Crystal structure of cytoplasmic Escherichia coli peptidyl-prolyl isomerase: Evidence for decreased mobility of loops upon complexation

The structure of the unliganded form of the Escherichia coli cytoplasmic peptidyl-prolyl isomerase (ppiB gene product) in a new crystal form was determined by the molecular replacement method and refined to an R-factor of 16.1% at 2.1 Å resolution. The enzyme crystallized in the orthorhombic C2221 space group with unit cell dimensions of n = 44.7 Å, b = 68.2 Å and c = 102.0 Å. Comparison with the reported structure of the enzyme complexed with the tripeptide substrate succinyl-Ala-Pro-Ala-p-nitroanilide revealed subtle changes that occur upon complex formation. There is evidence to suggest that two surface loops have significantly reduced mobility in the complexed structure.