STRUCTURE AND FUNCTION OF PROTEINS OF THE PHOSPHOTRANSFERASE SYSTEM AND OF 6-PHOSPHO-BETA-GLYCOSIDASES IN GRAM-POSITIVE BACTERIA

New information about the proteins of the phosphotransferase system (P TS) and of phosphoglycosidases of homofermentative lactic acid bacteri a and related species is presented. Tertiary structures were elucidate d from soluble PTS components. They help to understand regulatory proc esses and PTS function in lactic acid bacteria. A tertiary structure o f a membrane-bound enzyme II is still not available, but expression of Gram-positive genes encoding enzymes 11 can be achieved in Escherichi a coli and enables the development of effective isolation procedures w hich are necessary for crystallization experiments. Considerable progr ess was made in analysing the functions of structural genes which are in close vicinity of the genes encoding the sugar-specific PTS compone nts, such as the genes encoding the tagatose-6-P pathway and the 6-pho spho-beta-glycosidases. These phosphoglycosidases belong to a subfamil y of the beta-glycosidase family I among about 300 different glycosida ses. The active site nucleophile was recently identified to be Glu 358 in Agrobacterium beta-glucosidase. This corresponds to Glu 375 in sta phylococcal and lactococcal 6-phospho-beta-galactosidase. This enzyme is inactivated by mutating Glu 375 to Gln. Diffracting crystals of the lactococcal 6-P-beta-galactosidase allow the elucidation of its terti ary structure which helps to derive the structures for the entire glyc osidase family 1. In addition, a fusion protein with 6-phospho-beta-ga lactosidase and staphylococcal protein A was constructed.