Our laboratory investigates the molecular bases of functions of a number of integral membrane protein families. We combine x-ray crystallography together with functional analyses with a range of biochemical and biophysical techniques to approach these problems. 1) Structural Basis for Substrate Recognition by the Ankyrin Repeat Domain of Human DHHC17 Palmitoyltransferase - DHHC enzymes catalyze palmitoylation, a major post translational modification that regulates a number of key cellular processes. There are up to 24 DHHCs in mammals and hundreds of substrate proteins that get palmitoylated. However, how DHHC enzymes engage with their substrates is still poorly understood. There is currently no structural information about the interaction between any DHHC enzyme and protein substrates. DHHC17 is one of the most important palmitoyltransferases in the normal functioning of the brain. We have investigated the structural and thermodynamic bases of interaction between the ankyrin repeat domain of human DHHC17 (ANK17) and Snap25b, one of its canonical substrates. We solved a high-resolution crystal structure of the complex between ANK17 and a peptide fragment of Snap25b. Through structure-guided mutagenesis, we discovered key residues in DHHC17 that are critically important for interaction with Snap25b. We further extended our finding by showing that the same residues are also crucial for the interaction of DHHC17 with Huntingtin, one of its most physiologically relevant substrates. 2) In Vitro reconstitution and biochemical studies of iron transport into mitochondria - In this project, we are focusing our attention on mitochondrial inner membrane transporters that bring iron into mitochondria. Subsequently, the iron is utilized in the biosynthesis of heme, a central component of the heme in hemoglobin, myoglobin, and cytochromes , and iron-sulfur clusters, important cofactors required for proteins involved in a wide range of cellular activities, viz. electron transport in respiratory chain complexes, regulatory sensing, photosynthesis and DNA repair. In spite of its pivotal importance in biology, there are no reliable in vitro reconstituted transport assays for iron transporters. We have set up a robust in vitro transport assay for Mitoferrin, the only known major transporter of iron into mitochondria. We are currently investigating the metal ion promiscuity of Mitoferrin and the importance of highly conserved residues in its function.

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U.S. National Inst/Child Hlth/Human Dev
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Christenson, Eric T; Gallegos, Austin S; Banerjee, Anirban (2018) In vitro reconstitution, functional dissection, and mutational analysis of metal ion transport by mitoferrin-1. J Biol Chem 293:3819-3828
Rana, Mitra S; Kumar, Pramod; Lee, Chul-Jin et al. (2018) Fatty acyl recognition and transfer by an integral membrane S-acyltransferase. Science 359: