Function of a novel Mycobacterium tuberculosis lipase and its interaction with host proteins

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ABSTRACT Tuberculosis (TB) is a worldwide public health concern because of its high morbidity and mortality. The causative pathogen of TB, Mycobacterium tuberculosis (Mtb), has a unique mycolic acid-rich cell envelope, and can induce accumulation of lipids in the host cells. Inside cells, it exploits host lipids as important nutrients for its infection and long-term intracellular survival. Emerging evidences support that some lipases secreted by Mtb play vital roles in its intracellular persistence. However, the exact functions of these Mtb-secreted lipases and mechanisms that channel their interactions with host cytosolic proteins remain to be unraveled. Previously, we determined that Mtb Rv1075c belongs to a GDSL-like lipase family with a deacylase activity and hydrolyzes triacetin and tributyrin. The gene-disrupting mutation of rv1075c attenuates Mtb’s intracellular growth in macrophages and reduces bacterial load in the infected mice. Recently, we observed that Rv1075c’s lipase activity was enhanced when macrophage lysate was added into the enzymatic reaction, indicating that some eukaryotic factors contribute to boosting Rv1075c’s lipase activity. Subsequently, we performed an ultimate yeast 2-hybrid to screen for host proteins interacting with Rv1075c. We have identified that vimentin (VIM) is one of the proteins interacting with Rv1075c. It has been reported that VIM in adipocytes forms a scaffold around lipid droplets and VIM is a functional partner of lipase to facilitate lipolysis. Combining these evidences with our data, we hypothesize that Mtb Rv1075c interacts with VIM that scaffolds host lipid droplets in macrophages, and the interaction facilitates Rv1075c’s activity in lipolysis so that Mtb can utilize host lipids as energy source for its intracellular persistence. The objective of our proposed studies is to identify mechanism of Rv1075c in the process of accessing host lipid droplets in macrophages and determine its interaction with host VIM protein and the impact of this interaction on Mtb intracellular growth. We will test this hypothesis by pursuing two specific aims: 1) Identify the mechanism by which Mtb Rv1075c interacts with the eukaryotic cytosolic VIM; 2) Determine whether the Rv1075c-VIM interaction enhances Rv1075c’s lipase and phospholipase A activity and facilitates Mtb intracellular survival in macrophages. The proposed research will uncover mechanism of the Rv1075c-VIM interaction and address fundamental questions about how the Rv1075c-VIM interaction affects Mtb intracellular survival and growth. The results from these studies will expand our knowledge of Mtb’s utilization of host lipids during infection and will lead to discovery of new mechanisms of Mtb pathogenesis.