Primary structure and processing of the Candida tsukubaensis alpha-glucosidase. Homology with the rabbit intestinal sucrase-isomaltase complex and human lysosomal alpha-glucosidase

The nucleotide sequence of a 4.39-kb DNA fragment encoding the alpha-glucosidase gene of Candida tsukubaensis is reported. The cloned gene contains a major open reading frame (ORF 1) which encodes the alpha-glucosidase as a single precursor polypeptide of 1070 amino acids with a predicted molecular mass of 119 kDa. N-terminal amino acid sequence analysis of the individual subunits of the purified enzyme, expressed in the recombinant host Saccharomyces cerevisiae, confirmed that the alpha-glucosidase precursor is proteolytically processed by removal of an N-terminal signal peptide to yield the two peptide subunits 1 and 2, of molecular masses 63-65 kDa and 50-52 kDa, respectively. Both subunits are secreted by the heterologous host S. cerevisiae in a glycosylated form. Coincident with its efficient expression in the heterologous host, the C. tsukubaensis alpha-glucosidase gene contains many of the canonical features of highly expressed S. cerevisiae genes. There is considerable sequence similarity between C. tsukubaensis alpha-glucosidase, the rabbit sucrase-isomaltase complex (proSI) and human lysosomal acid alpha-glucosidase. The cloned DNA fragment from C. tsukubaensis contains a second open reading frame (ORF 2) which has the capacity to encode a polypeptide of 170 amino acids. The function and identity of the polypeptide encoded by ORF 2 is not known.

Molecular cloning and characterization of a Candida tsukubaensis alpha-glucosidase gene in the yeast Saccharomyces cerevisiae

The molecular cloning of an alpha-glucosidase gene isolated from a Candida tsukubaensis (CBS 6389) genomic library in Saccharomyces cervisiae is reported. The cloned gene is contained within a 6.2 kb Sau3A DNA fragment and directs the synthesis and secretion of an amylolytic enzyme into the extracellular medium of the recombinant host, S. cerevisiae. The cloned enzyme was found to have an unusually broad substrate specificity and is capable of hydrolysing alpha-1,2, alpha-1,3, alpha-1,4 and alpha-1,6 linked, as well as aryl and alkyl, D-glucosides. On the basis of its substrate specificity profile, the cloned enzyme was classified as an alpha-glucosidase (E.C. 3.2.1.20). It has a pH optimum in the range 4.2-4.6, a temperature optimum of 58 degrees C and is readily inactivated at pasteurization temperature (60 degrees C). Southern blot analysis failed to reveal any homology between the cloned gene and genomic DNA isolated from other well characterized amylolytic yeasts. A rapid plate-assay, based on the utilization of a chromogenic substrate X-alpha-D-glucoside to detect the expression of the cloned alpha-glucosidase in S. cerevisiae transformants, was developed.

Daily life therapy: a Japanese model for educating children with autism

The controversial practice of Daily Life Therapy, as demonstrated at the Boston Higashi School in Massachusetts, is reviewed. Five fundamental principles of Daily Life Therapy are examined: instruction that is group-oriented; routine activities that are highly structured; instructional techniques that center on learning through imitation; a method for reducing children's levels of unproductive activity through rigorous physical exercise; and a curriculum that focuses on movement, music, and art. These central features of Daily Life Therapy are discussed in light of current theory, research, and educational practices in autism. Empirical questions raised by this unique treatment mode are outlined.

Hyaluronic acid capsule: strategy for oxygen resistance in group A streptococci

Unencapsulated variants of encapsulated, M-protein-positive group A streptococci are oxygen sensitive and secrete inhibitory concentrations of hydrogen peroxide when grown in aerated broth cultures. The organisms were equally sensitive to hydrogen peroxide, and neither exhibited catalase or peroxidase activity, suggesting that differences in oxygen sensitivity reflect dissimilarity in oxygen uptake. The encapsulated parental culture was found to grow in aggregates that take up oxygen more slowly than unencapsulated, oxygen-sensitive derivatives. Moreover, the latter grow in an unaggregated, homogenous suspension. The enzyme hyaluronidase was able to disrupt aggregates of the encapsulated strain increase the rate that these cells take up oxygen, and cause the accumulation of toxic concentrations of hydrogen peroxide earlier in their growth cycle. The evidence presented shows that the aggregation of streptococcal cells by their hyaluronic acid capsule provides this organism with a novel means to avoid self-destruction by oxygen metabolites--cells are shielded from oxygen. The reduced surface-to-volume ratio and limited diffusion of oxygen into the interior of aggregates are proposed as the protective mechanism.