Asparagine couples group A Streptococcal metabolism to virulence

Abstract

Streptococcus (GAS) is a highly adapted and human-restricted pathogen causing a wide variety of infections, some life-threatening1. This ability is linked to the expression of many virulence factors, whose transcription is regulated by the two-component system, CovR/S2-5. Here, we show that genome transcription of GAS cultured in a chemically defined medium (CDM) is globally affected when supplemented with asparagine (Asn), including increased expression of many virulence genes. For the first time, we report that GAS solely depends on asparagine synthetase (AsnA) for Asn synthesis, on the ABC transporter (GlnPQ) to import Asn, and on the asparaginase (AsnB) to maintain a precisely balanced intracellular Asn concentration. Furthermore, we show that mutants defective in either asnA, glnP, or asnB express significantly lower levels of virulence factors in CDM and are severely attenuated in the sublethal murine model of human GAS soft-tissue infection. We further show that the synthesis and import of Asn in GAS are ATP-dependent and negatively regulated by intracellular Asn. Thus, Asn availability controls the intracellular ATP level. When ATP becomes limiting, CovR phosphorylation decreases. This augments GAS growth rate, virulence production, metabolism, and vice versa when the ATP level increases. Furthermore, excess Asn accumulates inside GAS in AsnB mutant, destroying the balance between Asn and ATP. We discuss the high similarity between these mechanistic principles of the Asn-mediated control of GAS virulence and metabolism to the Asn-mediated control of tumor growth6, indicating evolutionary significance.