Crystal structure of human thimet oligopeptidase provides insight into substrate recognition, regulation, and localization.
Thimet oligopeptidase (TOP) is a zinc metallopeptidase that metabolizes a number of bioactive peptides and degrades peptides released by the proteasome, limiting antigenic presentation by MHC class I molecules. We present the crystal structure of human TOP at 2.0-A resolution. The active site is located at the base of a deep channel that runs the length of the elongated molecule, an overall fold first seen in the closely related metallopeptidase neurolysin. Comparison of the two related structures indicates hinge-like flexibility and identifies elements near one end of the channel that adopt different conformations. Relatively few of the sequence differences between TOP and neurolysin map to the proposed substrate-binding site, and four of these variable residues may account for differences in substrate specificity. In addition, a loop segment (residues 599-611) in TOP differs in conformation and degree of order from the corresponding neurolysin loop, suggesting it may also play a role in activity differences. Cysteines thought to mediate covalent oligomerization of rat TOP, which can inactivate the enzyme, are found to be surface-accessible in the human enzyme, and additional cysteines (residues 321,350, and 644) may also mediate multimerization in the human homolog. Disorder in the N terminus of TOP indicates it may be involved in subcellular localization, but a potential nuclear import element is found to be part of a helix and, therefore, unlikely to be involved in transport. A large acidic patch on the surface could potentially mediate a protein-protein interaction, possibly through formation of a covalent linkage.
Ray
Kallol
K
Department of Molecular and Cellular Biochemistry and Center for Structural Biology, University of Kentucky, Lexington, KY 40536, USA.
Hines
Christina S
CS
Coll-Rodriguez
Jerry
J
Rodgers
David W
DW
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006801:Humans; D008666:Metalloendopeptidases / Q000737:chemistry*; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D051381:Rats; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
D008666:Metalloendopeptidases; C022510:thimet oligopeptidase; C062316:neurolysin