Molecular and in vivo studies of a glutamate-class prolyl-endopeptidase for coeliac disease therapy.

The digestion of gluten generates toxic peptides, among which a highly immunogenic proline-rich 33-mer from wheat α-gliadin, that trigger coeliac disease. Neprosin from the pitcher plant is a reported prolyl endopeptidase. Here, we produce recombinant neprosin and its mutants, and find that full-length neprosin is a zymogen, which is self-activated at gastric pH by the release of an all-ß pro-domain via a pH-switch mechanism featuring a lysine plug. The catalytic domain is an atypical 7+8-stranded ß-sandwich with an extended active-site cleft containing an unprecedented pair of catalytic glutamates. Neprosin efficiently degrades both gliadin and the 33-mer in vitro under gastric conditions and is reversibly inactivated at pH > 5. Moreover, co-administration of gliadin and the neprosin zymogen at the ratio 500:1 reduces the abundance of the 33-mer in the small intestine of mice by up to 90%. Neprosin therefore founds a family of eukaryotic glutamate endopeptidases that fulfils requisites for a therapeutic glutenase.

An Integrative Structural Biology Analysis of Von Willebrand Factor Binding and Processing by ADAMTS-13 in Solution.

Von Willebrand Factor (vWF), a 300-kDa plasma protein key to homeostasis, is cleaved at a single site by multi-domain metallopeptidase ADAMTS-13. vWF is the only known substrate of this peptidase, which circulates in a latent form and becomes allosterically activated by substrate binding. Herein, we characterised the complex formed by a competent peptidase construct (AD13-MDTCS) comprising metallopeptidase (M), disintegrin-like (D), thrombospondin (T), cysteine-rich (C), and spacer (S) domains, with a 73-residue functionally relevant vWF-peptide, using nine complementary techniques. Pull-down assays, gel electrophoresis, and surface plasmon resonance revealed tight binding with sub-micromolar affinity. Cross-linking mass spectrometry with four reagents showed that, within the peptidase, domain D approaches M, C, and S. S is positioned close to M and C, and the peptide contacts all domains. Hydrogen/deuterium exchange mass spectrometry revealed strong and weak protection for C/D and M/S, respectively. Structural analysis by multi-angle laser light scattering and small-angle X-ray scattering in solution revealed that the enzyme adopted highly flexible unbound, latent structures and peptide-bound, active structures that differed from the AD13-MDTCS crystal structure. Moreover, the peptide behaved like a self-avoiding random chain. We integrated the results with computational approaches, derived an ensemble of structures that collectively satisfied all experimental restraints, and discussed the functional implications. The interaction conforms to a 'fuzzy complex' that follows a 'dynamic zipper' mechanism involving numerous reversible, weak but additive interactions that result in strong binding and cleavage. Our findings contribute to illuminating the biochemistry of the vWF:ADAMTS-13 axis.

Recombinant production of human α2-macroglobulin variants and interaction studies with recombinant G-related α2-macroglobulin binding protein and latent transforming growth factor-ß2.

α2-Macroglobulins (α2Ms) regulate peptidases, hormones and cytokines. Mediated by peptidase cleavage, they transit between native, intact forms and activated, induced forms. α2Ms have been studied over decades using authentic material from primary sources, which was limited by sample heterogeneity and contaminants. Here, we developed high-yield expression systems based on transient transfection in Drosophila Schneider 2 and human Expi293F cells, which produced pure human α2M (hα2M) at ~1.0 and ~0.4 mg per liter of cell culture, respectively. In both cases, hα2M was mainly found in the induced form. Shorter hα2M variants encompassing N-/C-terminal parts were also expressed and yielded pure material at ~1.6/~1.3 and ~3.2/~4.6 mg per liter of insect or mammalian cell culture, respectively. We then analyzed the binding of recombinant and authentic hα2M to recombinant latent human transforming growth factor-ß2 (pro-TGF-ß2) and bacterial G-related α2M binding protein (GRAB) by surface plasmon resonance, multiple-angle laser light scattering, size-exclusion chromatography, fluorogenic labelling, gel electrophoresis and Western-blot analysis. Two GRAB molecules formed stable complexes of high affinity with native and induced authentic hα2M tetramers. The shorter recombinant hα2M variants interacted after preincubation only. In contrast, pro-TGF-ß2 did not interact, probably owing to hindrance by the N-terminal latency-associated protein of the cytokine.

Recombinant production, purification, crystallization, and structure analysis of human transforming growth factor ß2 in a new conformation.

Transforming growth factor ß is a disulfide-linked dimeric cytokine that occurs in three highly related isoforms (TGFß1-TGFß3) engaged in signaling functions through binding of cognate TGFß receptors. To regulate this pathway, the cytokines are biosynthesized as inactive pro-TGFßs with an N-terminal latency-associated protein preceding the mature moieties. Due to their pleiotropic implications in physiology and pathology, TGFßs are privileged objects of in vitro studies. However, such studies have long been limited by the lack of efficient human recombinant expression systems of native, glycosylated, and homogenous proteins. Here, we developed pro-TGFß2 production systems based on human Expi293F cells, which yielded >2 mg of pure histidine- or Strep-tagged protein per liter of cell culture. We assayed this material biophysically and in crystallization assays and obtained a different crystal form of mature TGFß2, which adopted a conformation deviating from previous structures, with a distinct dimeric conformation that would require significant rearrangement for binding of TGFß receptors. This new conformation may be reversibly adopted by a certain fraction of the mature TGß2 population and represent a hitherto undescribed additional level of activity regulation of the mature growth factor once the latency-associated protein has been separated.