R246H (AGGCAT) mutation in T7-syntaxin-1A resulted in the secretion of a 30 kDa form.