You will be shown biomedical passages and your task is to the answer the provided question. Provide a concise and accurate response and do not include any additional text in the response other than the answer.

Question: What is needed for MMP proteins to be functional?

Context: matrix metalloproteinase (MMP)-9
matrix metalloproteinase-3 (MMP-3) gene
matrix metalloproteinases (MMPs)
Matrix metalloproteinase-9 (MMP-9) is a secreted glycoprotein with a major role in shaping the extracellular matrix and a detailed understanding of the secretory mechanism could help identify methods to correct diseases resulting from dysregulation of secretion.
Gelatinase B/matrix metalloproteinase-9 (MMP-9) (EC 3.4.24.35) cleaves many substrates and is produced by most cell types as a zymogen
Extracellular matrix metalloproteinases (MMPs) are a family of zinc-dependent neutral endopeptidases involved in physiological and pathological processes, through the cleavage of extracellular matrix.
Extracellular matrix metalloproteinases (MMPs) are a family of endopeptydases which recquire a zinc ion at their active site, for proteolityc activity.
zinc