D. Pignol et al., CRYSTALLOGRAPHIC STUDY OF A CLEAVED, NON-ACTIVATABLE FORM OF PORCINE ZYMOGEN-E, Journal of Molecular Biology, 252(1), 1995, pp. 20-24
The crystal structure of a cleaved form of porcine zymogen E has been
solved by molecular replacement using the bovine procarboxypeptidase A
-S6 subunit III structure as search model. Crystallographic refinement
using simulated annealing and energy minimization techniques resulted
in a final R-factor of 0.189 for all data between 8 and 2.3 Angstrom
resolution. The zymogen E three-dimensional model is very close to tha
t of bovine subunit III and represents the second member of the zymoge
n E family for which the crystal structure is known. The two structure
s indicate that, in contrast to trypsinogen and chymotrypsinogen, zymo
gens of this family are highly organized molecules. The amino acid seq
uence of zymogen. E has only been determined for the first 40 residues
. Based on the electron density map, we have introduced six sequence c
hanges relative to subunit III. Out of the 11 residues in the activati
on peptide, only the first six present well matching electron density;
they are connected to the rest of the zymogen by an unexpected Cys1-C
ys122 disulphide bridge (according to the bovine chymotrypsinogen A nu
mbering system). Amino acid sequencing of protein solutions both from
dissolved crystals and from the initial stock clearly indicated that t
he Val17-Asn18 bond had been cleaved during the crystallization proces
s. This result adds weight to the assumption that the autolysis of the
bovine zymogen E gives rise to subunit III and that this maybe a regu
latory mechanism for protease E activity. (C) 1995 Academic Press Limi
ted