Dual function in both nitrogen assimilation and in protection against acid stress during infection (PubMed:24586151). Involved in asparagine uptake (PubMed:24586151). Asparagine transport is partially impaired in the mutant. Knockout mutant is impaired in nitrogen incorporation from asparagine into other amino acids, such as glutamate and glutamine. Growth of the knockout strain is greatly reduced at pH 5.5 in the presence of asparagine as sole nitrogen source. Mutant is not attenuated in immune-competent mice. Belongs to the amino acid-polyamine-organocation (APC) superfamily. Amino acid transporter (AAT) (TC 2.A.3.1) family.