The function of MMP21 (matrix metallopeptidase 21, ENSG00000154485) is as follows. Plays a specialized role in the generation of left-right asymmetry during embryogenesis. May act as a negative regulator of the NOTCH-signaling pathway (PubMed:26429889, PubMed:26437028). Cleaves alpha-1-antitrypsin (PubMed:12617721). {ECO:0000269|PubMed:12617721, ECO:0000269|PubMed:26429889, ECO:0000269|PubMed:26437028}.