The common neuromuscular disorder Charcot-Marie-Tooth Disease Type IA (CMTD) is caused by genetic defects associated with the gene encoding the tetraspan membrane protein peripheral myelin protein 22 (PMP22). These defects lead to changes in the level of functional PMP22 which is produced during myelination-- changes which sometimes result in severe myelin defects. One class of aberrations are dominant missense mutations which lead to PMP22 having an altered amino acid sequence. These seemingly minor changes in amino acid sequence typically result in misfolding/mistrafficking of the nascent PMP22 upon expression into the endoplasmic reticulum, such that the protein is unable to properly assemble and traffic to the cell membrane. While misfolding of PMP22 has been documented in elegant detail at the cell biological level, very little is known about the fundamental molecular structural and energetic factors which govern the partitioning of nascent PMP22 and other membrane proteins between productive folding/trafficking pathways versus terminally misfolded pathways. This project is designed to address this lack of knowledge by initiating studies of the folding and misfotding of wild type and disease-associated mutant forms of PMP22 using purified proteins, advanced biophysical methods, and well-controlled experimental conditions. The four mutants being chosen for study are those upon which available mouse models for CMTD are based. Wild type and mutant forms of PMP22 will be overexpressed, purified, and subjected to structural studies using various techniques. The stabilities of wild type and disease-associated mutants will be examined to see if protein instability is likely to be a factor related to the increased misfolding of the mutants. Folding kinetic studies will also be undertaken to elucidate rates and structural aspects of folding and misfolding pathways. Finally, the determination of the high resolution structure of wild type PMP22 will be pursued using high resolution NMR and X-ray crystallographic methods. These studies will shed light on the fundamental molecular basis for CMTD Type IA. Moreover, these studies may lead directly to the formulation of therapeutic strategies for CMTD which are based upon modulating the efficiency of productive PMP22 folding/trafficking.
| Myers, Jeffrey K; Mobley, Charles K; Sanders, Charles R (2008) The peripheral neuropathy-linked Trembler and Trembler-J mutant forms of peripheral myelin protein 22 are folding-destabilized. Biochemistry 47:10620-9 |
| Myers, Jeffrey K; Beihoffer, Lauren A; Sanders, Charles R (2005) Phenotology of disease-linked proteins. Hum Mutat 25:90-7 |
