These specific
proteases use
hydrolysis to break down gelatin through two sequential steps. The first produces polypeptide products, followed by amino acids (typically
alpha amino acids). The
substrate in this case is gelatin, and the products are the polypeptides formed. Gelatinase binds to the substrate, gelatin, due to specificity of binding interactions on cell surface. The catalysis, associated with a zinc ion and amino acid residues, breaks the peptide bonds into polypeptides through cleavage. Polypeptides are further converted into amino acids, the second sequential step and product of the reaction. Additional proteins, such as
TIMP-2 and other
TIMPs, work as inhibitors to regulate and control the enzymatic pathway by binding to the gelatinase active site, which prevents the breakdown of substrate.
Cell surface association Gelatinases can regulate enzymatic activation and activity by interactions on the cell surface. Surface proteins regulate functions such as localization,
inhibition, and internalization. Enzyme binding to the surface brings it in close accord with certain substrates in the pericellular space in order to regulate function of the MMPs. Localization allows them to degrade specific elements of the EMC by close cell surface association.
Crystal structures Gelatinases contain a
catalytic domain (located in the C-terminal region), which is essential for enzymatic activity and hydrolysis of peptide bonds in substrate molecules. This domain contains five beta strands in a twisted
beta sheet bound together by three
alpha helicies. The active site is located in between a beta strand and an alpha helix, holding
histidine residues, with another helix holding a histidine residue, creating loops. These histidines are in relation to a catalytic zinc ion, playing an important role in catalyzing the hydrolysis of peptide bonds in proteins.Also in the C terminal region, there is a hemopexin-like domain, which interacts with a part of the cell membrane. Contributing to enzyme specificity, affinity, and localization, made of four blades with antiparallel beta stranded beta sheets. Furthermore, there is the
fibronectin type II (FNII), important for recognition, folding, and mediation of gelatin interactions due to the involvement of protein-protein interactions, and are crucial for substrate specificity. FNII consists of two double-stranded antiparallel beta sheets. The primary structures of individual MMPs may have different domain compositions, and the arrangement of the domains and structures help with folding and stability of the enzyme, as folding is what promotes enzyme activity.
Active sites Some of the gelatinases are proteinases that are zinc-dependent. The known
active sites of these proteins are located in the catalytic domains, and typically contain a zinc atom at known site, which is important for catalysis. The active sites also contain
histidine and
glutamate residues, establishing the catalytic zinc-binding active site region. These residues are in
coordination with the zinc ion for stabilization and conformation. This active site aids the hydrolysis of peptide bonds in substrates, such as gelatin and collagen, due to coordination of zinc ions and amino acid
residues. They also influence gelatinase catalysis and binding of substrates. ==References==