Signal Peptide Peptidase
Signal peptide peptidase is an atypical aspartic protease that hydrolyzes peptide bonds within the transmembrane domain of substrates and is implicated in several biolgical and pathological functions.
Abstract from: the Journal of Biological Chemistry, 2011 Jul 22;286(29):26188-97. Epub 2011 Jun 2.
Miyashita H, Maruyama Y, Isshiki H, Osawa S, Ogura T, Mio K, Sato C, Tomita T, Iwatsubo T.
Department of Neuropathology and Neuroscience, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033.
Signal peptide peptidase (SPP) is an atypical aspartic protease that hydrolyzes peptide bonds within the transmembrane domain of substrates and is implicated in several biological and pathological functions. Here, we analyzed the structure of human SPP by electron microscopy and reconstructed the three-dimensional structure at a resolution of 22 Å. Enzymatically active SPP forms a slender, bullet-shaped homotetramer with dimensions of 85 × 85 × 130 Å. The SPP complex has four concaves on the rhombus-like sides, connected to a large chamber inside the molecule. Intriguingly, the N-terminal region of SPP is sufficient for the tetrameric assembly. Moreover, overexpression of the N-terminal region inhibited the formation of the endogenous SPP tetramer and the proteolytic activity within cells. These data suggest that the homotetramer is the functional unit of SPP and that its N-terminal region, which works as the structural scaffold, has a novel modulatory function for the intramembrane-cleaving activity of SPP.