Structure-based immunogen design in HIV/AIDS vaccine discovery
HIV/AIDS is a global pandemic, and the development of a safe and effective HIV vaccine is one of the most pressing challenges for biomolecular medicine. In a reverse engineering strategy of vaccine discovery, broadly reactive human monoclonal antibodies (mAbs) are identified and their structures, in complex with their cognate epitopes, are determined in order to provide information for engrafting the epitopes onto scaffolds and using them as immunogens which may be able to elicit antibodies with a breadth of neutralizing activity similar to that displayed by the broadly reactive mAbs. Thus, 3D visualization of the cognate HIV epitopes of broadly neutralizing anti-HIV mAbs targeted at immunogenic epitopes is crucial for designing immunogens that induce cross-reactive polyclonal antibody responses in mammals. We have worked synergistically with a team of immunologists, vaccinologists and computational biologists, and we have determined crystal structures of a large panel of anti-HIV 1 mAbs. Our structures of anti-V3 mAbs not only revealed the structural basis explaining why some anti-V3 mAbs are broadly reactive, but also have allowed us to identify conserved structural elements the V3 crown. These conserved structural elements have laid the foundation for designing V3 immunogens for HIV candidate vaccines.
Host-pathogen interactions in urinary tract infection (UTI)
The apical surface of mammalian urothelium is covered by rigid plaques (also know as asymmetric unit membrane or AUM) that are hexagonally packed crystalline arrays of 16-nm particles consisting of four uroplakins (UPs). These uroplakin plaques contribute to the urothelial permeability barrier function, and one of the uroplakins, UPIa, can serve as the receptor for the type 1-fimbriated uropathogenic E. coli (UPEC). UPEC gains a foothold in the urinary tract by binding, via its adhesin FimH, to the urothelial receptor. We have obtained a 6Å resolution cryo-EM structure of the 16-nm uroplakin particle and showed that FimH binding can induce large conformational changes of the extracellular domains as well as the transmembrane helices of the uroplakins. These results suggest that bacterial attachment can induce a novel mechanism of transmembrane signal transduction leading to bacterial invasion and establishment of urinary tract infection (UTI), one of the most common infectious diseases. We are continuing our efforts in studying the structure-function relationship of the 16-nm particle and the mechanism of bacterial binding-induced signal transduction by electron microscopy and electron tomography. Our results should lead to a better understanding of the structural bases of urothelial plaque function, and of the possible roles of urothelial plaques in urinary tract infection.