A tyrosyl‐tRNA synthetase variant that is responsible for Dominant Intermediate Charcot‐Marie‐Tooth disorder Type C displays decreased fidelity

Abstract

Charcot‐Marie‐Tooth disorder (CMT) is the most common inherited peripheral neuropathy, affecting 1 in 2,500 people in the U.S. Mutations in over 30 different genes have been found to give rise to CMT, including the genes encoding the glycyl‐, alanyl‐, and tyrosyl‐tRNA synthetases. There is currently no cure for CMT.Three mutations in the gene encoding the human cytoplasmic tyrosyl‐tRNA synthetase, G41R, Δ(153–156), and E196K, have been found to give rise to Dominant Intermediate Charcot‐Marie‐Tooth disorder, Type C (DI‐CMTC). Based on modeling studies, we postulated that the E196K substitution affects the fidelity of tyrosyl‐tRNA synthestase. To test this hypothesis, the ability of the E196K variant to catalyze the misacylation of noncognate tRNAs was investigated. We find that the E196K variant is ~100‐fold more efficient at aminoacylating tRNATyr variants containing a noncognate G1:C72 base pair than is the wild type enzyme. Replacing Glu 196 with alanine also decreases the fidelity of the enzyme, indicating that Glu 196 acts as an anti‐determinant to prevent the misacylation of tRNAs containing a G1:C72 base pair. This observation suggests that DI‐CMTC is due to misincorporation of tyrosine into proteins, leading to defects in either their stability or ability to fold correctly. This research is supported by MDA 4268 to EAF.