Proteins need fold to perform their biological function. Thus, understanding how
proteins fold could be the key to understanding life. In the first study, the stability and
structure of several !-hairpin peptide variants derived from the C-terminus of the B1
domain of protein G (PGB1) were investigated by a number of experimental and
computational techniques. Our analysis shows that the structure and stability of this
hairpin can be greatly affected by one or a few simple mutations. For example,
removing an unfavorable charge near the N-terminus of the peptide (Glu42 to Gln or
Thr) or optimization of the N-terminal charge-charge interactions (Gly41 to Lys) both
stabilize the peptide, even in water. Furthermore, a simple replacement of a charged
residue in the turn (Asp47 to Ala) changes the !-turn conformation. Our results indicate
that the structure and stability of this !?hairpin peptide can be modulated in numerous
ways and thus contributes towards a more complete understanding of this important
model !-hairpin as well as to the folding and stability of larger peptides and proteins.
The second study revealed that PGB1 and its variants can form amyloid fibrils in
vitro under certain conditions and these fibrils resemble those from other proteins that have been implicated in diseases. To gain a further understanding of molecular
mechanism of PGB1 amyloid formation, we designed a set of variants with mutations
that change the local secondary structure propensity in PGB1, but have similar global
conformational stability. The kinetics of amyloid formation of all these variants have
been studied and compared. Our results show that different locations of even a single
mutation can have a dramatic effect on PGB1 amyloid formation, which is in sharp
contrast with a previous report. Our results also suggest that the "-helix in PGB1 plays
an important role in the amyloid formation process of PGB1.
In the final study, we investigate the forces that contribute to protein stability in a
very general manner. Based on what we have learned about the major forces that
contribute to the stability of globular proteins, protein stability should increase as the
size of the protein increases. This is not observed: the conformational stability of
globular proteins is independent of protein size. In an effort to understand why large
proteins are not more stable than small proteins, twenty single-domain globular proteins
ranging in size from 35 to 470 residues have been analyzed. Our study shows that nature
buries more charged groups and more non-hydrogen-bonded polar groups to destabilize
large proteins.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2009-05-304 |
| Date | 2009 May 1900 |
| Creators | Wei, Yun |
| Contributors | Scholtz, J. Martin |
| Source Sets | Texas A and M University |
| Language | English |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | application/pdf |
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