[BK21 Plus Seminar] ▶Subject: Biochemical-genetic investigation of the influence of the polyglutamine tract on huntingtin structure and function ▶Speaker: Ihn Sik Seong, PH.D. (Neurology Department, Harvard Medical School) ▶Date: 4:00 PM/Feb. 17(Wed.)/2016 ▶Place: Life Science Bldg. #104 *Abctract The CAG trinucleotide repeat expansion mutation that is the genetic cause of Huntington’s Disease (HD) elongates a normally variable segment of polyglutamine located sixteen amino acids from the start methionine of the 350kD huntingtin protein to more than about forty residues. To understand this mutation at the level of the fulllength huntingtin HEAT/HEAT-like domain molecule itself, we are using a classical biochemical-genetic strategy that couples the physical analyses of a series of highly purified full-length huntingtins with different polyglutamine tracts to the functional activity of these proteins in a validated cell-free assay (Seong et al. HMG (2010) 19:573-583): enhancement of polycomb repressive complex 2-dependent nucleosome deposition of the histone H3K27me3 mark (PRC2-assay). Our results reveal that full-length huntingtin, which is bisected by a protease sensitive hinge site at residues 1184-1254 into two large arms, assumes a spherical α-helical solenoid shape with a large internal cavity, that involves short-, medium- and long-range intramolecular contacts, with the latter mediating the interaction of the Amino terminal arm with the Carboxyl terminal arm. This 3D shape is globally similar regardless of polyglutamine size. However, polyglutamine length does alter the pattern of full-length huntingtin intramolecular contacts and the pattern of posttranslational modifications, including ‘crosstalk’ between distant phosphosites, such that huntingtin’s polyglutamine tract size and phosphorylation status is associated with the protein’s function activity. The 3D closed α-helical shape assumed by full-length huntingtin’s HEAT/HEAT-like rich domains, therefore, provides an elegant solution to the conundrum of full-length huntingtin as the polyglutamine tract size dependent disease-initiator. Our results pave the way for highresolution studies that will be required to determine in detail the influence of its polyglutamine segment on the structure of full-length huntingtin, while our biochemicalgenetic approach provides a route to identify factors that can selectively manipulate fulllength mutant huntingtin without affecting normal full-length huntingtin activity ▶Inquiry: Prof. Sang Ki Park (279-2349) * This seminar will be given in English. please refrain from taking photos during seminars. *