Molecular and physiological role of the trehalose-hydrolyzing -glucosidase from Thermus thermophilus HB27

Centro de Neurociências e Biologia Celular, Departamento de Zoologia, Universidade de Coimbra, 3004-517 Coimbra, Portugal; Departamento de Bioquímica, Universidade de Coimbra, 3001-401 Coimbra, Portugal

^* To whom correspondence should be addressed. Email: numenius{at}cnc.uc.pt.

	Abstract

Trehalose supports growth of Thermus thermophilus strain HB27 but the absence of obvious genes for the hydrolysis of this disaccharide in the genome led us to search for enzymes for such purpose. We expressed a putative -glucosidase gene (TTC0107), characterized the recombinant enzyme and found that the preferred substrate was ,-1,1-trehalose, a new feature among -glucosidases. The enzyme could also hydrolyze the disaccharides kojibiose and sucrose (-1,2-linkage), nigerose and turanose (-1,3), leucrose (-1,5), isomaltose and palatinose (-1,6), and maltose (-1,4) to a lower extent. Trehalose was not, however, a substrate for the highly homologous -glucosidase from T. thermophilus strain GK24. The reciprocal replacement of a peptide containing 8 amino acids in the -glucosidases from strains HB27 (LGEHNLPP) and GK24 (EPTAYHTL) reduced the ability of the former to hydrolyse trehalose and provided trehalose-hydrolytic activity to the latter, showing that LGEHNLPP is necessary for trehalose recognition. Furthermore, disruption of the -glucosidase gene significantly affected growth of T. thermophilus HB27 in minimal medium supplemented with trehalose, isomaltose, sucrose or palatinose, to a lesser extent with maltose, but not with cellobiose (not a substrate for the -glucosidase), indicating that the -glucosidase is important for the assimilation of those four disaccharides, but is also implicated in maltose catabolism.