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MalE of Group A Streptococcus Participates in the Rapid Transport of Maltotriose and Longer Maltodextrins ^,

Section of Infectious Diseases, Department of Medicine, Baylor College of Medicine, Houston, Texas, 77030,¹ Department of Chemistry, University of Houston, Houston, Texas, 77024,² Center for Molecular and Translational Human Infectious Diseases Research, The Methodist Hospital Research Institute, Houston, Texas, 77030,³ Department of Pathology,⁴ Structural and Computational Biology and Molecular Biophysics Program, Baylor College of Medicine, Houston, Texas 77030⁵

Received 3 October 2006/ Accepted 11 January 2007

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.

Published ahead of print on 26 January 2007.

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