A gamma-secretase-like intramembrane cleavage of TNFalpha by the GxGD aspartyl protease SPPL2b.
ABSTRACT Gamma-secretase and signal peptide peptidase (SPP) are unusual GxGD aspartyl proteases, which mediate intramembrane proteolysis. In addition to SPP, a family of SPP-like proteins (SPPLs) of unknown function has been identified. We demonstrate that SPPL2b utilizes multiple intramembrane cleavages to liberate the intracellular domain of tumor necrosis factor alpha (TNFalpha) into the cytosol and the carboxy-terminal counterpart into the extracellular space. These findings suggest common principles for regulated intramembrane proteolysis by GxGD aspartyl proteases.
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ABSTRACT: Rhomboid proteases reside within cellular membranes, but the advantage of this unusual environment is unclear. We discovered membrane immersion allows substrates to be identified in a fundamentally-different way, based initially upon exposing 'masked' conformational dynamics of transmembrane segments rather than sequence-specific binding. EPR and CD spectroscopy revealed that the membrane restrains rhomboid gate and substrate conformation to limit proteolysis. True substrates evolved intrinsically-unstable transmembrane helices that both become unstructured when not supported by the membrane, and facilitate partitioning into the hydrophilic, active-site environment. Accordingly, manipulating substrate and gate dynamics in living cells shifted cleavage sites in a manner incompatible with extended sequence binding, but correlated with a membrane-and-helix-exit propensity scale. Moreover, cleavage of diverse non-substrates was provoked by single-residue changes that destabilize transmembrane helices. Membrane immersion thus bestows rhomboid proteases with the ability to identify substrates primarily based on reading their intrinsic transmembrane dynamics.DOI:http://dx.doi.org/10.7554/eLife.00173.001.eLife Sciences 11/2012; 1:e00173. DOI:10.7554/eLife.00173 · 8.52 Impact Factor
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ABSTRACT: Accumulations of insoluble deposits of amyloid β-peptide are major pathological hallmarks of Alzheimer disease. Amyloid β-peptide is derived by sequential proteolytic processing from a large type I trans-membrane protein, the β-amyloid precursor protein. The proteolytic enzymes involved in its processing are named secretases. β- and γ-secretase liberate by sequential cleavage the neurotoxic amyloid β-peptide, whereas α-secretase prevents its generation by cleaving within the middle of the amyloid domain. In this chapter we describe the cell biological and biochemical characteristics of the three secretase activities involved in the proteolytic processing of the precursor protein. In addition we outline how the precursor protein maturates and traffics through the secretory pathway to reach the subcellular locations where the individual secretases are preferentially active. Furthermore, we illuminate how neuronal activity and mutations which cause familial Alzheimer disease affect amyloid β-peptide generation and therefore disease onset and progression.Cold Spring Harbor Perspectives in Medicine 05/2012; 2(5):a006270. DOI:10.1101/cshperspect.a006270 · 7.56 Impact Factor
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ABSTRACT: Presenilin is the catalytic component of gamma-secretase, a complex aspartyl protease and a founding member of intramembrane-cleaving proteases. gamma-Secretase is involved in the pathogenesis of Alzheimer's disease and a top target for therapeutic intervention. However, the protease complex processes a variety of transmembrane substrates, including the Notch receptor, raising concerns about toxicity. Nevertheless, gamma-secretase inhibitors and modulators have been identified that allow Notch processing and signaling to continue, and promising compounds are entering clinical trials. Molecular and biochemical studies offer a model for how this protease hydrolyzes transmembrane domains in the confines of the lipid bilayer. Progress has also been made toward structure elucidation of presenilin and the gamma-secretase complex by electron microscopy as well as by studying cysteine-mutant presenilins. The signal peptide peptidase (SPP) family of proteases are distantly related to presenilins. However, the SPPs work as single polypeptides without the need for cofactors and otherwise appear to be simple model systems for presenilin in the gamma-secretase complex. SPP biology, structure, and inhibition will also be discussed.Biological Chemistry 08/2010; 391(8):839-47. DOI:10.1515/BC.2010.086 · 2.69 Impact Factor