A novel attachment mechanism for Burkholderia cepacia complex

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PROJECT SUMMARY Bacterial attachment to host cells is a critical step for pathogenesis. Thus, the prevention of bacterial attachment to host cells is an ideal target to halt disease progression. A severe lack of knowledge of the attachment mechanism of Burkholderia species greatly inhibits our ability to develop effective treatment strategies. Burkholderia cepacia complex (Bcc), consisting of more than 20 species of Gram-negative bacteria, poses a major threat to public health. Bcc causes severe opportunistic lung infections in cystic fibrosis (CF) patients worldwide. CF is a life-threatening condition with no cure and treatment of CF-related infections is difficult. There are about 30,000 people with CF in the United States and more than 70,000 people worldwide. Bcc is also a group of significant pathogens leading to nosocomial infections in other immunosuppressed individuals highlighted by several outbreaks of infection. Our significant research discovery of a novel surface attachment protein from Burkholderia pseudomallei (Sap1Bp), a previously uncharacterized hypothetical protein, has provided an opportunity to investigate a new and, seemingly, universal attachment mechanism exploited by many Burkholderia species. Sap1Bp is functionally conserved across many Burkholderia species, including Sap1 from clinically relevant members of Bcc (Sap1Bcc). There are many attachment mechanisms employed by Bcc and they are complex. However, no associated receptor partners from host cells have been discovered to date, leaving significant knowledge gaps in the understanding of attachment mechanisms in the Bcc. We found that Sap1Bcc contributes significantly to Bcc attachment to the host cells and is required for complete Bcc pathogenesis in multiple animal models. Moreover, we discovered the Sap1 host-cell receptor to be the glycoprotein non-metastatic melanoma protein B (GPNMB), which is associated with various cancers and Alzheimer's disease, revealing a novel and unique interaction that has never been exploited by any bacterial pathogens to attach and invade host cells. In this application, we proposed to explore the mechanisms of this important surface attachment protein Sap1Bcc to interact with its host-cell receptor GPNMB in vitro and the importance of this interaction for in vivo pathogenesis. Aim 1A will characterize Sap1Bcc and GPNMB interaction at the molecular level by determining their interaction affinity and defining the key residues for attachment function, which is critical for future study of its virulence mechanism. Aim 1B seeks to functionally characterize the roles of GPNMB in Sap1Bcc-dependent Bcc attachment to GPNMB knockout and overexpression cells. Aim 1C will investigate the role of GPNMB during Bcc murine infection to determine if the interaction between the novel virulence factor Sap1Bcc and its host cell receptor GPNMB directly contributes to disease. Detailed characterizations of this newly discovered Sap1Bcc /GPNMB interaction could provide potential drug-target and alternative therapeutic strategies toward better treatment outcomes of Bcc infection.