Human Defensins Interact with Porphyromonas gingivalis fimbriae (rFimA)

Human neutrophil peptide a-defensins (HNP) and human b-defensins (HBD) have broad antimicrobial activity against gram-negative and gram-positive bacteria, fungi, and enveloped viruses. These defensins are expressed in neutrophils, epithelia of many organs, and non-epithelial tissues and are present in mucosal secretions. Little is known about their ability to interact and bind to bacterial extracellular appendages. Objective: It was our goal to determine specific interactions among HNP and HBD and the recombinant FimA (rFimA) of P. gingivalis with surface plasmon resonance in the Biacore 3000. Methods: HNP, HBD, and rFimA were suspended in HBS-EP buffer and their purity and concentrations were confirmed by MALDI-TOF and amino acid analysis. rFimA was then immobilized on a CM-5 chip via amine coupling. HNP and HBD, diluted into 100 µg/ml, 50 µg/ml, 10 µg/ml, and 1 µg/ml solutions, were passed over the immobilized rFimA in the flow cell. Binding was determined by an increase in the Resonance Units (RU). All assays were run in triplicate and evaluated using a Spearman rank correlation. Results: Binding of defensins to rFimA was concentration dependent and there was a strong interaction (p < 0.0001) between defensin and concentration. RUs increased significantly for HNP-2 (r = 0.97, p < 0.001), HNP-1 (r = 0.97, p < 0.0001), HBD3 (r = 0.97, p < 0.0001), and HBD2 (r = 0.62, p = 0.328), but not HBD1. Conclusions: Defensins bound to rFimA via surface plasmon resonance and the strength of binding occurred in the following orders: HNP-2 > HNP-1 > HBD3 > HBD2 > HBD1. Subsequent work will focus on the interaction of defensins with rFimA and the role this interaction may have in innate and adaptive immune response to infections caused by P. gingivalis. Supported by NIH/NIDCR T32 DE014678 and R01 DE014390.