FIG. 1.

ClustalX alignment (29) of α-glucosidases from T. thermophilus strains HB27, HB8, and GK24 with homologous proteins from Bacillus species. The boxes represent the seven CRs of the α-amylase family. The boldface amino acids indicate putative catalytic and substrate-binding residues, and the underlined portions indicate an eight-amino-acid sequence, which is the target sequence for mutagenesis, that is identical in the α-glucosidases of strains GK24 and HB8 but different in the HB27 α-glucosidase. Gray shading, putative catalytic aspartates and glutamate; black shading, putative functional histidines (substrate-binding sites); arrow, Ca²⁺-binding aspartate; star, conserved identical amino acids; colon, conservative substitutions; period, semiconservative substitutions; T. thHB27, T. thermophilus HB27 (NCBI accession number YP_004082); T. thHB8, T. thermophilus HB8 (NCBI accession number YP_143747); T. thGK24, T. thermophilus GK24 (EMBL accession number AAD50603); B. SAM1606, Bacillus sp. strain SAM1606 (EMBL accession number CAA54266); B. cereus, Bacillus cereus ATCC 7064 (EMBL accession number CAA37583).