1p5c
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Circular permutation of Helix A in T4 lysozyme
OverviewOverview
In T4 lysozyme, helix A is located at the amino terminus of the sequence, but is associated with the C-terminal domain in the folded structure. To, investigate the implications of this arrangement for the folding of the, protein, we first created a circularly permuted variant with a new amino, terminus at residue 12. In effect, this moves the sequence corresponding, to helix A from the N- to the C-terminus of the molecule. The protein, crystallized nonisomorphously with the wild type but has a very similar, structure, showing that the unit consisting of helix A and the C-terminal, domain can be reconstituted from a contiguous polypeptide chain. The, protein is less stable than the wild type but folds slightly faster. We, then produced a second variant in which the helix A sequence was appended, at the C-terminus (as in the first variant), but was also restored at the, N-terminus (as in the wild type). This variant has two helix A sequences, one at the N-terminus and the other at the C-terminus, each of which can, compete for the same site in the folded protein. The crystal structure, shows that it is the N-terminal sequence that folds in a manner similar to, that of the wild type, whereas the copy at the C-terminus is forced to, loop out. The stability of this protein is much closer to that of the wild, type, but its rate of folding is significantly slower. The reduction in, rate is attributed to the presence of the two identical sequence segments, which compete for a single, mutually exclusive, site.
About this StructureAbout this Structure
1P5C is a Single protein structure of sequence from Bacteriophage t4. Active as Lysozyme, with EC number 3.2.1.17 Full crystallographic information is available from OCA.
ReferenceReference
Relocation or duplication of the helix A sequence of T4 lysozyme causes only modest changes in structure but can increase or decrease the rate of folding., Sagermann M, Baase WA, Mooers BH, Gay L, Matthews BW, Biochemistry. 2004 Feb 10;43(5):1296-301. PMID:14756565
Page seeded by OCA on Tue Nov 20 23:29:11 2007