Search

Acetoacetyl-CoA synthetase (AACS) is a ketone body-utilizing enzyme and is responsible for the synthesis of cholesterol and fatty acids. We have previously shown that AACS is cleaved by legumain, a lysosomal asparaginyl endopeptidase. In this study, we attempted to determine the cleavage site of AACS. Mutagenesis analysis of AACS revealed that Asn547 is the specific cleavage site of AACS in mouse livers. The cleaved form of AACS (1-547) lost the ability to convert acetoacetate to acetoacetyl-CoA. Moreover, hydrodynamics-based gene transduction showed that overexpression of AACS (1-547) increases the protein expression of caveolin-1, the principal component of the caveolae. These results suggest that cleavage of AACS by legumain is critical for the regulation of enzymatic activity and results in gain-of-function changes.

Legumain/asparaginyl endopeptidase (EC 3.4.22.34) is a novel cysteine protease that is abundantly expressed in the late endosomes and lysosomes of renal proximal tubular cells. Recently, emerging evidence has indicated that legumain might play an important role in control of extracellular matrix turnover in various pathological conditions such as tumor growth/metastasis and progression of atherosclerosis. We initially found that purified legumain can directly degrade fibronectin, one of the main components of the extracellular matrix, in vitro. Therefore, we examined the effect of legumain on fibronectin degradation in cultured mouse renal proximal tubular cells. Fibronectin processing can be inhibited by chloroquine, an inhibitor of lysosomal degradation, and can be enhanced by the overexpression of legumain, indicating that fibronectin degradation occurs in the presence of legumain in lysosomes from renal proximal tubular cells. Furthermore, in legumain-deficient mice, unilateral ureteral obstruction (UUO)-induced renal interstitial protein accumulation of fibronectin and renal interstitial fibrosis were markedly enhanced. These findings indicate that legumain might have an important role in extracellular matrix remodeling via the degradation of fibronectin in renal proximal tubular cells.

Asparaginyl endopeptidases, or legumains, are a recently identified family of cysteine-class endopeptidases. A single gene encoding a Schistosoma mansoni asparaginyl endopeptidase (a.k.a. Sm32 or schistosome legumain) has been reported, but by sequence homology it would be expected to yield an inactive product as the active site C197 had been replaced by N. We now describe a new S. mansoni gene in which C197 is present. Both gene products were expressed in Pichia pastoris. Autocatalytic processing to fully active C197 Sm32 occurred at acid pH. In contrast, N197 Sm32 was not processed and this is consistent with the hypothesis that C197 is essential for catalysis. This was confirmed by mutation of N197 to C and re-expression in Pichia. The availability of recombinant active Sm32 allows detailed analysis of its catalytic mechanism and its function(s) in the biology of this important human parasite.

Human legumain was characterized following overexpression in a murine cell line as the C-terminal Ig-fusion protein. Upon acid treatment, the prolegumain autoproteolyzed distal to two aspartic acid residues to yield a highly active form. The ability of mature legumain to cleave after aspartic acid residues was confirmed with a small peptide substrate. Substitution of alanine for the putative catalytic cysteine, or for either of two strictly conserved histidine residues, partly or wholly eliminated autoactivation but not the ability of wild-type legumain to correctly process the variants to the properly sized proteins.

Plant legumains are cysteine proteinases putatively involved in processing endogenous proteins. Phytocystatins (PhyCys) have been described as plant inhibitors of papain-like cysteine proteinases. Some PhyCys contain a carboxy terminal extension with an amino acid motif (SNSL) similar to that involved in the inhibition of legumain-like proteins by human cystatins. The role of these carboxy terminal extended PhyCys as inhibitors of legumain-like cysteine proteinases is here shown by in vitro inhibition of human legumain and legumain-like activities from barley extracts. Moreover, site-directed mutagenesis has demonstrated that the asparagine of the SNSL motif is essential in this inhibition. We prove for first time the existence of legumain inhibitors in plants.

We show by site-directed mutagenesis that the catalytic residues of mammalian legumain, a recently discovered lysosomal asparaginycysteine endopeptidase, form a catalytic dyad in the motif His-Gly-spacer-Ala-Cys. We note that the same motif is present in the caspases, aspartate-specific endopeptidases central to the process of apoptosis in animal cells, and also in the families of clostripain and gingipain which are arginyl/lysyl endopeptidases of pathogenic bacteria. We propose that the four families have similar protein folds, are evolutionarily related in clan CD, and have common characteristics including substrate specificities dominated by the interactions of the S1 subsite.

Asparaginyl endopeptidases, or legumains, are a recently identified family of cysteine-class endopeptidases. A single gene encoding a Schistosoma mansoni asparaginyl endopeptidase (a.k.a. Sm32 or schistosome legumain) has been reported, but by sequence homology it would be expected to yield an inactive product as the active site C197 had been replaced by N. We now describe a new S. mansoni gene in which C197 is present. Both gene products were expressed in Pichia pastoris. Autocatalytic processing to fully active C197 Sm32 occurred at acid pH. In contrast, N197 Sm32 was not processed and this is consistent with the hypothesis that C197 is essential for catalysis. This was confirmed by mutation of N197 to C and re-expression in Pichia. The availability of recombinant active Sm32 allows detailed analysis of its catalytic mechanism and its function(s) in the biology of this important human parasite.

Corrigendum to ‘‘Legumain/asparaginyl endopeptidase controls extracellular matrix remodeling through the degradation of fibronectin in mouse renal proximal tubular cells’’ [FEBS Lett. 581 (2007) 1417–1424] Yoshikata Morita, Hisazumi Araki, Toshiro Sugimoto*, Keisuke Takeuchi, Takuya Yamane, Toshinaga Maeda, Yoshio Yamamoto, Katsuji Nishi, Masahide Asano, Kanae Shirahama-Noda, Mikio Nishimura, Takashi Uzu, Ikuko Hara-Nishimura, Daisuke Koya, Atsunori Kashiwagi, Iwao Ohkubo a Department of Medical Biochemistry, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan b Department of Internal Medicine, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan c Legal Medicine, Shiga University of Medical Science, Seta, Otsu 520-2192, Japan d Division of Endocrinology and Metabolism, Kanazawa Medical University, Ishikawa 920-0293, Japan e Advanced Science Research Center, Kanazawa University, Takaramachi, Kanazawa 920-8640, Japan f Department of Cell Biology, National Institute for Basic Biology, Okazaki 444-8585, Japan g Graduate School of Science, Kyoto University, Kitashirakawa, Sakyo-ku, Kyoto 606-8502, Japan