The authors note that due to a printer's error, on page 4460, Fig. 2 appears incorrectly in part. The middle and bottom panels were transposed. The corrected figure and its legend appear below. MGAS5005∆ccpA comp∆ccpA

Historically, the study of bacterial catabolism of complex carbohydrates has contributed to understanding basic bacterial physiology. Recently, however, genome-wide screens of streptococcal pathogenesis have identified genes encoding proteins involved in complex carbohydrate catabolism as participating in pathogen infectivity. Subsequent studies have focused on specific mechanisms by which carbohydrate utilization proteins might contribute to the ability of streptococci to colonize and infect the host. Moreover, transcriptome and biochemical analyses have uncovered novel regulatory pathways by which streptococci link environmental carbohydrate availability to virulence factor production. Herein we review new insights into the role of complex carbohydrates in streptococcal host-pathogen interaction.

SummaryWe previously demonstrated that the cell-surface lipoprotein MalE contributes to GAS maltose/ maltodextrin utilization, but MalE inactivation does not completely abrogate GAS catabolism of maltose or maltotriose. Using a genome-wide approach, we identified the GAS phosphotransferase system (PTS) responsible for non-MalE maltose/maltotriose transport. This PTS is encoded by an open reading frame (M5005_spy1692) previously annotated as ptsG based on homology with the glucose PTS in Bacillus subtilis. Genetic inactivation of M5005_spy1692 significantly reduced transport rates of radiolabelled maltose and maltotriose, but not glucose, leading us to propose its reannotation as malT for maltose transporter. The DmalT, DmalE and DmalE:malT strains were significantly attenuated in their growth in human saliva and in their ability to catabolize a-glucans digested by purified human salivary a-amylase. Compared with wild-type, the three isogenic mutant strains were significantly impaired in their ability to colonize the mouse oropharynx. Finally, we discovered that the transcript levels of maltodextrin utilization genes are regulated by competitive binding of the maltose repressor MalR and catabolite control protein A. These data provide novel insights into regulation of the GAS maltodextrin genes and their role in GAS host-pathogen interaction, thereby increasing the understanding of links between nutrient acquisition and virulence in common human pathogens.

Study of the maltose/maltodextrin binding protein MalE in Escherichia coli has resulted in fundamental insights into the molecular mechanisms of microbial transport. Whether gram-positive bacteria employ a similar pathway for maltodextrin transport is unclear. The maltodextrin binding protein MalE has previously been shown to be key to the ability of group A Streptococcus (GAS) to colonize the oropharynx, the major site of GAS infection in humans. Here we used a multifaceted approach to elucidate the function and binding characteristics of GAS MalE. We found that GAS MalE is a central part of a highly efficient maltodextrin transport system capable of transporting linear maltodextrins that are up to at least seven glucose molecules long. Of the carbohydrates tested, GAS MalE had the highest affinity for maltotriose, a major breakdown product of starch in the human oropharynx. The thermodynamics and fluorescence changes induced by GAS MalE-maltodextrin binding were essentially opposite those reported for E. coli MalE. Moreover, unlike E. coli MalE, GAS MalE exhibited no specific binding of maltose or cyclic maltodextrins. Our data show that GAS developed a transport system optimized for linear maltodextrins longer than two glucose molecules that has several key differences from its well-studied E. coli counterpart.Analysis of microbial carbohydrate physiology has been a fertile area of scientific research for many decades. Fundamental discoveries in the areas of transcriptional regulation, selective nutrient utilization, and molecular transport have been derived from studies of microbial carbohydrate acquisition and processing (13,27,34). For example, the uptake and utilization of maltose/maltodextrins by Escherichia coli has become a model for understanding how microbes transport and use complex sugars (3).The study of E. coli MalE, the periplasmic substrate binding protein of the maltose/maltodextrin ATP binding cassette transporter, has been a particularly fruitful area of investigation (32, 33). Although E. coli MalE binds to a variety of ␣-1,4-linked oligoglucosides, including linear, cyclic, reduced, and oxidized maltodextrins, only a portion of the bound ligands is subsequently transported into the cell (10). The interaction of purified E. coli MalE with the actively transported substrates maltose and maltotriose causes an increase in the E. coli MalE maximum emission wavelength (10, 39). The change in the fluorescence emission spectrum correlates with the closed and open forms of the E. coli . The closed form is needed for active transport to occur (11). The binding of E. coli MalE to substrates that are actively transported results in an endothermic reaction that is entropy driven (40). Conversely, the binding of E. coli MalE to nontransported substrates is exothermic and results in a decrease in the maximum fluorescence emission wavelength of E. coli MalE (9, 40). Therefore, study of E. coli MalE has generated data showing two major modes of ligand binding: one in which an endothermic reaction driven by...

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 ΔamyA strain had a slower rate of translocation across human pharyngeal epithelial cells. Consistent with this finding, the ΔamyA 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 to 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 employs human salivary α-amylase for its own metabolic benefit.