Zusammenfassung
Peruvianin-I is a cysteine peptidase (EC 3.4.22) purified from Thevetia
peruviana. Previous studies have shown that it is the only germin-like
protein (GLP) with proteolytic activity described so far. In this work,
the X-ray crystal structure of peruvianin-I was determined to a
resolution of 2.15 angstrom (PDB accession number: 6ORM) and its
specific location was evaluated by different assays. Its overall
structure shows an arrangement composed of a homohexamer (a trimer of
dimers) where each monomer exhibits a typical beta-barrel fold and two
glycosylation sites (Asn(55) and Asn(1)(44)). Analysis of its active
site confirmed the absence of essential amino acids for typical oxalate
oxidase activity of GLP5. Details of the active site and molecular
docking results, using a specific cysteine peptidase inhibitor
(iodoacetamide), were used to discuss a plausible mechanism for
proteolytic activity of peruvianin-I. Histological analyses showed that
T. peruviana has articulated anastomosing laticifers, i.e., rows of
cells which merge to form continuous tubes throughout its green organs.
Moreover, peruvianin-I was detected exclusively in the latex. Because
latex peptidases have been described as defensive molecules against
insects, we hypothesize that peruvianin-I contributes to protect T.
peruviana plants against herbivory.
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