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Characterization of a maltodextrin glucosidase from Klebsiella variicola of the GH13_21 subfamily
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DOI：10.4025/actascitechnol.v48i1.73755.png)
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Abstract
En 中文
Klebsiella variicola is a Gram-negative bacterium belonging to the Klebsiella pneumoniae species complex. It is frequently isolated from many plants, where it is involved in nitrogen fixation and growth. However, it has also been described as associated with disease in humans and animals. Escherichia coli and K. pneumoniae are related members of the Enterobacteriaceae family that metabolize maltose and maltodextrins. However, only isolates of the K. pneumoniae species complex metabolize starch. In E. coli, four enzymes metabolize maltodextrins, including a periplasmic alpha-amylase (MalS), a cytoplasmatic amylomaltase (MalQ), a maltodextrin phosphorylase (MalP), and a maltodextrin glucosidase (MalZ). Considering the medical and agricultural importance of K. variicola and to better understand its role in maltodextrin degradation, the malZ gene was cloned from an isolate of this species, and the coded protein was recombinantly expressed and characterized. The K. variicola MalZ protein sequence was 79% identical to the E. coli MalZ and is the fifth enzyme and second maltodextrin glucosidase characterized from the GH13_21 CAZy subfamily. Its modeled monomeric structure shows beta-stranded amino-and carboxyterminal domains and a catalytic domain with a (beta/alpha)(8)-barrel. The 70 kDa expressed enzyme could promote glucose release from maltoheptaose and other maltodextrins. The enzyme's optimum temperature was 30 degrees C. The K-M and V-max for maltoheptaose were 32.7 mM and 2.58 mu mol/min of glucose released, respectively. Considering the characteristics of degrading maltodextrins, the release of glucose from this substrate, and the high profit of recombinant expression, the enzyme expressed in this work could be used in the industrial degradation of starch as a saccharifying enzyme.
Keywords:
Maltodextrin glucosidase
Klebsiella variicola
Recombinant expression
MalZ
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