Intrinsic disorder in CENP-ACse4 tail and its chaperone facilitates synergistic association for kinetochore stabilization

The kinetochore is a complex multiprotein network that assembles at a specialized DNA locus called the centromere to ensure faithful chromosome segregation. The centromere is epigenetically marked by a histone H3 variant - the CenH3. The budding yeast CenH3, called Cse4, consists of an unusually long and disordered N-terminal tail that has a role in kinetochore assembly. Its disordered chaperone, Scm3 is involved in its centromeric deposition as well as in the maintenance of a segregation-competent kinetochore. The dynamics of the Cse4 N-tail and chaperone interaction have not been studied, leaving a gap in our understanding of their roles at the centromere. Previously, we had shown that Scm3 is an intrinsically disordered protein. Here, using NMR and a variety of biophysical and bioinformatics tools, we show that Cse4 N-tail is also disordered, the two proteins interact with each other at multiple sites, and this interaction reduces the disorder in Scm3; the chain opens up relative to the native state ensemble and the conformational exchange is reduced. Interestingly, this interaction between the two intrinsically disordered protein is fairly specific as seen by positive and negative controls, and is majorly driven by electrostatics as both the proteins have multiple acidic and basic regions. The complex retains a fair amount of disorder, which facilitates a synergistic association with the essential inner kinetochore Ctf19-Mcm21-Okp1-Ame1 complex; a model has been suggested to this effect. Given the abundance of intrinsic disorder in the kinetochore proteins, this type of interaction and adaptation may be prevalent in other proteins as well for mediating kinetochore assembly. Thus, the present study, on one hand, provides significant structural and mechanistic insights into the complex and dynamic process of kinetochore assembly, and on the other hand, illustrates a mechanism that intrinsically disordered proteins would adapt to mediate the formation of complex multiprotein networks, in general. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=67 SRC="FIGDIR/small/504061v1_ufig1.gif" ALT="Figure 1"> View larger version (14K): org.highwire.dtl.DTLVardef@8fe5cforg.highwire.dtl.DTLVardef@138afb1org.highwire.dtl.DTLVardef@96943forg.highwire.dtl.DTLVardef@1deb673_HPS_FORMAT_FIGEXP M_FIG C_FIG