Enzyme / serine protease · BEGINNER LESSON
Proteinase K
Proteinase K is a fungal serine protease, meaning it is an enzyme from fungus that cuts peptide bonds in proteins. It is widely used because it stays active under harsh conditions and can digest proteins and nucleases during nucleic acid purification.
What it is and what is measured
Proteinase K is a protease, also called a proteinase or peptidase, because it hydrolyzes peptide bonds in proteins. It is a fungal serine protease from Tritirachium album, and its activity is often measured by how well it digests proteins such as keratin or unwanted enzymes in a sample. Researchers also study its three-dimensional structure and catalytic mechanism to understand how the enzyme works at its active site.
[1] The EMBO Jounal vol.3 no.6 [2] A preliminary neutron crystallographic study of proteinase K at pD 6.5 [3] Research Applications of Proteolytic Enzymes in Molecular Biology
How it works
Proteinase K is an endopeptidase, meaning it cuts peptide bonds within a protein chain rather than only at the ends. It uses a conserved catalytic triad of histidine, aspartic acid, and serine at the active site. In this enzyme family, the exact chemical role of the histidine is a mechanistic question, and neutron crystallography is used to locate hydrogen atoms and help answer it. Proteinase K preferentially cleaves on the carboxylic side of aromatic, aliphatic, or hydrophobic amino acid residues.
[2] A preliminary neutron crystallographic study of proteinase K at pD 6.5 [3] Research Applications of Proteolytic Enzymes in Molecular Biology
Why it is useful
Proteinase K remains active in low concentrations of SDS and can also work in the presence of denaturants such as SDS and urea, and even chelating agents. Because of this, it can digest proteins and inactivate nucleases that would otherwise damage DNA or RNA during nucleic acid purification. This makes it a common tool for isolating nucleic acids in high yield.
[1] The EMBO Jounal vol.3 no.6 [2] A preliminary neutron crystallographic study of proteinase K at pD 6.5 [3] Research Applications of Proteolytic Enzymes in Molecular Biology
What limits or qualifies the picture
The sources also note that Proteinase K depends on a Ca2+ ion for stability, although it retains much of its protease activity after treatment with EDTA, a chelating agent that binds metal ions. Its enzyme family is evolutionarily distinct from the trypsin clan, even though both use similar catalytic triads. Structural studies have been done by X-ray diffraction and preliminary neutron crystallography, but the neutron study was aimed at deeper understanding rather than a finished full mechanism.
[1] The EMBO Jounal vol.3 no.6 [2] A preliminary neutron crystallographic study of proteinase K at pD 6.5
SEE THE IDEA
Proteinase K in nucleic acid preparation
Proteinase K comes from Tritirachium album and is a serine protease.
It hydrolyzes peptide bonds, especially near hydrophobic, aromatic, or aliphatic residues.
It stays active with SDS, urea, and some chelating agents.
It digests proteins and nucleases that could lower yield or damage nucleic acids.
Source enzyme -> protein cutting -> survives harsh reagents -> cleaner nucleic acid isolation
Proteinase K is used because its protease activity can continue while other sample proteins and nucleases are being removed.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.