Mutations and substrates of the E3 ubiquitin ligase adaptor Kelch-like 15 and link to neurodevelopmental disorders

Proper early brain development requires appropriate growth of neurons, the primary cell type of the human brain. Neuronal growth is tightly controlled by key molecular machineries, including protein quality control. The balance of protein levels in neurons, which is regulated by the counteracting process of protein synthesis and protein degradation, plays critical role in maintaining normal neuronal function and ensuring optimal neuronal growth. Ubiquitin-proteasome system (UPS) is an essential component of protein degradation machinery. Among all UPS factors, E3 ubiquitin ligases have received particular attention as they determine the fate of targeted proteins. In this dissertation, we particularly focus on Kelch-like 15 (KLHL15), a key component of the E3 ligases, and investigate its link to neurodevelopmental disorders (NDDs).

Here, we report families and individuals within that carry KLHL15 genetic mutations and manifest intellectual disability (ID) and other neurodevelopmental complications. We identified mutations that can increase or decrease KLHL15 activity and elucidated the aberrations of KLHL15 at the molecular level and its functional abnormalities. Understanding the molecular underpinning of ID caused by KLHL15 mutations may help correct such deficit in the future.

Using bioinformatic and biochemical tools, we also searched for potential substrate proteins in neurons that are targeted by KLHL15 for degradation. We identified three members (doublecortin, doublecortin-like kinase 1 and 2) of a unique family of microtubule-associated proteins (MAPs), a group of proteins that regulate cytoskeleton dynamics and promote neuronal growth, as KLHL15 substrates, and provide other candidate proteins whose aberrant regulation by KLHL15 might cause NDDs.