Streptococcus pneumoniae Lipoproteins and ABC Transporters

ATP-binding cassette (ABC) transporters are a major category of membrane-associated bacterial protein structures involved in the transport of a wide range of substrates. Streptococcus pneumoniae has over 60 ABC transporters, most of which are conserved in all strains. Around two-thirds of S. pneumoniae ABC transporters are importers associated with lipoproteins required for the uptake of various substrates including micronutrients, peptides, and sugars. The remaining ABC transporters export quorum-sensing peptides, drugs (including antibiotics), and antimicrobial peptides from the bacterial cytosol. ABC transporter functions are often partially redundant as other ABC and non-ABC transporter systems import the same substrates. Many ABC transporters have important effects on pathogen–host interactions, either by improving bacterial growth in nutrient-restricted conditions, wider effects on bacterial physiology, or by reducing sensitivity to host antimicrobial peptides or to antibiotics. As a consequence, ABC transporters have a fundamental role in S. pneumoniae biology and virulence.