Structural Investigations of Nuclear Receptor and Inositol Kinase Family Members

Abstract

Mammalian cells respond to environmental stimuli by transforming the presence of a novel chemical into actionable biological processes via receptors located both internally and at the cell surface. Nuclear receptors are one class of receptors that exert their actions by binding directly to DNA, and in concert with transcriptional co-regulators, alter genetic programs. Liver Receptor Homolog-1 (LRH-1; NR5A2) is a monomeric nuclear receptor that regulates a diverse array of biological processes. Although detailed structural information was available for individual domains of LRH-1 at the start of this study, it was unknown how these domains exist in the intact nuclear receptor. Here, an integrated structural model of human full-length LRH-1 was developed using a combination of HDX-MS, XL-MS, computational docking and SAXS. The model predicts several inter-domain interactions, which were confirmed via structural and functional analyses. Together, these data support individual LRH-1 domains interacting to influence receptor structure and function. Recent studies have also shown inositol phosphates participate in certain transcriptional co-regulator complexes. Inositol polyphosphate multikinase (IPMK) is a member of the inositol kinase family, catalyzing phosphorylation of several inositol phosphates and the signaling phospholipid PI(4,5)P2. Here, kinetic and crystallographic analyses of an engineered human IPMK lacking all disordered domains shows the native IPMK disordered domains decrease IPMK enzymatic activity in vitro and the enzyme exhibits a conserved ATP grasp fold. Together, these studies provide molecular models of an intact monomeric nuclear receptor and an engineered inositol kinase, adding mechanistic insight into proteins contributing to transcriptional control.