Scytalidocarboxyl peptidase B, also known as Scytalidoglutamic peptidase and Scytalidopepsin B (, obsolete names include ''Scytalidium aspartic proteinase B'', ''Ganoderma lucidum carboxyl proteinase'', ''Ganoderma lucidum aspartic proteinase'', ''Scytalidium lignicolum aspartic proteinase B'', ''SLB'') is a

proteolytic enzyme A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the for ...

. It was previously thought to be an

aspartic protease Aspartic proteases are a catalytic type of protease enzymes that use an activated water molecule bound to one or more aspartate residues for catalysis of their peptide substrates. In general, they have two highly conserved aspartates in the activ ...

, but determination of its molecular structure showed it to belong a novel group of proteases,

glutamic protease Glutamic proteases are a group of proteolytic enzymes containing a glutamic acid residue within the active site. This type of protease was first described in 2004 and became the sixth catalytic type of protease. Members of this group of protease h ...

. The protease has a unique structure and a novel catalytic dyad (E136 and Q53) in its active site. The active-site residues, glutamic acid (E) and glutamine (Q), was used to coin the name of the family of

protease A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalyzes (increases reaction rate or "speeds up") proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the ...

s, eqolisins, to which Scytalidoglutamic peptidase B belongs. This enzyme catalyses the following

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

Hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile. Biological hydrolys ...

of proteins with broad specificity, cleaving Phe²⁴-Phe and Tyr²⁶–Thr but not Leu¹⁵-Tyr and Phe²⁵-Tyr in the B chain of insulin. It also cleaves the His⁶–Pro bond of

angiotensin I Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the a ...

, the ability to cleave a peptide bond with Pro in the P1′ position is unusual. This

endopeptidase Endopeptidase or endoproteinase are proteolytic peptidases that break peptide bonds of nonterminal amino acids (i.e. within the molecule), in contrast to exopeptidases, which break peptide bonds from end-pieces of terminal amino acids. For this ...

is isolated from '' Scytalidium lignicolum''. It is an acid protease, and is most active at pH 2.0 when casein is used as substrate. Eqolosins prefer bulky amino acid residues at the P1 site and small amino acid residues at the P1′ site. The substrate specificity of scytalidoglutamic peptidase is unique, particularly in the substrate preferences at the P3 (basic amino acid), P1′ (small amino acid) and P3′ (basic) positions.

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