Inhibitor_I29 Cathepsin propeptide inhibitor domain (I29)
SMART ACC:	SM000848
Description:	This domain is found at the N-terminus of some C1 peptidases such as Cathepsin L where it acts as a propeptide. There are also a number of proteins that are composed solely of multiple copies of this domain such as the peptidase inhibitor salarin. This family is classified as I29 by MEROPS. Peptide proteinase inhibitors can be found as single domain proteins or as single or multiple domains within proteins; these are referred to as either simple or compound inhibitors, respectively. In many cases they are synthesised as part of a larger precursor protein, either as a prepropeptide or as an N-terminal domain associated with an inactive peptidase or zymogen. This domain prevents access of the substrate to the active site. Removal of the N-terminal inhibitor domain either by interaction with a second peptidase or by autocatalytic cleavage activates the zymogen. Other inhibitors interact direct with proteinases using a simple noncovalent lock and key mechanism; while yet others use a conformational change-based trapping mechanism that depends on their structural and thermodynamic properties.
InterPro ACC:	IPR013201
InterPro abstract:	This entry represents a peptidase inhibitor domain, which belongs to MEROPS peptidase inhibitor family I29. The domain is also found at the N terminus of a variety of peptidase precursors that belong to MEROPS peptidase subfamily C1A; these include cathepsin L, papain, and procaricain ( P10056 ) [ expand This entry represents a peptidase inhibitor domain, which belongs to MEROPS peptidase inhibitor family I29. The domain is also found at the N terminus of a variety of peptidase precursors that belong to MEROPS peptidase subfamily C1A; these include cathepsin L, papain, and procaricain ( P10056 ) [ PUBMED:8939744 ]. It forms an α-helical domain that runs through the substrate-binding site, preventing access. Removal of this region by proteolytic cleavage results in activation of the enzyme. This domain is also found, in one or more copies, in a variety of cysteine peptidase inhibitors such as salarin [ PUBMED:14505823 ]. collapse
Family alignment:	View the Family alignment or the Alignment consensus sequence
There are 12 833 Inhibitor_I29 domains in 12 538 proteins in SMART's NRDB database.

Taxonomic distribution of proteins containing Inhibitor_I29 domains

The tree below includes only several representative species and genera. The complete taxonomic breakdown of all proteins containing Inhibitor_I29 domains can be accessed here. Click the counts or percentage values to display the corresponding proteins.

Predicted cellular role

Cellular role:	Interaction (with the environment)

KEGG pathways involving proteins which contain this domain

This information is based on the mapping of SMART genomic protein database to KEGG orthologous groups. Percentages are related to the number of proteins containing a Inhibitor_I29 domain which could be assigned to a KEGG orthologous group, and not all proteins containing Inhibitor_I29 domains. Please note that proteins can be included in multiple pathways, ie. the numbers below will not add to 100%.

KEGG pathways

Some of these pathways are included in the interactive Pathways Explorer overview maps. Select an overview map and click the button below to highlight them in iPath.

KEGG orthologous groups

Some of these KOs are included in the interactive Pathways Explorer overview maps. Select an overview map and click the button below to highlight them in iPath.

3D structures in PDB containing this domain

Links to other resources describing this domain

InterPro	IPR013201
Pfam	Inhibitor_I29