The Acinetobacter baumannii Autotransporter Adhesin Ata Recognizes Host Glycans as High-Affinity Receptors

Acinetobacter baumannii is a significant opportunistic pathogen responsible for infections of the lung, blood, skin, urinary tract, and soft tissues, with some strains exhibiting almost complete resistance to commonly used antibiotics. This multidrug resistance, together with a dearth of new antibiotic development, mean novel methods of treatment and prevention are urgently needed. Although many A. baumannii factors required to colonize the host have been identified, little is known about the specific host molecules recognized by these factors. A. baumannii produces a trimeric autotransporter adhesin known as Ata that has been previously demonstrated to bind components of the host cell's extracellular matrix, which are often heavily glycosylated. We hypothesized that Ata would exhibit lectin activity which would play a role in adherence to the host cell surface. Our biophysical analysis using glycan arrays and surface plasmon resonance demonstrated that Ata binds galactose, N-acetylglucosamine, and galactose (β1-3/4) N-acetylglucosamine with high-affinity. These structures are present on many of the proteins which were previously reported to be bound by Ata. We also demonstrated that the recognition of human plasma fibronectin by Ata requires this ability to bind glycans, as the interaction between Ata and fibronectin does not occur when fibronectin is deglycosylated. This strongly suggests a key role for Ata lectin activity during host adherence. This information will assist in directing the development of new and effective treatments to block host interactions using glycans and/or novel compounds in multidrug resistant A. baumannii infections.