The disulphide bonds in the catalytic domain of BACE are critical but not essential for amyloid precursor protein processing activity

Abstract

b-Site APP-cleaving enzyme (BACE) initiates the processing of the amyloid precursor protein (APP) leading to the generation of b-amyloid, the main component of Alzheimer's disease senile plaques. BACE (Asp2, memapsin 2) is a type I transmembrane aspartic protease responsible for the b-secretase cleavage of APP producing a soluble form of the ectodomain (sAPPb) and the membrane-bound, carboxy-terminal intermediates C99 and C89. BACE maturation involves cysteine bridge formation, N-glycosylation and propeptide removal. We investigated variants of BACE in which the disulphide bonds of the catalytic domain spanning between Cys216/Cys420, Cys278/Cys443 and Cys330/Cys380 were removed by mutagenesis. When transfected in cultured cells, these mutants showed impaired maturation. Nevertheless, a fraction of mutated protein retained both the competence to mature as well as the activity to process APP. For the generation of a functional enzyme the conserved Cys330/Cys380 bond was the most critical, whereas the two bonds between Cys216/Cys420 and Cys278/Cys443, which are typical for the membrane-bound BACE, appeared to be less important.

The Folding Process of Acylphosphatase from Escherichia coli is Remarkably Accelerated by the Presence of a Disulfide Bond

“…Similar properties have previously been shown also in partially folded states of other proteins. 13,52 Our results suggest that the removal of the disulfide bond causes a large reduction, by over 3 orders of magnitude, of the folding rate and has, by contrast, only a small influence on the unfolding rate. Indeed, the unfolding rate extrapolated to the absence of denaturant is comparable in the two protein variants with and without the disulfide bond ( Table 2).…”

Proteases and Proteolysis in Alzheimer Disease: A Multifactorial View on the Disease Process

“…2). BACE1 is A-glycosylated, sulfated, phosphorylated, and palmitoylated (21,39,49,80,131,330), and the propeptide of BACE1 is removed by a member of the furin family (21,49), generating a mature protease. A fraction of BACE1 is also shed from the cell surface after cleavage by a metalloprotease, probably ADAM 10 (132), but the significance of shed BACE1 is unknown.…”

Understanding BACE1: essential protease for amyloid-β production in Alzheimer’s disease

“…The BACE proteins represent a novel subgroup of this family, being the first reported aspartic proteases to contain a transmembrane domain and carboxyl terminal extension [12], and also possessing unique disulphide bridge distribution (Fig. 2) [33,34]. The eight known functional human A1 aspartic proteases vary in genomic structure, with BACE2 being the largest and napsin the smallest.…”

“…2). BACE1 disulphide bridges maintain correct folding and orientation of BACE, but are not vital to its enzymatic activity [33,34]. In addition, the unique transmembrane regions of BACE1 and BACE2 confer an evolutionary specialisation, allowing their sequestration to membranes of specific organelles and the plasma membrane.…”