When I moved from Biochemistry to Dentistry over thirty years ago little did I know that I would be so grateful for my initial training in protein structure and function I received from Professor Syd Leach. Hence it is an honour for me to present the Leach lecture in 2015. My journey started in dental research trying to understand how a small, multiphosphorylated protein in saliva called Statherin could form metastable, supersaturated calcium phosphate solutions. Using newly developed synthetic strategies to synthesize the phosphoseryl/acidic cluster sequence, as well as casein phosphopeptides containing a similar motif and NMR, x-ray diffraction, EM, cross-linking and other techniques we were able to demonstrate that the phosphopeptides encapsulated nanoclusters of amorphous calcium phosphate ions. These phosphopeptide nanocomplexes have been shown to repair early stages of tooth decay in clinical trials and are now available in a range of dental professional and consumer products. The journey then moved on to the study of the aetiology of chronic periodontitis, where we discovered the major bacterial pathogen Porphyromonas gingivalis released protease-covered vesicles into the host to produce localised vascular disruption and immune dysregulation. We determined the crystal structure of the major protease required for virulence designated Kgp and have developed a vaccine targeting the protease which has been shown to be very effective in animal models of disease in studies with our collaborators CSL and Sanofi Pasteur. Investigations into how P. gingivalis secreted Kgp and covalently attached the protease at the cell surface led to the discovery of a novel bacterial secretion system, the Type IX secretion system. We have shown this system is present in many bacterial pathogens and involves a novel gram-negative sortase and LPS-related outer membrane anchor. Targeting this secretion system may be an effective new approach to inhibit a range of bacterial pathogens.