Towards the NMR solution Structure and the Dynamics of the C-terminal Region of APOL1 and its G1, G2 Variants with a Membrane Mimetic

Abstract

Secreted apolipoprotein L1 (APOL1) is well known as an innate immune factor, protecting against African trypanosomiasis. The intracellular form has multiple functions, including regulating autophagy, intracellular vesicle trafficking, and ion channel activity. The APOL1 protein (G0) has two common variants (denoted G1 and G2) in the C-terminal region and are associated with a high risk of chronic kidney disease (CKD) and progression to end-stage kidney disease. Our previous studies using molecular modeling suggested that APOL1 G1 and G2 stabilize an autoinhibited state of the C-terminus, leading to impaired intracellular interactions with SNARE proteins. To characterize the structural consequence of kidney disease-associated APOL1 variants further, we assigned the C-terminal region proteins using 1H, 13C, 15N multidimensional nuclear magnetic resonance (NMR) spectra in solution in the presence of membrane mimetic dodecylphosphocholine micelles. We then derived models for the three-dimensional structure of APOL1-G0, and -G1 and -G2 variant C-terminal regions using the chemical shifts of the main chain nuclei followed by NMR relaxation measurements. The data suggest that changes in the three-dimensional structure of APOL1 C-terminal region induced by kidney disease-associated variants, not least the alteration of key sidechains and their interactions, could disrupt membrane association and the yet to be characterized protein-protein interactions including its binding partners, such as SNARE proteins. Such interactions could underlie the intracellular mechanisms that mediate the pathogenesis of CKD. In the future, one may try to reverse such structural and dynamics changes in the protein by designing agents that may bind and then mitigate APOL1 variant-associated CKD.