Enzymes Required for Maltodextrin Catabolism in Enterococcus faecalis Exhibit Novel Activities

Area of Science:

• Microbiology
• Biochemistry
• Enzymology

Background:

• Maltodextrins, composed of α-1,4 and α-1,6 linked glucosyl residues, are degraded by Enterococcus faecalis.
• Previous understanding of maltodextrin transport and phosphorylation in E. faecalis was limited, particularly for longer maltooligosaccharides.

Purpose of the Study:

• To identify and characterize enzymes responsible for maltodextrin catabolism in Enterococcus faecalis.
• To elucidate the specific roles of maltodextrin hydrolase (MmdH) and a novel α-1,6-specific maltodextrin hydrolase (GmdH) in maltooligosaccharide degradation.

Main Methods:

• Enzyme purification and characterization of MmdH and GmdH.
• Enzymatic assays to determine substrate specificity and product formation.
• Construction and analysis of gene inactivation mutants (mmdH and gmdH) to assess growth phenotypes on various maltooligosaccharides.

Main Results:

• MmdH catalyzes the initial catabolic step for α-1,4-linked maltooligosaccharides, producing maltose and glucose.
• MmdH exhibits relaxed specificity, also acting as a maltogenic α-1,6-glucosidase on isopanose.
• GmdH specifically degrades panose into glucose and maltose, and its inactivation prevents growth on panose.
• A third enzyme, MmgT, functions in glucosyl residue transfer (disproportionation) between maltooligosaccharides.

Conclusions:

• Two novel enzymes, MmdH and GmdH, are crucial for the breakdown of diverse maltooligosaccharides in E. faecalis.
• The identified enzymes reveal a complex maltodextrin degradation pathway involving both hydrolase and transferase activities.
• These findings suggest similar maltose degradation pathways may exist in other Firmicutes, including streptococci and lactobacilli.