Impact of Neurodevelopmental Disorder-Associated Clinical Variants on the Catalytic Activity of KMT5B

Abstract

KMT5B is a lysine methyltransferase that is known for its role in catalyzing H4K20 dimethylation. This post-translational modification is involved in DNA repair and heterochromatin formation. Missense variants found in KMT5B cause a related neurodevelopmental disorder in which patients experience neurodevelopmental phenotypes like developmental delay (DD), intellectual deficits (ID), autism spectrum disorder (ASD), seizures, and motor deficits. However, the impact of these variants on enzyme activity is unknown. In this work, we provide qualitative and quantitative evidence showing the differential impacts of four select clinical missense variants of KMT5B on its lysine methylation activity. Recombinant KMT5B was purified and used for in vitro KMT assays to assess enzyme activity on nucleosome and peptide substrates. While three of the four variants tested showed significant decreases in catalytic activity, one variant had a non-significant decrease. This differential KMT5B catalytic activity raises questions about the relationship between levels of catalytic activity and neurodevelopmental phenotypes. The methods established in this work lay the groundwork for testing additional clinically associated KMT5B variants. Understanding the impacts of these variants on catalytic activity is an important first step in determining their underlying mechanisms that contribute to neurodevelopmental dysfunction.