3ofi | pdb_00003ofi
Crystal structure of human insulin-degrading enzyme in complex with ubiquitin
Structural highlights
Function[IDE_HUMAN] Plays a role in the cellular breakdown of insulin, IAPP, glucagon, bradykinin, kallidin and other peptides, and thereby plays a role in intercellular peptide signaling. Degrades amyloid formed by APP and IAPP. May play a role in the degradation and clearance of naturally secreted amyloid beta-protein by neurons and microglia.[1] [2] [3] [UBC_HUMAN] Ubiquitin exists either covalently attached to another protein, or free (unanchored). When covalently bound, it is conjugated to target proteins via an isopeptide bond either as a monomer (monoubiquitin), a polymer linked via different Lys residues of the ubiquitin (polyubiquitin chains) or a linear polymer linked via the initiator Met of the ubiquitin (linear polyubiquitin chains). Polyubiquitin chains, when attached to a target protein, have different functions depending on the Lys residue of the ubiquitin that is linked: Lys-6-linked may be involved in DNA repair; Lys-11-linked is involved in ERAD (endoplasmic reticulum-associated degradation) and in cell-cycle regulation; Lys-29-linked is involved in lysosomal degradation; Lys-33-linked is involved in kinase modification; Lys-48-linked is involved in protein degradation via the proteasome; Lys-63-linked is involved in endocytosis, DNA-damage responses as well as in signaling processes leading to activation of the transcription factor NF-kappa-B. Linear polymer chains formed via attachment by the initiator Met lead to cell signaling. Ubiquitin is usually conjugated to Lys residues of target proteins, however, in rare cases, conjugation to Cys or Ser residues has been observed. When polyubiquitin is free (unanchored-polyubiquitin), it also has distinct roles, such as in activation of protein kinases, and in signaling.[4] [5] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedInsulin-degrading enzyme (IDE) can degrade insulin and amyloid-beta, peptides involved in diabetes and Alzheimer's disease, respectively. IDE selects its substrates based on size, charge, and flexibility. From these criteria, we predict that IDE can cleave and inactivate ubiquitin (Ub). Here, we show that IDE cleaves Ub in a biphasic manner, first, by rapidly removing the two C-terminal glycines (k(cat)=2 s(-1)) followed by a slow cleavage between residues 72 and 73 (k(cat)=0.07 s(-1)), thereby producing the inactive 1-74 fragment of Ub (Ub1-74) and 1-72 fragment of Ub (Ub1-72). IDE is a ubiquitously expressed cytosolic protein, where monomeric Ub is also present. Thus, Ub degradation by IDE should be regulated. IDE is known to bind the cytoplasmic intermediate filament protein nestin with high affinity. We found that nestin potently inhibits the cleavage of Ub by IDE. In addition, Ub1-72 has a markedly increased affinity for IDE ( approximately 90-fold). Thus, the association of IDE with cellular regulators and product inhibition by Ub1-72 can prevent inadvertent proteolysis of cellular Ub by IDE. Ub is a highly stable protein. However, IDE instead prefers to degrade peptides with high intrinsic flexibility. Indeed, we demonstrate that IDE is exquisitely sensitive to Ub stability. Mutations that only mildly destabilize Ub (DeltaDeltaG<0.6 kcal/mol) render IDE hypersensitive to Ub with rate enhancements greater than 12-fold. The Ub-bound IDE structure and IDE mutants reveal that the interaction of the exosite with the N-terminus of Ub guides the unfolding of Ub, allowing its sequential cleavages. Together, our studies link the control of Ub clearance with IDE. Ubiquitin is a novel substrate for human insulin-degrading enzyme.,Ralat LA, Kalas V, Zheng Z, Goldman RD, Sosnick TR, Tang WJ J Mol Biol. 2011 Feb 25;406(3):454-66. Epub 2010 Dec 23. PMID:21185309[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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