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Contribution of AmyA, an extracellular α‐glucan degrading enzyme, to group A streptococcal host–pathogen interaction
Author(s) -
Shelburne III Samuel A.,
Keith David B.,
Davenport Michael T.,
Beres Stephen B.,
Carroll Ronan K.,
Musser James M.
Publication year - 2009
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2009.06858.x
Subject(s) - biology , extracellular , microbiology and biotechnology , pathogen , streptococcus pyogenes , glucan , enzyme , saliva , virulence , polysaccharide , streptococcus , biochemistry , bacteria , gene , genetics , staphylococcus aureus
Summary α‐Glucans such as starch and glycogen are abundant in the human oropharynx, the main site of group A Streptococcus (GAS) infection. However, the role in pathogenesis of GAS extracellular α‐glucan binding and degrading enzymes is unknown. The serotype M1 GAS genome encodes two extracellular proteins putatively involved in α‐glucan binding and degradation; pulA encodes a cell wall anchored pullulanase and amyA encodes a freely secreted putative cyclomaltodextrin α‐glucanotransferase. Genetic inactivation of amyA , but not pulA , abolished GAS α‐glucan degradation. The Δ amyA strain had a slower rate of translocation across human pharyngeal epithelial cells. Consistent with this finding, the Δ amyA strain was less virulent following mouse mucosal challenge. Recombinant AmyA degraded α‐glucans into β‐cyclomaltodextrins that reduced pharyngeal cell transepithelial resistance, providing a physiologic explanation for the observed transepithelial migration phenotype. Higher amyA transcript levels were present in serotype M1 GAS strains causing invasive infection compared with strains causing pharyngitis. GAS proliferation in a defined α‐glucan‐containing medium was dependent on the presence of human salivary α‐amylase. These data delineate the molecular mechanisms by which α‐glucan degradation contributes to GAS host–pathogen interaction, including how GAS uses human salivary α‐amylase for its own metabolic benefit.