Hydrated and Dehydrated Tertiary Interactions - Opening and Closing - of a Four-helix Bundle Peptide

• The structural heterogeneity and thermal denaturation of a dansyl-labeled four-helix bundle homodimeric peptide has been studied with steady state and time-resolved fluorescence spectroscopy and with circular dichroism. At room temperature the fluorescence decay of the polarity-sensitive dansyl, located in the hydrophobic core region, can be described by a broad distribution of fluorescence lifetimes, reflecting the heterogeneous microenvironment. However, the lifetime distribution is nearly bimodal, which we ascribe to the presence of two major conformational subgroups. Since the fluorescence lifetime reflects the water content of the four-helix bundle conformations we can use the lifetime analysis to monitor the change of hydration state of the hydrophobic core of the four-helix bundle. Increasing the temperature from 9 °C to 23 °C leads to an increased population of molten-globule-like conformations with a less ordered helical backbone structure. The fluorescence emission maximum remains constant in this temperature interval, and the hydrophobic core is not strongly affected. Above 30 °C the structural dynamics involve transient openings of the four-helix bundle structure as evidenced by the emergence of a water-quenched component and less negative CD. Above 60 °C the homodimer starts to dissociate, as shown by the increasing loss of CD and narrow, short-lived fluorescence lifetime distributions.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Medicinska och farmaceutiska grundvetenskaper -- Andra medicinska och farmaceutiska grundvetenskaper (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Basic Medicine -- Other Basic Medicine (hsv//eng)

Nyckelord

time-resolved fluorescence spectroscopy

protein dynamics

CD-spectroscopy

Chemistry

Kemi

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