The function of MKLN1 (muskelin 1, Ensembl gene identifier ENSG00000128585) is as follows. Component of the CTLH E3 ubiquitin-protein ligase complex that selectively accepts ubiquitin from UBE2H and mediates ubiquitination and subsequent proteasomal degradation of the transcription factor HBP1 (PubMed:29911972). Required for internalization of the GABA receptor GABRA1 from the cell membrane via endosomes and subsequent GABRA1 degradation (By similarity). Acts as a mediator of cell spreading and cytoskeletal responses to the extracellular matrix component THBS1 (PubMed:18710924). {ECO:0000250|UniProtKB:O89050, ECO:0000269|PubMed:18710924, ECO:0000269|PubMed:29911972}.