Neuron. 2009 Dec 24;64(6):828-40. Serines 13 and 16 are critical determinants of full-length human mutant huntingtin induced disease pathogenesis in HD mice. Gu X, et al., Yang XW.  UCLA HD: It’s not Just about the polyglutamine By Ray Truant, April 2010 This manuscript describes a genetic experiment in which the investigators sought to find out the potential role of phosphorylation of serines 13 and 16 in huntingtin. These two amino acids are in the middle of the N17 ER-targeting domain defined by out lab in 2007. Previous work from our group showed that mutations that affected the structure of 1-17, somehow affect the ability of mutant huntingtin fragments to be toxic, or to form any aggregates. Past work from Susan Lindquist’s lab showed effect on toxicity by tagging the huntingtin protein, and effects of mutation in another region beside the polyglutamine tract, the polyproline region. The conclusions were simple: structure of regions that flank the polyglutamine tract have the ability to affect the structure of the Polyglutamine tract, and hence toxicity. In a nutshell, Yang’s group find that mutations that mimic phosphorylation of huntingtin, seem to prevent any mutant huntingtin toxicity after one year of life in this mouse model. Ron Wetzel’s lab contributed to show that in vitro, with small synthetic fragments of huntingtin, that these mutations  change the structure of huntingtin aggregates. This leads to a concept of good and bad aggregates in HD, reinforced elegantly by Paul Muchowski’s recent work. So what’s the big deal? This genetic model implies that if we can pharmacologically keep huntingtin phosphorylated at serines 13 and 16, we can reduce, or even prevent the toxicity of mutant huntingtin protein.  Pharmaceutical companies like Novartis  have had great success with compounds that can affect the phosphorylation of proteins being developed into drugs. This mouse experiment also back up work in other model systems that show that there are other regions in the huntingtin protein that can be targeted for drug discovery, besides the polyglutamine expansion, where most of the effort has been focused for the last decade. Where to go from here? The next obvious step is to understand how huntingtin gets phosphorylated and by which kinase enzyme, and which phosphatase enzyme removes the phosphate group. Either promoting the kinase activity or inhibiting the phosphatase activity should have the effect of boosting huntingtin phosphorylation in N17.