Identification of a new subfamily of sulphotransferases: cloning and characterization of canine SULT1D1

Sulphation is an important conjugation pathway in drug metabolism that has been studied in several species including humans. However, few studies have been performed using the dog as a subject. In this report we describe the cloning and characterization of a canine cytosolic sulphotransferase (SULT). The overall primary structure of this enzyme is very similar to that of a rat phenol-sulphating enzyme found in the EMBL Database and to a mouse SULT termed amine-N-sulphotransferase (81% identity). The expressed canine SULT conjugates small phenols and aromatic amines such as dopamine, minoxidil, p-nitrophenol and 5-hydroxytryptamine, but not dehydroepiandrosterone or β-oestradiol. These results are in agreement with the results reported for the mouse SULT. In contrast with the mouse enzyme, the canine SULT does not conjugate eicosanoid compounds, i.e. prostaglandins, thromboxane B2 or leukotriene E4. The canine SULT is expressed at high levels in the colon of both genders; it is also expressed in the small intestine, kidney and liver. Furthermore, because the canine, mouse and rat SULT forms exhibit significant sequence identity (more than 80%), they seem to represent a distinct group in the SULT family tree. This suggestion is strengthened by the low identity with other SULTs. The subfamily that is most similar to this new group is SULT1A, with approx. 60% similarity. However, the mouse and canine enzymes are not characterized by the efficient sulphation of p-nitrophenol, dopamine, β-oestradiol or oestrone. Thus these results seem to exclude them from the SULT1A subfamily. We therefore propose a new subfamily in the phenol SULT family, designated SULT1D, and consequently the canine enzyme is termed SULT1D1.