Project Summary/Abstract Infections due to Gram-negative bacteria and mycobacterium tuberculosis (Mtb) pose a serious threat to human health. These organisms produce especially complex cell envelopes consisting of a double layer of membranes that are essential for survival. This cell envelope also functions as a physical barrier to block entry of many classes of antibiotics and thereby render them ineffective. This research is directed towards understanding the structure and function of three protein transporters responsible for cell envelope assembly. Each of these transporters represents one of the three major transporter families, namely ABC transporters, MOPS transporters, and RND transporters. To understand how these transporters move their complex glycolipid cargo, biochemical and structural studies will be undertaken. Intermediates and inhibitors of transport and assembly of will be characterized structurally, biochemically, and in cells. A better understanding of these proteins’ roles in cell envelope assembly will lead to new therapies to treat resistant infections.