Required to protect lysosomal transporter MFSD1 from lysosomal proteolysis and for MFSD1 lysosomal localization. Interacts (via lumenal domain) with lysosomal protein MFSD1; the interaction starts while both proteins are still in the endoplasmic reticulum and is required for stability and lysosomal localization of MFSD1. Transcription is activated by TFEB. Highly N-glycosylated. N-glycosylation is essential for GLMP stability and for MFSD1 lysosomal localization. Belongs to the GLMP family. According to PubMed:18021396, it binds DNA and acts as a transcription factor. However, the localization in lysosomes which was confirmed by different groups and the presence of transmembrane region strongly suggests that it does not have coactivator activity.