 |
|
Title
|
|
Structural effects induced by removal of a disulfide-bridge: the X-ray structure of the C30A/C51A mutant of basic pancreatic trypsin inhibitor at 1.6 A.
|
|
|
Authors
|
|
C.Eigenbrot,
M.Randal,
A.A.Kossiakoff.
|
|
|
Ref.
|
|
Protein Eng, 1990,
3,
591-598.
|
|
|
PubMed id
|
|
|
|
|
|
Abstract
|
|
|
The X-ray structure of a variant of basic pancreatic trypsin inhibitor (BPTI)
has been analyzed to determine the structural accommodation resulting from
removal of a disulfide cross-link in a protein. The disulfide removed,
Cys30-Cys51, has been implicated in both the folding pathway of the protein and
its overall thermal stability. In the variant studied, C30A/C51A, the disulfide
cysteines were replaced by less bulky alanines. The atomic displacements
observed for C30A/C51A indicate a set of concerted shifts of two segments of
chains, which together significantly diminish a packing defect at the site of
the removed cysteine sulfur atoms. The observed structural changes are
distributed asymmetrically around the sites of mutation, indicating that the
adjacent beta-sheet is more resistant to the perturbation than the alpha-helix
on the opposite side of the disulfide bond. The thermal parameters of groups
involved in the structural accommodation are not significantly altered. A
comparison of the X-ray structures reported for native BPTI determined in three
different crystal forms indicates that the magnitude of its conformational
variability exceeds that of the structural changes caused by the disulfide
removal. This emphasizes the necessity of using isomorphous crystal systems to
determine the relatively small effects due to mutation.
|
|
|
|