Structural Characteristics and Cellular Functions of the MLC1

초록

MLC1 is a plasma membrane protein mainly expressed in astrocytes. Genetic mutations in this protein can lead to megalencephalic leukoencephalopathy with subcortical cysts (MLC). However, the exact function and structure of the MLC1 protein, as well as the pathological mechanism, remain poorly understood. Our previous studies revealed that heterologously expressed wild-type MLC1 primarily localizes at the plasma membrane and induces significant changes in cellular morphology and motility. In contrast, pathogenic mutations such as S280L and P92S do not produce these effects. Additionally, we have determined the transmembrane topology and oligomeric assembly of MLC1 using systematic immunofluorescence staining, chemical crosslinking, negative-staining electron microscopy, and single-molecule photobleaching techniques. To gain further insight into the structure and function of MLC1, we have attempted to characterize the structure and cellular function of MLC1. Preliminary cryo-EM data suggested that the MLC1 protein indeed forms a trimeric assembly. However, the current resolution is not sufficient to assign the side chains due to the orientation bias of MLC1 proteins on the EM grid. We are continuing efforts for creating various orientations of the MLC1 protein to resolve the cryo-EM structure. Interestingly, we found that wild-type and pathogenic mutants have mutually exclusive phosphorylation patterns. A wild-type mimicking mutation in the S280L mutant restored plasma membrane targeting and induced morphological change. Currently, we are screening candidate kinases responsible for these distinct phosphorylation patterns.