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Int J Biol Macromol. 2017 Sep;102:29-41. doi: 10.1016/j.ijbiomac.2017.04.008. Epub 2017 Apr 4.

Expression in Escherichia coli of cysteine protease inhibitors from cowpea (Vigna unguiculata): The crystal structure of a single-domain cystatin gives insights on its thermal and pH stability.

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Departamento de Biologia, Centro de Ciências, Universidade Federal do Ceará (UFC), Fortaleza, CE, Brazil.
Laboratório de Biofísica Molecular, Departamento de Biologia Celular, Universidade de Brasília, Brasília, DF, Brazil.
Instituto de Física de São Carlos, Universidade de São Paulo, Brazil.
Departamento de Física, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Brazil.
Departamento de Bioquímica, Centro de Biociências, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil.
Departamento de Bioquímica e Biologia Molecular, Centro de Ciências, UFC, Fortaleza, CE, Brazil.
Departamento de Biologia, Centro de Ciências, Universidade Federal do Ceará (UFC), Fortaleza, CE, Brazil. Electronic address:


Two cysteine proteinase inhibitors from cowpea, VuCys1 and VuCys2, were produced in E. coli ArcticExpress (DE3). The recombinant products strongly inhibited papain and chymopapain as well as the midgut proteases from Callosobruchus maculatus larvae, a bruchid that uses cysteine proteases as major digestive enzymes. Heat treatment at 100°C for up to 60min or incubation at various pH values caused little reduction in the papain inhibitory activity of both inhibitors. Moreover, minor conformational variations, as probed by circular dichroism spectroscopy, were observed after VuCys1 and VuCys2 were subjected to these treatments. The crystal structure of VuCys1 was determined at a resolution of 1.95Å, revealing a domain-swapped dimer in the asymmetric unit. However, the two lobes of the domain-swapped dimer are positioned closer to each other in VuCys1 in comparison to other similar cystatin structures. Moreover, some polar residues from opposite lobes recruit water molecules, forming a hydrogen bond network that mediates contacts between the lobes, thus generating an extended open interface. Due to the closer distance between the lobes, a small hydrophobic core is also formed, further stabilizing the folded domain-swapped dimer. These structural features might account for the extraordinary thermal and pH stability of VuCys1.


Domain-swapped dimer; Phytocystatin; Recombinant

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