University of Michigan Chemical Biology Doctoral Program
Our laboratory focuses on three distinct areas of study,
(1) Centromere-specific Nucleosomes
(2) Histone Chaperones
Kinetochore ensures faithful segregation of sister chromatids during mitosis by connecting centromeric DNA and spindle microtubules. Especially, inner kinetochore components recognize centromeric DNA and build up the platform for kinetochore assembly. Two different types of centromeres, point centromere (budding yeast) and regional centromere (fission yeast to human), have been reported. Genetic and molecular mechanisms of inner kinetochore at point centromere are relatively well studied, but the recruiting mechanism of the centromere-specific nucleosomes at regional centromere and its epigenetic features are not well understood. My laboratory focuses on understanding these processes using structural and biochemical approaches. Especially, we focus on the centromere-specific nucleosome recruitment mechanisms in fission yeast and human.
Histone chaperones (HCs), such as Asf1, Rtt106, CAF-1, HIRA, and FACT, play important roles in nucleosome assembly during DNA replication and DNA repair. Newly synthesized H3:H4 dimer is captured by Asf1 and acetylated by histone acetyltransferases (histone H3 Lys56). Following acetylation, H3-H4 dimers are handed off to the next set of chaperones, CAF-1 and Rtt106, which proceed to deposit the histones onto nascent DNA. HIRA is responsible for DNA replication independent histone assembly and FACT is involved in nucleosome disassembly and reassembly. Understanding nucleosome assembly mechanisms by its chaperones is a crucial not only to understand how newly synthesized histones are recruited during DNA replication and repair, but also important to reveal transferring mechanism of epigenetic information to newly incorporated nucleosomes. As a long-term goal, We like to propose the structural and biochemical studies of HCs and address questions of: What are structural features of those HCs as it is and as a complex with its substrates, histones? How HCs recognize and stabilize histones in solution? How HCs distinguish histone variants, e.g. histone H3.1 by CAF-1 and histone H3.3 by HIRA? What is the effect of H3 acetylation in transferring histones from Asf1 to either Rtt105 or CAF-1 and eventually nucleosome incorporation?
Sestrins (Sesn) are stress-inducible, highly conserved proteins in animal kingdom. Human and mouse contain three Sesns (Sesn1, Sesn2, and Sesn3) and single Sesn is available in drosophila and C.elegans. Sesn maintains metabolic homeostasis and protects cells from various stresses, such as DNA damage, oxidative stress, and hypoxia. It has been evidenced that stress-induced p53 and FoxO upregulates Sesn and then activated Sesn influences on AMPK and mTOR pathway to react on cellular stress.
Function as an antioxidant modulator of peroxiredoxins has been proposed based on the sequence homology of N-terminal Sesn with a disulfide reductase, AhpD, but many of essential sestrin functions, such as activating AMPK, do not require this reductase activity. Therefore, it is still obscure what is the exact role of Sestrins despite their functional significance in cellular level.
In collaboration with Dr. Jun-Hee Lee from UM, we try to understand the biochemical function of Sestrin by using structural and biochemical approaches.