Proceedings book download - 5Z.com

stabilization are the non-H-bonded sites closest to the turn and closest to the chain termini.In the case of the turn-flanking W/W interaction, the fold stabilization is most dramatic for[4:6]- and [2:4]-hairpins with a type I’ turn.The stabilization that results when the W/Wpair, together with essential flankinginteractions, is present at the non-H-bondedsite at the hairpin termini is discussed in anaccompanying report.The [4:6]-hairpin series providesexamples of the extent to which a turnflankingW/W can provide stabilization andalso some of the more interesting hairpindynamics results that have come from “edge-H 3” exchange broadening data. Theoptimized NPATGK turn sequence [5] can replace a variety of 5- and 4-residue sequencesin other hairpins without loss of fold stability. However, the NAAAXX sequences shown inTable 1 require the turn-flanking W/W in order to display significant hairpin formation. Forexample, while KTW-NAAAKK-WTE is nearly as stable as the corresponding NPATGKcompound, KKLWVS-NAAAKK-KIWVSA (with the W/W unit moved to a central ratherthan the turn-flanking non-H-bonded site) does not display a detectable hairpin foldpopulation even though KKLWVS-INGK-KIWVSA has a stable hairpin fold.In previous studies of hairpin folding dynamics with identical strands, the foldstabilizing effects of turn mutations are reflected in increases in k F . The data in Table 1indicates that loop sequence can have dramatic effects on folding rates even for systemswith identical fold stabilities. The line width data that affords these rates appear in Figure 3.In contrast the folding retardation seen in going from entry #1 to entry #4 (a C-terminal Eto A-NH 2 mutation) reflects the deletion of an attractive Coulombic interaction between theextreme termini of the hairpin strands. The acidification induced folding rate retardation(entries #5/6) provides additional evidence that this Coulombic interaction effects anincrease in folding rates. The dynamics data in Table 1 is viewed as inconsistent [6] with a“turn-formation first then zipper-up” mechanism for hairpin formation. We anticipate thathairpin constructs with W/W pairs will continue to be valuable systems for elucidationfolding mechanisms and requisites.AcknowledgmentsSupported by grants CHE-0650318 (NSF) and GM59658 (NIH).Fig. 3. Lineshapes of the two H 3.signalsfor entries #1 and #3.Table 1. Folding dynamics of KTW-NXXXXX-WTX peptides ([4:6]-hairpins) at 300KPeptide sequence (H 3) ex (Hz) 1/k F ( s) 1/k U ( s) Entry#KTW-NPATGK-WTE a 5.49 a 1.67 0.34 1.89 1KTW-NAAAGK-WTE 5.28 5.89 2.15 27.26 2KTW-NAAAKK-WTE 5.34 34.27 9.83 89.61 3KTW-NPATGK-WTA-NH 2 5.99 12.79 2.00 3.47 4KTW-NAAAKT-WTE a 5.49 a 42.42 8.72 47.25 5at pH 3 6.13 101.20 16.37 23.00 6a The identical H 3 shifts indicate equivalent fold stability even though the folding ratesdiffer by a factor of 25References1. Grishina, I., Woody, R. Faraday Discuss. 99, 245 (1994).2. Eidenschink, L., Kier, B., Huggins, K., Andersen, N. Proteins Struct. Funct. Bioinf. 75, 308 (2009).3. Kier, B., Shu, I., Eidenschink, L., Andersen, N. Proc. Natl. Acad. Sci. U.S.A. 107, 10466 (2010).4. Bunagan, M., Yang, X., Saven, J., Gai, F. J. Phys. Chem. B 110, 3759 (2006).5. Andersen, N., Olsen, K., Fesinmeyer, R., et al. J. Am. Chem. Soc. 128, 6101 (2006).6. Olsen, K., Andersen, N., et al. Proc. Natl. Acad. Sci. U.S.A. 102, 15483(2005) and refs cited therein.615