Biology Reference
In-Depth Information
Fig. 2.1 (A) Schematic representation of the protease domains of human cathepsins. All cysteine
cathepsins are expressed as polypeptides consisting of a signal sequence, a propeptide, and a
catalytic domain. The length of the domains is depicted in the graph. The signal peptide is cleaved
off at the site of the translocation into the endoplasmic reticulum. The propeptide is cleaved in the
increasingly acidic environment of the endosomal/lysosomal system resulting in a fully active
catalytic domain of the cathepsins. (Ba) Ribbon structure of cathepsin K revealing the L and R
domain organization of cathepsin molecules. The active site is located between both domains with
the L domain harboring the active site cysteine and the R domain containing the histidine residue.
(Bb) View on the top of the cathepsin K molecule showing the catalytic diad
compartment; and third, the propeptide acts as a high-affinity reversible inhibitor
preventing the premature activation of the catalytic domain.
The catalytic domains of human cathepsins are between 214 and 260 amino
acids in length and contain the highly conserved active sites consisting of a
