Apolipoproteins are the protein components of lipoproteins, and their role in lipid transport processes has been well documented. It is much less known that apolipoproteins also play an important role in innate immunity and our research program aims to understand this novel function. To study these critical players in lipid transport processes and innate immunity, we use an invertebrate apolipoprotein as a model system. This protein, apolipophorin III, has a known three-dimensional structure, which is critical to our structure-guided approach. Very few high resolution structures of human apolipoproteins are available, making our model system well suited for our research goals. Through a structure-guided site-directed mutagenesis approach we aim to obtain fundamental knowledge of how apolipoproteins function at the molecular level, gaining critical knowledge of their structure-function relationship. This allows us to understand the molecular basis of diseases associated with apolipoprotein function.