Identification of a novel α-galactosidase from the hyperthermophilic archaeon Sulfolobus solfataricus

Suffiblobus soffiataricus is an aerobic crenarchaeon that thrives in acidic volcanic pools. In this study, we have purified and characterized a thermostable et-galactosidase from cell extracts of S. soffataricus P2 grown on the trisaccharide raffinose. The enzyme, designated GaIS, is highly specific for alpha-linked galactosides, which are optimally hydrolyzed at pH 5 and 90 degrees C. The protein consists of 74.7-kDa subunits and has been identified as the gene product of open reading frame Sso3127. Its primary sequence is most related to plant enzymes of glycoside hydrolase family 36, which are involved in the synthesis and degradation of raffinose and stachyose. Both the galS gene from S. solfataricus P2 and an orthologous gene from Sulfolobus tokodaii have been cloned and functionally expressed in Escherichia coli, and their activity was confirmed. At present, these Suffolobus enzymes not only constitute a distinct type of thermostable alpha-galactosidases within glycoside hydrolase clan D but also represent the first members from the Archaea.